CodeMyVibe / Lab / Health map

Where the world gets sick less.

Some illnesses are far rarer in some places than others. Pick one to see where, the everyday habit researchers link to it, and how strong the evidence really is. Some popular ideas hold up. Some don't.

    World map
    Lower here Higher here Studied here (people compared within the country) Not part of this finding

    How we graded the evidence

    A country-to-country gap is a clue, not proof. Places that differ in one habit usually differ in money, age, genes, diet and how well they count disease. So every finding carries a grade and names the most likely other explanation.

    Strong
    Trials, or large long-term studies of individuals plus a known mechanism.
    Moderate
    Consistent studies of individuals, but real confounders remain.
    Weak
    Mostly country-vs-country comparisons, small or mixed studies.
    Myth
    A popular claim the evidence does not support.

    All 107 findings

    Every number is quoted from the source linked beside it. Checked October 2026.

    ConditionLinked habitEvidenceLower inHigher inStudied inKey numberSources
    Colorectal cancerUsing squat toilets instead of sitting toiletsMyth–––Iranian case-control study (2012; 100 colorectal cancer patients, 100 controls from hospital coronary care units): adjusted odds ratio for ever using a sitting toilet 1.07 (95% CI 0.72-1.59); per extra 10 years of sitting-toilet use, adjusted OR 1.02 (95% CI 0.74-1.40). Neither was statistically significant. A 2025 scoping review of 42 studies said small samples and poor control of confounders 'preclude definitive conclusions'.1. Middle East Journal of Digestive Diseases (4(1):23-27)
    2. BMC Public Health
    Colorectal cancerTraditional high-fiber, low-fat African diet (Burkitt's observation)ModerateSouth Africa, UgandaUnited States–O'Keefe et al., 2015: 'Rates of colon cancer are much higher in African Americans (65:100,000) than in rural South Africans (<5:100,000).' In 2-week supervised food swaps, African Americans eating a high-fibre, low-fat African-style diet and rural Africans eating a high-fat, low-fibre western-style diet showed 'remarkable reciprocal changes' in mucosal biomarkers of cancer risk. GLOBOCAN 2022 (via a 2024 analysis): Africa's colorectal cancer incidence rate 8.2 per 100,000 vs Oceania 31.1, Europe 30.5, North America 27.2.1. Nature Communications
    2. ecancermedicalscience
    3. Nutrition Research Reviews
    Colorectal cancerEating more dietary fiber and whole grainsModerate–––Reynolds et al., Lancet 2019 (185 prospective studies, just under 135 million person-years): 'Observational data suggest a 15-30% decrease in ... colorectal cancer when comparing the highest dietary fibre consumers with the lowest'. Aune et al., BMJ 2011 (25 prospective studies, 16 of them on total fibre): about 10% lower colorectal cancer risk for each extra 10 g of fibre a day (summary relative risk 0.90, 95% CI 0.86-0.94). Cochrane 2017 review of trials in people with past polyps (5 trials with usable data, 4,798 people): 'lack of evidence' that more fibre over 2 to 8 years reduces polyp recurrence or bowel cancer (low-quality evidence).1. The Lancet
    2. BMJ
    3. Cochrane Database of Systematic Reviews
    Colorectal cancerEating processed meat (ham, sausage, bacon, hot dogs) and red meatStrong–––IARC, 26 Oct 2015 (22 experts from 10 countries, more than 800 studies): processed meat classified Group 1, carcinogenic to humans; red meat Group 2A, probably carcinogenic. 'Each 50 gram portion of processed meat eaten daily increases the risk of colorectal cancer by 18%.' IARC's Dr Kurt Straif: 'For an individual, the risk ... remains small'.1. IARC / WHO
    Early-onset colorectal cancer (ages 25-49)Modern 'Western' lifestyle (diet, inactivity, excess weight) - suspected, not provenWeakUganda, IndiaAustralia, New Zealand, Puerto Rico, United States, South Korea–Sung et al., Lancet Oncology (published online 11 Dec 2024; data through 2017, 50 countries and territories): early-onset colorectal cancer (ages 25-49) rose in 27 of 50 and was stable in 23 over the latest 10 years. Fastest rises: New Zealand and Chile about 4.0% per year, Puerto Rico 3.8%, England 3.6%. Highest rates in the most recent five years: Australia, Puerto Rico, New Zealand, the U.S. and South Korea at about 14 to 17 per 100,000; lowest: Uganda (4.4) and India (3.5) per 100,000. U.S. (American Cancer Society, 2026): incidence rose 3% a year in ages 20-49 during 2013-2022.1. American Cancer Society / The Lancet Oncology
    2. The Lancet Oncology
    3. CA: A Cancer Journal for Clinicians
    Diverticular diseaseHigh-fiber dietModerateUgandaUnited Kingdom–Meta-analysis of 5 prospective cohorts (19,282 cases, 865,829 participants; Eur J Nutr 2020): about 26% lower risk of diverticular disease for each extra 10 g of fibre a day (summary relative risk 0.74, 95% CI 0.71-0.78), and 41% lower risk at 30 g/day than at 7.5 g/day. But Peery et al., Gastroenterology 2012 (2,104 colonoscopy patients aged 30-80): 'those with the lowest fiber intake were 30 percent less likely to develop diverticula' than those eating the most.1. European Journal of Nutrition
    2. Gastroenterology (DOI 10.1053/j.gastro.2011.10.035) via ScienceDaily
    3. The Lancet Gastroenterology & Hepatology
    HemorrhoidsFiber intake and less straining (including squatting)Weak–––Cochrane review (7 randomised trials, 378 participants): risk of persisting symptoms 'decreased by 53% in the fiber group (RR 0.47, 95% CI 0.32 to 0.68)'. A 2019 review: 'A low-fiber diet and constipation have historically been thought to increase the risk for hemorrhoids, but not proven'; symptoms were 'equally reported by patients with and without hemorrhoids'; nearly 4 million U.S. office and emergency department visits annually. Sikirov 2003 (28 volunteers): squatting needed far less straining and time than sitting (P < 0.0001).1. Cochrane Database of Systematic Reviews
    2. Clinical Gastroenterology and Hepatology
    3. Digestive Diseases and Sciences
    AppendicitisWesternized, low-fiber diet and sanitation (Burkitt's idea)Weak–South Korea, Chile, Turkey–GBD 2021 (Lancet Gastroenterol Hepatol 2024): age-standardised incidence 364 per 100,000 in high-income Asia Pacific vs 81.4 per 100,000 in western sub-Saharan Africa; global 214 per 100,000 (2021). Ferris et al., Annals of Surgery 2017: pooled 21st-century incidence South Korea 206, Chile 202, Turkey 160 per 100,000 person-years vs Northern America 100; data from newly industrialized countries 'sparse' but suggest rapid rise.1. The Lancet Gastroenterology & Hepatology
    2. Annals of Surgery
    Chronic constipationToilet posture (squat vs sit) and fiber intakeWeak–––2026 meta-analysis (128 studies, 44 countries, 459,061 participants): global pooled prevalence of functional constipation 12.14% (95% CI 11.14-13.23); 14.60% in females vs 10.62% in males; 19.89% in older people. Portugal, Rome IV survey (2022, n=1,335): chronic constipation 17.8%, made up of functional constipation 9.3% and constipation-type irritable bowel syndrome 8.5%. 2025 scoping review of 42 studies: 'Squatting may reduce digestive strain and enhance bowel evacuation, potentially benefiting constipation' but methodological limitations 'preclude definitive conclusions'.1. Clinical and Translational Gastroenterology
    2. United European Gastroenterology Journal
    3. BMC Public Health
    Inflammatory bowel disease (Crohn's disease and ulcerative colitis)Westernizing lifestyle during industrialization (diet, hygiene, environment) - cause unknownWeakBrazilNorway, Germany, United States, Canada–Ng et al., Lancet 2017 (147 population-based studies): highest prevalence in Norway (ulcerative colitis 505 per 100,000), Germany (Crohn's 322 per 100,000), USA (UC 286) and Canada (Crohn's 319); 16 of 22 Crohn's and 15 of 18 UC studies in North America and Europe reported stable or decreasing incidence. Since 1990 new cases rising each year in Brazil (Crohn's +11.1%, UC +14.9%) and Taiwan (+4.0%, +4.8%). Brazil public health system 2012-2020: new IBD cases roughly flat (9.4 to 9.6 per 100,000 a year), but the number living with IBD rose from 30.0 to 100.1 per 100,000 (0.1% of Brazilians in 2020), vs more than 0.3% in North America, Oceania and many European countries.1. The Lancet
    2. The Lancet Regional Health - Americas
    Stomach (gastric) cancerMoving from Japan to the U.S. and changing diet and environment over generationsModerate–––Multiethnic Cohort Study, Hawaii and California (94,232 people, 716 stomach cancers), compared with non-Hispanic whites and adjusted for diet and lifestyle: Japan-born first generation had about 4.6 times the risk (hazard ratio 4.62, 95% CI 3.24-6.59); U.S.-born second generation about 3.7 times (both parents Japan-born, HR 3.66) or 3.4 times (one parent Japan-born, HR 3.39); third generation about 2.6 times (HR 2.57, 95% CI 1.93-3.42).1. Cancer Causes & Control
    Coronary artery disease (calcium in heart arteries)Forager-farmer life: active outdoor work, low-fat high-fiber diet, little smokingModerate–United StatesBoliviaLancet 2017, 705 Tsimane adults aged 40 and older: 85% had no coronary artery calcium, 13% had scores of 1 to 100, and 3% had scores above 100 (the level counted as significant artery disease). Among people over 75, 65% had no calcium and only 8% had scores of 100 or more, about five times less common than in the US MESA study. This was despite 51% having raised blood markers of inflammation.1. The Lancet
    Heart disease and strokeTraditional island diet with almost no Western food, root vegetables and fish, very lean bodiesWeak––Papua New Guinea, SwedenJ Intern Med 1994, 151 men and 69 women aged 14 to 87: all Kitavans aged 40 and older had diastolic pressure below the Swedish median; total cholesterol, LDL and apolipoprotein B were 10-30% lower in Kitavan men 40+ and women 60+; about 76% of men and 80% of women over 20 smoked.1. Journal of Internal Medicine
    2. Thrombosis and Haemostasis
    High blood pressureVery low salt intake from lifelong traditional dietStrong––BrazilINTERSALT 1988, 10,079 adults aged 20-59 in 52 centres: 24-hour urinary sodium ranged from 0.2 mmol (Yanomamo Indians, Brazil) to 242 mmol (north China). Four very-low-sodium centres had low blood pressure and little or no rise with age. In the other 48 centres, sodium was related to the age slope of blood pressure but not to median blood pressure or the prevalence of high blood pressure. Yanomamo study 1989: 195 people, none hypertensive. DASH-Sodium trial 2001 (412 adults, 30 days on each salt level): on a typical U.S. diet, cutting salt from high to medium lowered systolic (top-number) blood pressure by 2.1 mmHg, and from medium to low by a further 4.6 mmHg.1. BMJ
    2. Journal of Human Hypertension
    3. New England Journal of Medicine
    Heart attack, stroke and cardiovascular deathMediterranean diet with extra-virgin olive oil or nutsModerate––SpainNEJM 2018 republication, 7,447 adults aged 55-80, median follow-up 4.8 years: 288 events. Olive oil group 96 (3.8%), nuts group 83 (3.4%), control 109 (4.4%). Adjusted hazard ratios vs control: 0.69 (95% CI 0.53-0.91) olive oil, 0.72 (0.54-0.95) nuts. Results were similar after excluding 1,588 participants whose assignment may have departed from the protocol.1. New England Journal of Medicine
    Coronary heart diseaseTraditional Japanese diet and lifestyle (and what happens when Japanese people move to the US)ModerateJapanUnited States, United Kingdom–WHO age-standardized ischaemic heart disease death rate per 100,000, both sexes, 2004: Japan 32.1, UK 90.1, USA 97.6. Ni-Hon-San: age-adjusted 2-year incidence of definite CHD per 1,000 person-years was 1.4 in Japan, 3.0 in Hawaii and 4.3 in California. Japan's CHD mortality in the 50-69 birth cohort was more than 67% lower in men and more than 75% lower in women than in the USA (Int J Epidemiol 2015).1. WHO Global Health Observatory
    2. International Journal of Epidemiology
    3. National Research Council
    Type 2 diabetes and obesityTraditional active farming life versus a Western environmentModerate––Mexico, United StatesDiabetes Care 2006, age- and sex-adjusted type 2 diabetes: 6.9% in Mexican Pima, 38% in US (Arizona) Pima, 2.6% in non-Pima Mexicans. Obesity in Mexican Pima: 7% of men and 20% of women (non-Pima Mexicans 9% of men, 27% of women).1. Diabetes Care
    Type 2 diabetesBody weight and fat distribution (South Asian ancestry), not a lifestyle habitModerateUnited KingdomIndia, Pakistan, Bangladesh–Lancet Diabetes Endocrinol 2021, 1,472,819 adults in England (75,956 South Asian): the BMI equal in diabetes risk to BMI 30.0 in White adults was 23.9 kg/m2 (95% CI 23.6-24.0) for South Asian adults. WHO 2022 age-standardized estimates, adults 18+: diabetes India 22.6%, Pakistan 30.9%, Bangladesh 17.9%, UK 8.8%; obesity (BMI 30+) India 7.2%, Pakistan 22.4%, Bangladesh 5.1%, UK 27.0%.1. The Lancet Diabetes & Endocrinology
    2. WHO Global Health Observatory
    3. WHO Global Health Observatory
    Obesity and type 2 diabetesShift from traditional food and work to imported processed food and low activityWeakJapanNauru, Tonga–WHO 2022 age-standardized adult obesity (BMI 30+), both sexes: Tonga 72.1% (95% range 68.3-75.6), Nauru 70.8% (67.8-73.7), USA 40.4%, Japan 5.5%. Adult diabetes (18+): Nauru 25.3%, Tonga 23.4%. A 2004 Nauru survey of 1,592 people aged 15-64 found diabetes in 13.7% overall, rising from 4.5% at ages 15-24 to 42.7% at ages 55-64.1. WHO Global Health Observatory
    2. WHO Global Health Observatory
    3. BMC Public Health
    Type 2 diabetesMoving from a subsistence atoll life to urban New ZealandModerate––Tokelau, New ZealandDiabetologia 1989, Tokelau Island Migrant Study 1968-1982: age-standardised diabetes prevalence per 100 rose from 7.5 to 10.8 in migrant men and 11.7 to 19.9 in migrant women, versus 3.0 to 7.0 in men and 8.7 to 14.3 in women who stayed. Incidence relative risk in migrants was 1.5 for men and 1.9 for women.1. Diabetologia
    Coronary heart diseaseEating butter, cheese and drinking red wine ('French paradox')MythFranceUnited Kingdom, United States–WHO ischaemic heart disease death rate per 100,000 (age-standardized, both sexes, 2004): France 38.0, UK 90.1, USA 97.6. MONICA coronary events in men aged 35-64, 1985-95 (per 100,000, as reported in a BMJ 2000 letter): three French regions about 274, Barcelona about 210, Belfast about 695, Glasgow about 777.1. WHO Global Health Observatory
    2. BMJ
    3. BMJ
    Coronary heart diseaseTraditional Inuit diet of seal, whale and fish (omega-3 'Eskimo diet')Myth–––Can J Cardiol 2014 review (paraphrased from the abstract): the original 1970s Bang and Dyerberg studies did not measure coronary artery disease prevalence, and the review of 40 years of literature found Greenland Eskimos and Canadian and Alaskan Inuit have coronary artery disease about as often as non-Eskimo populations.1. Canadian Journal of Cardiology
    Stomach (gastric) cancerTraditional salt-preserved and pickled foods, plus widespread childhood H. pylori infectionStrongUnited States, IndiaMongolia, Japan, South Korea, Iran–GLOBOCAN 2022 age-standardised incidence per 100,000, both sexes (as tabulated by WCRF): Mongolia 35.5, Japan 27.6, South Korea 27.0, Iran 19.4, India 4.5, US 4.1, World 9.2. IARC/Plummer 2015: worldwide, 89.0% of non-cardia gastric cancer is attributable to H. pylori. Meta-analysis of 26 prospective cohorts (4,956,350 people): high salt intake RR 1.25 (95% CI 1.10-1.41); high pickled-food intake RR 1.28 (1.05-1.57); salted fish RR 1.14 (0.95-1.36, not significant). Korean placebo-controlled trial in 1,676 first-degree relatives of patients: gastric cancer in 1.2% (10/832) after H. pylori treatment vs 2.7% (23/844) on placebo over a median 9.2 years (HR 0.45, 95% CI 0.21-0.94).1. World Cancer Research Fund (GLOBOCAN 2022 figures)
    2. International Journal of Cancer
    3. Frontiers in Nutrition
    4. New England Journal of Medicine
    Stomach (gastric) cancerHome refrigeration replacing salting and pickling (with less H. pylori)Weak––Japan, South KoreaGBD 2021 modelled age-standardised incidence per 100,000, 1990 to 2021: Japan 64.05 to 25.54; South Korea 71.18 to 25.76; global 24.76 to 14.33. Meta-analysis of 12 observational studies (14,361 people): refrigerator use and gastric cancer, pooled OR 0.70 (95% CI 0.56-0.88); in some Asian countries OR 0.68 (0.50-0.93), but not in some Western countries such as Germany. Japanese in Hawaii vs Japan, 1960-1997 (Cancer Incidence in Five Continents): migration led to lower risk of stomach cancer.1. BMC Cancer
    2. PLoS One
    3. Ethnicity & Disease
    Breast cancerTraditional East Asian lifestyle versus Western lifestyle after moving to the USModerateChina, IndiaUnited States, United Kingdom–GLOBOCAN 2022 age-standardised incidence per 100,000 women (as tabulated by WCRF): US 95.9, UK 94.0, Germany 77.0, Japan 74.4, World 46.8, China 33.0, India 26.6. Ziegler 1993 (597 cases, 966 controls, Chinese/Japanese/Filipino women aged 20-55 in California and Hawaii): Asian-American women born in the West had a breast cancer risk 60% higher than those born in the East; migrants who had lived in the West a decade or longer had a risk 80% higher than recent migrants. Abubakar 2026 (registry data): annual incidence increases of 5.3% in native Koreans and 3.8% in native Japanese vs stable or declining in US White women.1. World Cancer Research Fund (GLOBOCAN 2022 figures)
    2. Journal of the National Cancer Institute
    3. Cancer Epidemiology, Biomarkers & Prevention
    Breast cancerEating soy foods (tofu, miso, soy milk) regularlyWeak–––Meta-analysis of 35 studies (Chen 2014): high vs low soy isoflavone intake, Asian studies OR 0.59 (95% CI 0.48-0.69) premenopausal and OR 0.59 (0.44-0.74) postmenopausal; Western postmenopausal women OR 0.92 (0.83-1.00), not significant once study design was accounted for. Chinese meta-analysis of 28 studies (Zhong 2012): overall pooled OR 0.86 (0.78-0.94), but protection seen only in case-control studies, not cohort studies.1. PLoS One
    2. Wei Sheng Yan Jiu
    Breast cancerLonger lifetime breastfeeding (and more births)Strong–––Collaborative Group on Hormonal Factors in Breast Cancer, 47 studies in 30 countries (50,302 women with breast cancer, 96,973 without): relative risk fell 4.3% (95% CI 2.9-5.8) for every 12 months of breastfeeding, plus 7.0% (5.0-9.0) for each birth. Estimated cumulative incidence by age 70 in developed countries would fall from 6.3 to 2.7 per 100 women with the births and breastfeeding typical of developing countries until recently; breastfeeding could account for almost two-thirds of that reduction.1. The Lancet
    Prostate cancerTraditional Japanese lifestyle versus Western lifestyle (and PSA screening)WeakChina, IndiaUnited States, Lithuania, Norway, Sweden–GLOBOCAN 2022 age-standardised incidence per 100,000 (as tabulated by WCRF): US 75.2, Japan 50.1, World 29.4, China 9.7, India 5.6; among the highest are Lithuania 135.0, Norway 109.9 and Sweden 104.3 (the French territories Guadeloupe 157.5 and Martinique 134.3 are also in the top five). Shimizu 1991 (Los Angeles County): prostate incidence was much higher than in the homelands for each group studied, and rates of immigrants were similar to US-born patients in the Japanese population, regardless of age at immigration. Wada 2026: population-based organised PSA screening is implemented in 80% of Japanese municipalities.1. World Cancer Research Fund (GLOBOCAN 2022 figures)
    2. British Journal of Cancer
    3. Scientific Reports
    Esophageal squamous cell cancerDrinking tea very hot, soon after pouringModerate––Iran, China, TurkeyGolestan Cohort Study (50,045 people aged 40-75, median 10.1 years of follow-up, 317 new cases): objectively measured tea temperature of 60 degrees C or more vs under 60 degrees C, HR 1.41 (95% CI 1.10-1.81); reported preference for 'very hot' vs cold/lukewarm, HR 2.41 (1.27-4.56); drinking within 2 minutes of pouring vs 6 or more minutes, HR 1.51 (1.01-2.26). Earlier Golestan case-control study (300 cases, 571 controls) as described in Arch Iran Med: very hot tea adjusted OR 8.16 (95% CI 3.93-16.91), hot tea OR 2.07 (1.28-3.35). IARC 2016: very hot beverages are Group 2A, probably carcinogenic; 'very hot' means above 65 degrees C.1. International Journal of Cancer
    2. IARC / WHO
    3. Archives of Iranian Medicine
    Cancer in general (coffee scare)Drinking coffeeMyth–––IARC press release, 15 June 2016: drinking coffee was 'not classifiable as to its carcinogenicity to humans (Group 3)', previously Group 2B in 1991, after review of more than 1000 studies in humans and animals. 'Reduced risks were seen for cancers of the liver and uterine endometrium.' Very hot beverages (above 65 degrees C) were classified Group 2A.1. IARC / WHO
    2. The Lancet Oncology
    Nasopharyngeal cancer (cancer at the back of the nose)Eating Chinese-style salted fish, especially in childhoodModerate–China–IARC Monographs Volume 56 (1993): Chinese-style salted fish is Group 1, carcinogenic to humans; eight case-control studies consistently showed a strong relationship with nasopharyngeal carcinoma, with a significant dose-response and an association 'especially strong for intake of salted fish during childhood'. Dose-response meta-analysis (Lian 2022): salted fish summary RR 1.23 (95% CI 1.04-1.47) for low intake and 1.45 (1.19-1.76) for high intake. GLOBOCAN fact sheet (labelled GLOBOCAN 2024): 119,750 new nasopharynx cases worldwide, ASR (world) 1.3 per 100,000, with Asia 97,008 cases (81.0%).1. IARC via INCHEM
    2. European Archives of Oto-Rhino-Laryngology
    3. IARC Global Cancer Observatory
    Liver cancer (hepatocellular carcinoma)Hepatitis B vaccination of all newborns (Taiwan, from July 1984)Strong––TaiwanChang 1997 (Taiwan National Cancer Registry): average annual incidence of hepatocellular carcinoma in children aged 6 to 14 fell from 0.70 per 100,000 (1981-1986) to 0.57 (1986-1990) to 0.36 (1990-1994), P<0.01. Chang 2009 (1,958 patients aged 6-29, 1983-2004): among children aged 6-19, 64 cases in 37,709,304 person-years among vaccinated vs 444 cases in 78,496,406 person-years among unvaccinated, age- and sex-adjusted relative risk 0.31 for those vaccinated at birth (P<.001). Among vaccinated people, risk was higher with incomplete vaccination (OR 4.32) and with a hepatitis B-positive mother (OR 29.50).1. New England Journal of Medicine
    2. Journal of the National Cancer Institute
    Liver cancer (hepatocellular carcinoma)Chronic viral hepatitis (B, C, D) and food contaminated with aflatoxin mold toxinModerateUnited StatesMongolia, China–Liver cancer age-standardised incidence per 100,000, 2022 (WCRF): Mongolia 96.1, Egypt 32.0, China 15.0, Japan 9.2, World 8.6, US 6.8. Kurbanov 2007: in Mongolia, general-population seroprevalence of hepatitis B about 10% and hepatitis C about 15%, and 75-100% of hepatitis B-infected people are co-infected with hepatitis delta. Liu & Wu 2010: of 550,000-600,000 new liver cancer cases worldwide each year, about 25,200-155,000 may be attributable to aflatoxin (4.6-28.2%), mostly in sub-Saharan Africa, Southeast Asia and China.1. World Cancer Research Fund (2022 figures)
    2. Journal of Viral Hepatitis
    3. Environmental Health Perspectives
    Melanoma (skin cancer)Sun exposure and sunburn in fair-skinned people (and sunbed tanning)Strong–Australia, New Zealand, Denmark, Norway, Sweden–GLOBOCAN 2022 melanoma age-standardised incidence per 100,000, both sexes (WCRF): Australia 37.0, Denmark 31.1, Norway 30.6, New Zealand 29.8, Sweden 27.4, World 3.2. Women: Denmark 35.6, Norway 31.7, Australia 29.1. IARC 2025: 83% of the 331,700 melanoma cases worldwide in 2022 (about 267,000) were attributable to UV radiation; in Australia/New Zealand, northern Europe and North America more than 95%. SunSmart in Victoria is estimated to have prevented 103,000 skin cancers and 1000 deaths between 1988 and 2003.1. World Cancer Research Fund (GLOBOCAN 2022 figures)
    2. IARC / WHO
    Lung cancerCigarette smokingStrongIndiaHungary, China, United States, Japan–GLOBOCAN 2022 lung cancer age-standardised incidence per 100,000, both sexes (WCRF): Hungary 47.6, China 40.8, US 31.9, Japan 30.5, India 5.8, World 23.6. Japan men 47.2 vs women 15.8. CDC: 'In the United States, cigarette smoking is linked to about 80% of lung cancer deaths.' WHO: an estimated 2.5 million new cases and 1.8 million deaths in 2022.1. World Cancer Research Fund (GLOBOCAN 2022 figures)
    2. CDC
    3. WHO
    Lung cancerCooking and heating indoors with smoky coalModerate––ChinaHosgood 2011 meta-analysis of 25 case-control studies (10,142 cases, 13,416 controls): household coal use and lung cancer OR 2.15 (95% CI 1.61-2.89); mainland China and Taiwan OR 2.27 (1.65-3.12); southwestern China OR 2.98 (1.18-7.53). 2026 narrative review of the Wumeng Mountain region (Xuanwei/Fuyuan): coal-pollution lung cancer is 'prevalent among non-smoking women'. GLOBOCAN 2022 lung ASR per 100,000, women (WCRF): China 30.3, Japan 15.8, India 3.2.1. International Journal of Epidemiology
    2. Zhongguo Fei Ai Za Zhi
    3. World Cancer Research Fund (GLOBOCAN 2022 figures)
    Cervical cancerHPV vaccination in early adolescenceStrong–Eswatini, Zambia, Malawi, Zimbabwe, TanzaniaUnited Kingdom, Sweden, United StatesPublic Health Scotland, Jan 2024: 'no cervical cancer cases have been detected in fully vaccinated women' who received their first dose at 12-13 (programme began 2008, covers every Scottish woman eligible for screening). Lei 2020, Sweden (1,672,983 girls and women, 2006-2017): cumulative incidence 47 per 100,000 vaccinated vs 94 per 100,000 unvaccinated; incidence rate ratio 0.12 (95% CI 0.00-0.34) if vaccinated before age 17 and 0.47 (0.27-0.75) at age 17 to 30. Palmer 2026: adjusted vaccine effectiveness against CIN2+ (precancer) 72.6% (95% CI 67.7-76.8) at age 12-13. GLOBOCAN 2022 cervical ASR per 100,000 (WCRF): Eswatini 95.9, Zambia 71.5, Malawi 70.9, Zimbabwe 68.2, Tanzania 64.8, World 14.1, US 6.3.1. Public Health Scotland
    2. New England Journal of Medicine
    3. International Journal of Cancer
    4. World Cancer Research Fund (GLOBOCAN 2022 figures)
    Cervical cancerNational school HPV vaccination (both sexes) plus 5-yearly HPV-test screeningModerate––AustraliaHall 2019 (Lancet Public Health, Policy1-Cervix model): current Australian incidence 'seven cases per 100 000 women'; projected below six per 100,000 by 2020 (range 2018-22), below four per 100,000 by 2028 (range 2021-35), and below one per 100,000 by 2066 (2054-77) if 5-yearly HPV screening continues. WHO elimination strategy: 90% of girls vaccinated against HPV by age 15, 70% of women screened with a high-performance test by 35 and again by 45, 90% of women with precancer or cancer treated; elimination means 4 or fewer new cases per 100,000 women a year.1. The Lancet Public Health
    2. WHO
    Childhood asthma and allergic sensitizationTraditional (Amish) horse-and-barn farming versus industrialized (Hutterite) farmingModerate––United States"The prevalence of asthma and allergic sensitization was 4 and 6 times as low in the Amish"; median endotoxin in Amish house dust was 6.8 times as high as in Hutterite dust (Stein et al., NEJM 2016; 60 children aged 7-14, 30 Amish in Indiana and 30 Hutterite in South Dakota). Dust from Amish homes, but not Hutterite homes, protected mice from allergic asthma.1. New England Journal of Medicine
    Type 1 diabetes in childrenLiving in Finland (wealthier, cleaner, fewer childhood infections) versus neighboring Russian KareliaModerate–FinlandRussia, EstoniaAnnual age-adjusted incidence, children under 15, 1990-99: 7.4 per 100,000 (95% CI 3.5-11.3) in Russian Karelia vs 41.4 per 100,000 (37.3-45.5) in Finland; HLA-DQ risk genotype frequencies were similar in both populations (Kondrashova et al., Ann Med 2005).1. Annals of Medicine
    2. Cell
    Asthma, hay fever, eczema and allergic sensitizationLiving in Finnish Karelia versus Russian Karelia (different microbial exposure)Moderate––Finland, Russia"Asthma, hay fever, atopic eczema, self-reported rhinitis, as well as atopic sensitization, were threefold to 10-fold more common in Finland, as compared to Russian Karelia"; children 7-11 in 2003 (Finnish n = 98, Russian Karelia n = 82), followed up 2010/2012 (Ruokolainen et al., Clin Exp Allergy 2017).1. Clinical and Experimental Allergy
    Celiac diseaseLower economic status and a less sanitized environment (Russian Karelia) versus FinlandWeak––Finland, Russia"Transglutaminase antibodies were less frequent in Russian Karelia than in Finland (0.6% versus 1.4%, P = 0.005)"; celiac confirmed by biopsy in 4 of 8 antibody-positive Karelian children, about 1 in 496 in Karelia vs 1 in 107 in Finland; 1,988 Karelian and 3,654 Finnish schoolchildren (Kondrashova et al., Ann Med 2008).1. Annals of Medicine
    Peanut allergyFeeding infants peanut snacks (such as Bamba) early versus avoiding peanut in the first yearModerate––Israel, United KingdomPeanut allergy prevalence 1.85% in UK vs 0.17% in Israeli schoolchildren (5,171 UK and 5,615 Israeli children); adjusted risk ratio 9.8 (95% CI 3.1-30.5). At 8-14 months, Israeli infants ate a median 7.1 g of peanut protein per month vs 0 g for UK infants (77 UK and 99 Israeli infants) (Du Toit et al., J Allergy Clin Immunol 2008).1. Journal of Allergy and Clinical Immunology
    Peanut allergyEating peanut regularly from infancy (4 to 11 months) instead of avoiding itStrong–––640 infants with severe eczema, egg allergy, or both randomized to eat or avoid peanut until 60 months. Among 530 with negative skin tests: peanut allergy 13.7% (avoidance) vs 1.9% (consumption), P<0.001. Among 98 with positive skin tests: 35.3% vs 10.6%, P=0.004 (Du Toit et al., NEJM 2015, LEAP trial).1. New England Journal of Medicine
    Multiple sclerosisLiving far from the equator (less sunlight, less vitamin D from skin)Moderate–––A meta-analysis of 650 prevalence estimates from 321 studies found MS prevalence (adjusted for age) rose with each degree of distance from the equator: by 1.04 per degree, or 2.60 per degree after accounting for the year each study was done. The rise flattened at high latitudes (Simpson et al., J Neurol Neurosurg Psychiatry 2011).1. Journal of Neurology, Neurosurgery and Psychiatry
    2. Science
    Multiple sclerosisTraditional Norwegian fish and cod-liver-oil diet (vitamin D despite weak sun)Weak–Norway–Across latitudes 58 to 71 degrees N, crude MS prevalence was 203 per 100,000 as of 1 January 2012, with no latitude gradient (Berg-Hansen et al., Mult Scler 2014).1. Multiple Sclerosis Journal
    2. Neuroepidemiology
    Multiple sclerosisInuit ancestry and traditional Arctic life (often linked to a marine diet)WeakGreenland––In 2014, 7 people were living with MS in Greenland (12.52 per 100,000), and 22 new cases were recorded from 1973 to 2014 (0.97 per 100,000 people per year). Inuit in Greenland had about 2% of the MS risk of non-Inuit Danes. Counting extra diagnoses from hospital registers raised Greenland's 2014 figure to 48.29 per 100,000, still well below Denmark (Nielsen et al., Mult Scler Relat Disord 2025).1. Multiple Sclerosis and Related Disorders
    Multiple sclerosisTaking high-dose vitamin D supplements to prevent or slow MSWeak–––A genetic study of up to 14,498 people with MS and 24,091 without found that people whose genes give them lower vitamin D had about twice the odds of MS (Mokry et al., PLoS Med 2015). In the D-Lay MS trial (316 adults after a first MS-like episode, 100,000 IU every 2 weeks for 2 years), 60.3% on vitamin D vs 74.1% on placebo showed new disease activity, mostly on MRI scans, but relapses were not significantly fewer (JAMA 2025). In the PrevANZ trial (199 people analysed), 1,000, 5,000 or 10,000 IU a day did not reduce progression to MS (Brain 2024).1. PLoS Medicine
    2. JAMA
    3. Brain
    Type 1 diabetes in children and teensLiving at high northern latitude in a wealthy, low-infection country (cause unknown)Weak–Finland–Pooled incidence in under-20s, 2000-2022: 56.81 per 100,000 person-years (95% CI 55.91-57.73) in Finland vs global pooled 14.07 (95% CI 12.15-16.29); high-income North America 28.77 (95% CI 26.59-31.13) (Hormazabal-Aguayo et al., Diabetes Metab Res Rev 2024; 126 studies, 55 countries).1. Diabetes/Metabolism Research and Reviews
    Celiac diseaseA bread-heavy, gluten-rich diet in a community whose eating habits changed recentlyWeak–––Among 989 Saharawi refugee children, 5.6% tested positive for celiac antibodies, and gut biopsies in a subsample confirmed the test (Catassi et al., Lancet 1999). A 2015 review calls this the highest celiac prevalence described anywhere, compared with about 1% in Europe and the USA. Bread and other gluten-containing foods were the children's staple diet (Ratsch and Catassi, Bull WHO 2001).1. Bulletin of the World Health Organization
    2. The Lancet
    3. Tissue Antigens
    4. Digestive Diseases
    Childhood asthma, hay fever and atopyGrowing up on a farm (animal sheds, raw farm milk, varied household microbes)Moderate–––Greater microbial diversity in children's rooms was linked to lower asthma: OR 0.62 (95% CI 0.44-0.89) in PARSIFAL and OR 0.86 (95% CI 0.75-0.99) in GABRIELA (Ege et al., NEJM 2011). In the PASTURE birth cohort (n = 769), farm children had half the hay fever risk at age 10.5 (aOR 0.50; 95% CI 0.31-0.79); the farm milk benefit (aOR 0.35; 95% CI 0.17-0.72) required continuous consumption (Pechlivanis et al., JACI In Practice 2023).1. New England Journal of Medicine
    2. Journal of Allergy and Clinical Immunology: In Practice
    Allergic disease and autoimmunity"Being too clean" (hand washing, home cleaning) as the cause of allergiesMyth–––Strachan's 1989 study found that British children from larger families were less likely to get hay fever. Perkin and Strachan (2022) wrote that many microbial and lifestyle factors have been studied since, but none robustly explains the family-size and farming effects. Bloomfield et al. (2016), an expert-panel review, found "no good evidence" that hygiene as the public understands it is responsible for the changes in microbial exposure behind allergy.1. BMJ
    2. Frontiers in Allergy
    3. Perspectives in Public Health
    Childhood asthma and eczema (atopic dermatitis)Having a dog in the home during the first year of lifeWeak––SwedenSweden, 1,011,051 children born 2001-2010: dog exposure in the first year was linked to lower asthma at school age (OR 0.87; 95% CI 0.81-0.93) but not under 3 years of age (HR 1.03; 95% CI 1.00-1.07) (Fall et al., JAMA Pediatrics 2015). Meta-analysis of 21 birth cohorts: pooled RR for eczema 0.72 for dogs (95% CI 0.61-0.85; 15 studies), 0.94 for cats (95% CI 0.76-1.16) (Pelucchi et al., JACI 2013).1. JAMA Pediatrics
    2. Journal of Allergy and Clinical Immunology
    Eczema (atopic dermatitis)Moisturizing a newborn's skin daily to prevent eczemaMyth–––1,394 newborns with a family history of allergic disease randomized to daily emollient or standard care: eczema at age 2 in 139 of 598 (23%) vs 150 of 612 (25%); adjusted RR 0.95 (95% CI 0.78-1.16), p=0.61. Skin infections in year 1: adjusted incidence rate ratio 1.55 (95% CI 1.15-2.09) (Chalmers et al., Lancet 2020, BEEP trial).1. The Lancet
    Goiter and iodine deficiency disordersUsing iodized saltStrongSwitzerland, Sri Lanka, India, NigeriaBurundi, Mozambique, Madagascar–Sri Lanka, 16,910 schoolchildren aged 6-12: goitre on palpation fell from 18.6% to 2.1% across national surveys after universal salt iodisation began in 1995 (surveys 2000-2016). Worldwide in 2020, 88% of people use iodized salt; the number of countries with insufficient iodine fell from 113 in 1993 to 21 in 2021 (Iodine Global Network). As of 2020 Burundi, Mozambique and Madagascar remained mild-to-moderately deficient; Nigeria and India are iodine-sufficient with 93% iodized-salt coverage.1. Nutrients
    2. European Journal of Endocrinology
    3. Iodine Global Network
    4. The Journal of Nutrition
    5. Historical Dictionary of Switzerland
    Kidney stonesLiving in a hot climate (more sweating, more concentrated urine)Moderate––United StatesCancer Prevention Study II (1,185,124 adults aged 30+, recruited 1982): age-adjusted prevalence among white men was 14.9 (95% CI 14.2-15.7) in North Carolina vs 5.6 (4.7-6.4) in North Dakota; among women, 6.4 (5.8-6.9) in South Carolina vs 2.4 (1.9-2.9) in South Dakota. A 2008 PNAS model projected the share of Americans living in high-risk zones to grow from 40% in 2000 to 56% by 2050 under warming.1. Kidney International
    2. Proceedings of the National Academy of Sciences
    3. Open Research Europe
    4. European Urology
    Recurrent kidney stonesDrinking extra water (about 2 litres or more per day)Weak–––1996 randomised trial (99 on 2+ L/day vs 100 usual care, 5 years): recurrence 12.1% vs 27% (p=0.008). 2026 Lancet randomised trial (1,658 people at six US centres, 2-year follow-up): symptomatic stone events in 154 (19%) of 826 in the intervention group vs 165 (20%) of 832 controls (hazard ratio 0.96, 95% CI 0.77-1.20).1. BMC Urology
    2. The Lancet
    GoutSugary drinks, alcohol and purine-rich food on top of inherited riskModerate–New Zealand–National data for 2009 (n = 4,295,296): all-ages crude prevalence of diagnosed gout 2.69%; relative risk 3.11 for Maori and 3.59 for Pacific people; prevalence in elderly Maori and Pacific men 'particularly high at >25%'. Separately, in 46,393 US men followed 12 years, 2 or more sugar-sweetened soft drinks a day gave a gout relative risk of 1.85 (95% CI 1.08-3.16) vs less than one a month.1. Rheumatology
    2. BMJ
    3. Annals of Human Genetics
    Lactose intolerance (lactase non-persistence)Long history of dairy herding and drinking milk as adultsStrong–Greenland–Keeping the ability to digest milk sugar into adulthood is common in people of European ancestry and in some African, Middle Eastern and South Asian groups, but rare or absent elsewhere (Itan et al., BMC Evol Biol 2010). In Greenland (535 people tested), 88.5% of Inuit had lost it, compared with 7.5% of people of Scandinavian ancestry (2023). In central Sweden, gene tests suggest only about 7-9% of white adults and schoolchildren lose it (2007).1. Scandinavian Journal of Gastroenterology
    2. BMC Evolutionary Biology
    3. Scandinavian Journal of Gastroenterology
    4. European Journal of Nutrition
    Vitamin D deficiency and ricketsEating oily fish and fortified foods, versus relying on sunlight aloneModerateSwedenSaudi Arabia–ECTS position statement (2019): vitamin D deficiency (25(OH)D under 50 nmol/L) occurs in under 20% of the population in Northern Europe, in 30-60% in Western, Southern and Eastern Europe, and up to 80% in Middle East countries. Saudi Arabia: pooled deficiency 63.5% (95% CI 53.3-73.7) across 16 studies and 20,787 adults. Sweden after expanding mandatory fortification in 2018: none of the 18-month-olds and 4-year-olds with blood tests (n = 281 and 270) were deficient (under 30 nmol/L).1. European Journal of Endocrinology
    2. Nutrients
    3. Journal of Family & Community Medicine
    4. Nutrition Journal
    5. Hormone Research in Paediatrics
    Alcohol-related liver cirrhosisLittle or no alcohol drinking (as in several Muslim-majority countries)StrongKuwait, Libya, Saudi Arabia, AfghanistanCzechia, Germany, France, Hungary–WHO Global Health Observatory, 2019, adults 15+: alcohol-attributable fraction of liver cirrhosis deaths Kuwait 1.8% (95% UI 0.5-5.4), Libya 3.6% (1.3-9.2), Afghanistan 4.2% (1.6-9.7), Saudi Arabia 4.7% (1.5-11.4) vs Czechia 74.4% (65.4-80.7), Germany 71.9% (61.6-79.2), France 71.2% (60.1-78.3), Hungary 70.5% (59.1-78.6). Alcohol per person aged 15+ (litres pure alcohol, 2019): Kuwait 0.1, Libya 0.0, Czechia 13.9.1. WHO Global Health Observatory
    2. WHO Global Health Observatory
    3. The Lancet Gastroenterology & Hepatology
    Liver cirrhosis (all causes)Living in a country where almost nobody drinks (assumed to mean little liver cirrhosis)MythIceland, Norway, Israel, Singapore, JapanEgypt, Pakistan, Indonesia, Saudi Arabia, Afghanistan–WHO Global Health Observatory, 2019, age-standardised cirrhosis death rate per 100,000 adults 15+: Egypt 126.1, Indonesia 54.1, Pakistan 50.8, Saudi Arabia 36.3, Afghanistan 35.4 (alcohol per person aged 15+: Egypt 0.1, Indonesia 0.1, Pakistan 0.1 litres) vs Iceland 2.3 (7.9 L), Singapore 3.2 (1.9 L), Norway 3.3 (7.0 L), Israel 3.6 (4.2 L), Japan 6.5 (6.5 L), France 8.9 (12.0 L). The GBD 2017 study found Egypt had the highest cirrhosis death rate in every year from 1990 to 2017, and around 10% of Egyptians were estimated to have hepatitis C by the early 2000s. Across 179 countries in the WHO data, countries that drink more tend to have somewhat lower cirrhosis death rates (a rank correlation of -0.37, calculated for this map), because hepatitis and poverty drive cirrhosis in many low-alcohol countries.1. WHO Global Health Observatory
    2. WHO Global Health Observatory
    3. The Lancet Gastroenterology & Hepatology
    4. Pathogens
    Arsenic poisoning, cancer and heart disease deathsDrinking from shallow tube wells with natural arsenic in the groundwaterStrong–Bangladesh–Bangladesh's 2009 national survey found about 20 million people drinking water above the national arsenic limit of 50 µg/L and 45 million above the WHO guideline of 10 µg/L. That was estimated to cause about 24,000 adult deaths a year (plus perhaps 19,000 more at 10-50 µg/L), described as '1 in every 16 adult deaths'. In the Araihazar study (10,977 adults followed to 2022), as arsenic in people's urine fell after communities switched wells, each typical-sized drop went with 22% fewer deaths from chronic disease, 20% fewer cancer deaths and 23% fewer heart and stroke deaths.1. Bulletin of the World Health Organization
    2. JAMA
    3. The Lancet
    4. Bulletin of the World Health Organization
    Keshan disease (heart-muscle disease)Eating only locally grown grain from selenium-poor soilStrong–China–2018 meta-analysis of community trials (17 articles, 41 studies, 1,983,238 subjects): giving selenium supplements in endemic areas gave a pooled risk ratio of 0.14 (95% CI 0.12-0.16) for Keshan disease; protection rates were over 80% in 35 studies. In 2020 national surveillance, a north-east to south-west belt of selenium deficiency overlapped Keshan-endemic areas (weak but significant link, Moran's I = -0.047, P = 0.013).1. Biological Trace Element Research
    2. Asia Pacific Journal of Clinical Nutrition
    3. Biological Trace Element Research
    Dental fluorosis (mottled teeth) and skeletal fluorosisDrinking water naturally high in fluorideModerate–China, India, Mexico, Turkey–Cochrane review (2015): where water has 0.7 ppm fluoride, about 12% of people have tooth mottling noticeable enough to be a cosmetic concern (40 studies, 59,630 people) and about 40% have some mottling of any level (90 studies, 180,530 people). Cochrane 2024 update: since fluoride toothpaste became common, starting water fluoridation may reduce decay in children's baby teeth by only about a quarter of a tooth on average, and the estimate includes the possibility of no benefit (low certainty).1. Cochrane Database of Systematic Reviews
    2. Cochrane Database of Systematic Reviews
    3. Environmental Geochemistry and Health
    4. Scientific Reports
    5. JAMA Pediatrics
    Death from any causeEating spicy food or chili pepper several days a weekWeak––China, ItalyChina Kadoorie Biobank (199,293 men and 288,082 women aged 30-79, 3,500,004 person-years, 2004-2013): adjusted hazard ratio for death 0.86 (95% CI 0.82-0.90) for spicy food 6-7 days a week vs less than once a week. Moli-sani, Italy (22,811 adults, median 8.2 years): chili more than 4 times a week vs none/rare, hazard ratio 0.77 (0.66-0.90) for all-cause death. A 2022 meta-analysis of 14 case-control studies found a summary odds ratio of 2.71 (95% CI 1.54-4.75) for oesophageal cancer with high chili intake.1. BMJ
    2. Journal of the American College of Cardiology
    3. Frontiers in Nutrition
    Hip fractureNorthern European lifestyle (high-dairy diet, high calcium intake)WeakNigeria, South Africa, Tunisia, EcuadorDenmark, Norway, Sweden, Austria–Women, annual age-standardised incidence per 100,000: Denmark 574, Norway 563, Sweden 539, Austria 501; Nigeria 2, South Africa 20, Tunisia 58, Ecuador 73 (Kanis 2012 systematic review, 63 countries). Average national dietary calcium intake ranges from 175 to 1233 mg/day across 74 countries; Denmark 958 and Sweden 992 mg/day, against 636 in Nigeria (Balk 2017). Balk's Norway survey (1994-95) gave only 488 mg/day, and three quarters of the surveys were not nationally representative.1. Osteoporosis International
    2. Osteoporosis International
    Fracture (including hip fracture)Eating more dietary calcium, milk or dairy, or taking calcium supplementsMyth–––Systematic review: 'Dietary calcium intake is not associated with risk of fracture.' For hip fracture, 17 of 21 cohort studies of dietary calcium found no association. In 13 calcium-supplement trials (n=56,648), hip fracture risk was essentially unchanged (relative risk 0.95, 95% CI 0.76 to 1.18, meaning anywhere from 24% fewer to 18% more hip fractures). In the lowest-bias trials (four studies, n=44,505) there was no effect at any site. Participants were aged over 50.1. BMJ
    Myopia (nearsightedness)Intense schooling and little time outdoors in childhoodModerate–South Korea, SingaporeAustraliaSeoul, 19-year-old male conscripts (n=23,616, 2010): myopia 96.5%, high myopia 21.61%. Chinese-ethnicity children aged 6-7: myopia 3.3% in Sydney vs 29.1% in Singapore; outdoor time 13.75 vs 3.05 hours per week; parental myopia similar (68% vs 71%). Arctic: 'a historical low of less than 3% to more than 50% in new generations of young adults following the Second World War'.1. Investigative Ophthalmology & Visual Science
    2. Archives of Ophthalmology
    3. Ophthalmic & Physiological Optics
    Myopia (nearsightedness)More school time spent outdoorsStrong––China, TaiwanGuangzhou cluster randomised trial (12 schools, 1,903 six-year-olds): 3-year myopia incidence 30.4% with an extra 40 minutes outdoors daily vs 39.5% in control (difference -9.1%, 95% CI -14.1% to -4.1%). Taiwan (2 schools, 571 children aged 7-11, 1 year): new myopia 8.41% in the recess-outdoors school vs 17.65%. Taiwan national: reduced visual acuity rose from 34.8% (2001) to 50.0% (2011), then fell from 49.4% (2012) to 46.1% (2015).1. JAMA
    2. Ophthalmology
    3. Ophthalmology
    4. Ophthalmology
    Myopia (nearsightedness)Home confinement (less outdoor time, more screens) during COVID-19Moderate––ChinaFeicheng, China, school photoscreening of 123,535 children aged 6-13 (2015-2020): myopia prevalence in 2020 vs highest of 2015-2019 was 21.5% vs 5.7% at age 6, 26.2% vs 16.2% at age 7, 37.2% vs 27.7% at age 8; minimal differences at ages 9-13.1. JAMA Ophthalmology
    Flat feet (flatfoot) in childrenGoing barefoot or wearing open sandals instead of closed shoes in childhoodWeak––IndiaFootprints of 2,300 children aged 4-13: flat foot in 8.6% of children who used footwear vs 2.8% of those who did not (p<0.001, meaning very unlikely to be chance); most common with closed-toe shoes, less with sandals or slippers, least in the unshod. A 2022 review describes the sample as rural Indian children.1. Journal of Bone and Joint Surgery (British)
    2. Children
    3. Colombia Medica
    Low back painTraditional, rural or foraging lifestyles (assumed to protect the back)Weak–Sweden, Germany, BelgiumNigeria, China, Indonesia, Philippines, BoliviaVolinn 1997 review of point prevalence: rates are '2-4 times higher among Swedish, German, and Belgium general populations than among Nigerian, southern Chinese, Indonesian, and Filipino farmers'; higher in urban than rural low-income groups. Tsimane (Bolivia): 'Age-standardized current pain prevalence is 1.7-8.2 times higher for Tsimane than other select populations' (pain at any body site); 'Chronic low back pain is not a mismatch disease limited to post-industrialized populations.' Worldwide, about 12% of adults have low back pain on any given day and about 23% within a month (165 studies, 54 countries).1. Spine
    2. Proceedings of the Royal Society B
    3. Arthritis & Rheumatism
    Knee osteoarthritisProlonged daily squatting (a common daily posture in China)Moderate––China, United StatesBeijing Osteoarthritis Study, random sample aged 60 and over: about 40% of men and about 68% of women squatted for 1 hour or more daily at age 25. Those who had squatted 2 hours or more a day had about twice the odds of arthritis in the main knee joint compared with those who squatted under 30 minutes (2.0 in men, 2.4 in women; trends borderline, P about 0.07). Chinese women's age-adjusted excess of knee arthritis over white women in Framingham, Massachusetts fell from 14.4 to 9.5 percentage points once squatting was accounted for. Chinese men had less knee arthritis than white men.1. Arthritis & Rheumatism
    Hip osteoarthritisUnknown (possibly inherited hip shape; squatting lifestyle is only a guess)Weak––China, United StatesBeijing, 1,506 people aged 60 and over: crude radiographic hip OA 0.9% in women and 1.1% in men. Age-standardised prevalence ratio vs white US women 0.07 (SOF) and 0.22 (NHANES-I); vs white men 0.19. No symptomatic hip OA in Chinese men and 1 case in women; 35 cases were expected.1. Arthritis & Rheumatism
    Early death (all-cause mortality) in middle-aged and older adultsBeing able to sit down on and rise from the floor without hands or kneesWeak–––Brazil, 2,002 adults aged 51-80 (68% men), median follow-up 6.3 years, 159 deaths (7.9%). Compared with the best scorers (8-10 out of 10), the risk of dying was about 5.4 times as high for scores 0-3, 3.4 times for 3.5-5.5 and 1.8 times for 6-7.5, after allowing for age, sex and body weight. 'Each unit increase in SRT score conferred a 21% improvement in survival.'1. European Journal of Preventive Cardiology
    Dental caries (tooth decay)Low free-sugar intakeStrong––JapanWHO-commissioned systematic review (55 studies): '42 out of 50 of those in children and 5 out of 5 in adults reported at least one positive association between sugars and caries'; 'evidence of moderate quality showing that caries is lower when free-sugars intake is < 10% E'; the under 5% E finding was 'very low quality'. Sheiham and James 2014 (Japan data): caries appeared at sugar intakes of only 2-3% of energy once teeth had been exposed over 3 years. WHO: 'nearly 3.7 billion people' are affected by oral diseases.1. Journal of Dental Research
    2. Public Health Nutrition
    3. British Dental Journal
    4. World Health Organization
    Age-related hearing lossLiving in a very quiet, pre-industrial environmentModerate––SudanRosen 1962 (Mabaan, Sudan): per a 2025 review, 'actual age-related hearing loss in a population not exposed to loud noise is approximately only a 10 dB decrement at age 70', a loss too small to count as hearing loss. Goycoolea 1986 (90 Easter Island natives aged over 45): living in civilised societies 'has a significant negative effect on hearing; the severity is directly proportional to the years of exposure.'1. Annals of Otology, Rhinology & Laryngology
    2. Laryngoscope
    3. Journal of Exposure Science & Environmental Epidemiology
    Varicose veinsHigh-fibre traditional diet (less straining on the toilet)Weak––United KingdomEdinburgh Vein Study (1,566 adults aged 18-64): age-adjusted prevalence of trunk varices 40% in men and 32% in women. Global review: varicose vein prevalence '<1% to 73% in females and 2% to 56% in males', with 'the highest reported rates in Western countries'; diet and physical activity are 'not well documented'.1. Archives of Surgery
    2. Annals of Epidemiology
    3. Journal of Epidemiology and Community Health
    DementiaActive, forager-horticulturalist life (Tsimane and Moseten, Bolivian Amazon)Weak––Bolivia"Tsimane exhibited 5 cases of dementia (among n = 435; crude prevalence = 1.2%, 95% CI: 0.4, 2.7); Moseten, 1 case (among n = 169; crude prevalence = 0.6%, 95% CI: 0.0, 3.2), all aged ≥80 years." Age-standardized MCI prevalence was 7.7% (95% CI: 5.2, 10.3) in Tsimane and 9.8% (95% CI: 4.9, 14.6) in Moseten. Adults aged 60+, Alzheimer's & Dementia, 2022.1. Alzheimer's & Dementia (Gatz et al.; online Mar 2022, vol 19 issue 1, 2023)
    2. Europe PMC record (PMC13576163)
    Alzheimer's diseaseRural North Indian village life (mostly illiterate, farming population)Weak––India, United States"Standardized against the age distribution of the 1990 US Census, the overall incidence rate in those aged > or =65 years was 4.7 per 1000 person-years, substantially lower than the corresponding rate of 17.5 per 1000 person-years in the Monongahela Valley." (2-year prospective study, Ballabgarh, India, ages 55+; Neurology 2001)1. Neurology
    Exceptional longevity (reaching 100 or 110+)Blue Zones lifestyle (plant-heavy food, activity, community) in Sardinia, Okinawa, Ikaria, NicoyaWeak––Italy, Japan, Greece, Costa RicaNewman preprint (bioRxiv, 4 versions 2019 to Nov 2025, not peer-reviewed as of the latest version listed): "The state-specific introduction of birth certificates is associated with a 69-82% fall in the number of supercentenarian records" (United States) and "Only 18% of exhaustively validated supercentenarians have a birth certificate, falling to zero percent in the USA." Reply by Austad and Pes (The Gerontologist, 2025): "age data from these Blue Zones are valid and reliable." A 2025 scoping review found "No studies have been conducted in Loma Linda."1. bioRxiv
    2. The Gerontologist
    3. Aging and Disease
    4. UCL
    5. STAT
    Long life expectancyOkinawan moai (lifelong social support circles) and traditional lifestyleWeak––Japan"In 2002, Okinawa fell from the 4th to the 26th place in the ranking of the 47 Japanese prefectures by male life expectancy." The older generations "clearly experience a highly favourable mortality pattern, whereas the younger generations show mortality levels that are definitively higher compared to mainland Japan." (Poulain and Herm, J Intern Med 2024)1. Journal of Internal Medicine
    Death from any cause and cardiovascular diseaseHaving ikigai (a sense of a life worth living)Moderate––JapanOver 7 years' follow-up of 43,391 Japanese adults (Ohsaki Study), 3048 died; all-cause mortality for no ikigai vs ikigai: multivariate adjusted hazard ratio 1.5 (1.3-1.7); cardiovascular disease 1.6 (1.3-2.0); cancer 1.3 (1.0-1.6, not significant).1. Psychosomatic Medicine
    Sudden cardiac death and cardiovascular deathFrequent Finnish sauna bathingWeak––Finland2315 men aged 42-60, median follow-up 20.7 years: compared with 1 sauna session per week, the hazard ratio of sudden cardiac death was 0.78 (95% CI, 0.57-1.07) for 2 to 3 sessions per week and 0.37 (95% CI, 0.18-0.75) for 4 to 7 sessions per week (JAMA Intern Med 2015).1. JAMA Internal Medicine
    Dementia and Alzheimer's diseaseFrequent Finnish sauna bathingWeak––Finland2315 men, median follow-up 20.7 years, 204 dementia and 123 Alzheimer's cases: compared with 1 session per week, HR for dementia 0.78 (95% CI: 0.57-1.06) for 2-3 sessions and 0.34 (95% CI: 0.16-0.71) for 4-7 sessions; Alzheimer's 0.80 (0.53-1.20) and 0.35 (0.14-0.90) (Age and Ageing 2017).1. Age and Ageing
    Heart disease risk and long-term healthy agingHara hachi bu (eat until about 80% full)Weak––JapanWillcox review: "The nutritional data support mild caloric restriction (10-15%)." CALERIE randomized trial (218 healthy adults, 24 months, averaging 11.9% fewer calories): improvements in blood markers of heart disease risk (apolipoprotein B and the inflammation marker GlycA) and in markers of insulin resistance and type 2 diabetes risk (all P <=0.0009, very unlikely to be chance).1. Current Opinion in Clinical Nutrition and Metabolic Care
    2. EClinicalMedicine
    3. American Journal of Lifestyle Medicine
    Early death from any causeStrong social ties versus isolation and lonelinessModerate–––2010 meta-analysis: "Across 148 studies (308,849 participants), the random effects weighted average effect size was OR = 1.50" (95% CI 1.42 to 1.59) for stronger social relationships and survival. 2015 meta-analysis: social isolation OR = 1.29, loneliness OR = 1.26, living alone OR = 1.32, "29%, 26%, and 32% increased likelihood of mortality"; results consistent across gender, length of follow-up, and world region.1. PLoS Medicine
    2. Perspectives on Psychological Science
    Seasonal affective disorder (winter depression)Living far from the equator (less winter daylight)Weak–United States, Canada–"The mean prevalence of SAD is two times higher in North America compared to Europe. Over all prevalence studies, the correlation between prevalence and latitude was not significant." (literature review, J Affect Disord 1999)1. Journal of Affective Disorders
    Poor self-rated health and low well-beingSpending time in nature (the idea behind Nordic friluftsliv, outdoor life)Weak–––n = 19,806 adults in England: compared with no nature contact last week, contact of 120-179 minutes had ORs [95% CI] of Health = 1.59 [1.31-1.92] and Well-being = 1.23 [1.08-1.40] for good health/high well-being; "Positive associations peaked between 200-300 mins per week with no further gain." (Sci Rep 2019)1. Scientific Reports
    Short sleepPre-industrial living (no electric light): Hadza, San, TsimaneMyth–––"Sleep periods, the times from onset to offset, averaged 6.9-8.5 hr, with sleep durations of 5.7-7.1 hr, amounts near the low end of those industrial societies." Three groups: Hadza (Tanzania), San (Namibia), Tsimane (Bolivia) (Curr Biol 2015).1. Current Biology
    Major depressive episodeJapanese culture and social setting (possibly also how depression is reported)WeakJapanFrance, United States, Netherlands, New Zealand–Lifetime prevalence of DSM-IV major depressive episode: Japan 6.6 ± 0.5%, France 21.0 ± 1.1%; 12-month prevalence ranged from 2.2% (Japan) to 10.4% (Brazil). Screen-positive rates "ranged widely, from <30% in Japan and Pondicherry (India) to ≥ 60% in France, New Zealand, the USA, Brazil and Ukraine." 89,037 adults in 18 countries (BMC Med 2011).1. BMC Medicine
    Death from heart disease and from all causesDrinking green tea every day (5+ cups)Moderate––JapanOhsaki cohort, 40,530 Japanese adults aged 40-79, followed up to 11 years: all-cause mortality HR 0.77 (95% CI 0.67-0.89) in women and 0.88 (0.79-0.98) in men for 5+ cups/day vs under 1 cup/day. Women's cardiovascular mortality HR 0.69 (0.53-0.90). Source conclusion: 'but not with reduced mortality due to cancer'.1. JAMA
    Death from heart disease and from all causesEating fermented soy (natto, miso) but not other soyModerate––JapanJPHC cohort, 92,915 Japanese adults aged 45-74, 14.8 years, 13,303 deaths: fermented soy (natto and miso), highest vs lowest fifth, all-cause HR 0.90 (95% CI 0.83-0.97) in men and 0.89 (0.80-0.98) in women. Total soy HR 0.98 (0.91-1.06) men, 0.98 (0.89-1.08) women. Natto inversely linked to cardiovascular death in both sexes (HR not given in abstract).1. BMJ
    2. Frontiers in Nutrition
    Blood pressure, blood sugar and blood fats (cardiometabolic risk)Eating fermented kimchi regularlyWeak–––Meta-analysis of 5 intervention studies (205 participants) and 4 prospective cohorts (42,455 participants): fasting glucose WMD -1.93 mg/dL (95% CI -3.82 to -0.03); after excluding heterogeneous studies, triglycerides -28.9 mg/dL (-53.2 to -4.5), systolic BP -3.48 mmHg (-5.95 to -1.01).1. Nutrition Reviews
    2. Epidemiology and Health
    Death from any cause, heart disease and cancerEating a handful of nuts most daysModerate––United States, SpainNurses' Health Study (76,464 women) and Health Professionals Follow-up Study (42,498 men), 3,038,853 person-years, 27,429 deaths: pooled HR 0.80 (95% CI 0.73-0.86) for 7+ times/week, 0.87 (0.83-0.90) for 2-4 times/week, vs no nuts. PREDIMED, a Spanish trial of 7,447 adults at high heart risk: a Mediterranean diet with added nuts, compared with low-fat diet advice, had HR 0.72 (0.54-0.95) for major cardiovascular events (heart attack, stroke or cardiovascular death).1. New England Journal of Medicine
    2. New England Journal of Medicine
    Death from any cause, heart disease and cancerCycling to workModerate––Denmark, United KingdomUK Biobank, 263,450 adults, median 5.0 years: cycle commuting vs car/public transport, all-cause mortality HR 0.59 (95% CI 0.42-0.83), cardiovascular mortality 0.48 (0.25-0.92), cancer mortality 0.60 (0.40-0.90). Copenhagen (13,375 women and 17,265 men, mean 14.5 years): 'Bicycling to work decreased risk of mortality in approximately 40%' after adjustment.1. BMJ
    2. Archives of Internal Medicine
    Early death from any causeWalking 10,000 steps a dayMyth–––Lee et al., 16,741 US women (mean age 72), 4.3 years: quartile medians 2,718 / 4,363 / 5,905 / 8,442 steps/day had mortality HR 1.00 / 0.59 / 0.54 / 0.42; risk 'leveled' at approximately 7,500 steps/day. Paluch et al., 15 cohorts, 47,471 adults: HR 0.60 (95% CI 0.51-0.71) at a median of 5,801 steps vs 3,553; 0.47 (0.39-0.57) at 10,901. Benefit rose until 6,000-8,000 steps (age 60+) or 8,000-10,000 (under 60).1. JAMA Internal Medicine
    2. Lancet Public Health
    3. Popular Science
    Body weightRamadan fasting (no food or drink in daylight for a month)Weak–––Meta-analysis of 35 studies of healthy adults: weight change -1.24 kg (95% CI -1.60 to -0.88) during Ramadan; weight loss 'lasted no longer than 2 weeks after Ramadan'. Most studies were in West Asia (19), Africa (7), East Asia (3), North America/Europe (4).1. Public Health Nutrition
    Weight lossEating only in an 8-hour window (16:8 fasting)Weak–––TREAT randomized trial, 116 US adults (BMI 27-43), 12 weeks: time-restricted eating -0.94 kg vs consistent meal timing -0.68 kg; between-group difference -0.26 kg (95% CI -1.30 to 0.78, P = .63). Authors: 'not more effective in weight loss than eating throughout the day.'1. JAMA Internal Medicine
    Hemorrhoids and itchy anus (pruritus ani)Washing with water (bidet) instead of dry toilet paperMyth–––Systematic review: 'Two prospective trials and 1 cross-sectional study found that habitual use of bidets had no impact on the odds of developing hemorrhoids or hemorrhoidal symptoms.' Habitual bidet use 'may increase the odds of developing pruritus ani'; case series reported perianal burns. No meta-analysis possible.1. Evidence-Based Complementary and Alternative Medicine
    Childhood overweight and disordered eatingEating family meals together 3+ times a weekModerate–––Meta-analysis of 17 studies, 182,836 children and adolescents: sharing 3+ family meals a week was linked to 12% lower odds of overweight, 20% lower odds of eating unhealthy foods, 24% higher odds of eating healthy foods and 35% lower odds of disordered eating.1. Pediatrics
    Death from coronary heart diseaseTaking a midday nap (siesta)Weak––GreeceGreek EPIC, 23,681 adults without heart disease, 6.32 years: systematic nappers coronary mortality ratio 0.63 (95% CI 0.42-0.93); any siesta 0.66 (0.45-0.97). Meta-analysis of 11 cohorts (151,588 people): naps of 60+ min/day had CVD rate ratio 1.82 (1.22-2.71) and all-cause mortality 1.27 (1.11-1.45); naps under 60 min showed no link to CVD (P = 0.98).1. Archives of Internal Medicine
    2. Sleep
    Stroke and other cerebrovascular diseaseEating the last meal of the day before 8 pmWeak––FranceNutriNet-Santé, 103,389 French adults, median 7.2 years, 988 cerebrovascular cases: last meal after 9PM vs before 8PM HR 1.28 (95% CI 1.05-1.55). For overall CVD HR 1.13 (0.99-1.29) was not significant and for coronary disease 1.00 (0.83-1.20). In a Spanish weight-loss study of 420 people, late lunch eaters (after 15:00) lost less weight over 20 weeks (P = 0.002).1. Nature Communications
    2. International Journal of Obesity
    Death from any cause and from digestive diseaseDrinking several cups of coffee a dayModerate––Denmark, France, Germany, Greece, Italy, Netherlands, Norway, Spain, Sweden, United KingdomEPIC, 521,330 Europeans, 16.4 years, 41,693 deaths: highest vs non-drinkers, all-cause HR 0.88 (95% CI 0.82-0.95) in men and 0.93 (0.87-0.98) in women; digestive disease deaths HR 0.41 (0.32-0.54) men. Source: 'This relationship did not vary by country.' Women had higher ovarian cancer mortality, HR 1.31 (1.07-1.61). Umbrella review: 3-4 cups/day vs none, all-cause RR 0.83 (0.79-0.88).1. Annals of Internal Medicine
    2. BMJ
    Sick days taken from workEnding a daily shower with cold waterWeak––NetherlandsRandomized trial, 3,018 adults aged 18-65, Netherlands, 30 days of cold showers then 60 days optional: sickness absence incident rate ratio 0.71 (P = 0.003); 'For illness days there was no significant group effect.' A 2026 review of 13 studies (4,105 people) says evidence on cold-water exposure and mood is 'limited, heterogeneous, and at substantial risk of bias.'1. PLoS One
    2. Frontiers in Physiology
    Loss of independence in older age (functional disability)Soaking in a hot tub dailyWeak––JapanJAGES cohort, 13,786 older Japanese adults, 3 years, 1,203 disability cases: tub bathing 7+ times/week vs 0-2 times/week HR 0.72 (95% CI 0.60-0.85) in summer and 0.71 (0.60-0.84) in winter.1. Journal of Epidemiology