Search by category for epidemiological vitamin D studies:

Latitude, Vitamin D, and Disease Rate Studies

Seasonal Vitamin D Level Changes

Winter Sickness Rate Studies

Air Pollution and Population Vitamin D Levels


Global Breast Cancer Seasonality (2010)

Conclusion: 2,921,714 breast cancer cases from 64 different global regions were analyzed. There is a consistent, world-wide increase in breast cancer diagnoses in the spring and fall. This increase is even stronger in regions farther away from the equator. Fall is when most people’s vitamin D levels begin dropping as the solar radiation starts to get weaker going into winter. Spring is when most people’s vitamin D levels are at their lowest, as they are coming out of winter and this is when it’s most difficult, or completely impossible, for many people to produce their own vitamin D from sun exposure.


The Association Between Ultraviolet B Irradiance, Vitamin D Status and Incidence Rates of Type 1 Diabetes in 51 regions Worldwide (2008)

Conclusion: Incidence rates of Type-1 diabetes are generally higher at latitudes farther away from the equator where there is less UVB radiation necessary for vitamin D production in humans. Type-1 diabetes incidences decrease in regions closer to the equator.


Could Ultraviolet B Irradiance and Vitamin D be Associated With Lower Incidence Rates of Lung Cancer? (2008)

Conclusion: Lung cancer incidence rates were investigated in 111 different countries. Lung cancer rates were found to be higher in latitudes farther from the equator and in areas with higher cloud cover. These would also be areas of the world that receive less solar UVB radiation, which is necessary for vitamin D production.


Seasonal and Geographical Variations in Lung Cancer Prognosis in Norway. Does Vitamin D from the Sun Play a Role? (2007)

Conclusion: An investigation of lung cancer incidence rates in Norway found that patients diagnosed in autumn have a lower fatality rate than those diagnosed in winter – winter being when most people’s vitamin D levels drop.


Vitamin D Status and Glucose Homeostasis in the 1958 British Birth Cohort: The Role of Obesity (2006)

Conclusion: Vitamin D levels and BMI were measured in 7,198 adult caucasian subjects in the 45-year British birth cohort survey. The vitamin D levels of the obese subjects were found to be lower than the non-obese subjects.


Solar ultraviolet-B exposure and cancer incidence and mortality in the United States, 1993-2002 (2006)

Conclusion: For the period of 1993 to 2002, satellite-measured solar UV-B levels, 3+ million cancer incidences, and 3 million cancer deaths in America were analyzed. There was a correlation between lower UVB levels and an increased rate of  “bladder, colon, Hodgkin lymphoma, myeloma, prostate, rectum, stomach, uterus, and vulva” cancer, and to a lesser extent for “breast, kidney, leukemia, non-Hodgkin lymphoma, pancreas, and small intestine” cancer.


Serum 25-hydroxyvitamin D concentrations in girls aged 4–8 y living in the southeastern United States (2006)

Conclusion: This study of 168 young girls living in the southeastern U.S. found that those with lower vitamin D levels had a lower bone mineral content, white girls have higher vitamin D levels than black girls (due to the increased melanin preventing vitamin D synthesis), their vitamin D levels dropped in the winter, and their levels increased in the summer. These girls also were found to have higher vitamin D levels compared to girls living at higher latitudes. Despite the black girls having lower pre-vitamin D levels, they had a higher bone density than the white girls. This adds support to findings of people of darker-skinned races possibly have differing vitamin D endocrine systems.


Epidemiology of Community-Acquired Pneumonia in Edmonton, Alberta: An Emergency Department-Based Study (2005)

Conclusion: In Edmonton, Alberta, winter brings a significant increase in the rate of community-acquired pneumonia cases. Winter is when people’s vitamin D levels tend to start dropping.


Timing of Birth and Risk of Multiple Sclerosis: Population Based Study (2005)

Conclusion: People with multiple sclerosis are more commonly born after winter, when population vitamin D levels are typically at their lowest.


Do Sunlight and Vitamin D Reduce the Likelihood of Colon Cancer? (2005)

Conclusion: This epidemiological study found that between 1959 and 1961, the American states that received the most average daily solar radiation (southern latitude states) had the lowest mortality rates for colon cancer and the northern latitude states had significantly higher colon cancer mortality rates.


The Prevalence of Hypovitaminosis D Among US Adults: Data from the NHANES III (2005)

Conclusion: This study of the vitamin D levels of 15,390 American adults found that the men had higher vitamin D levels than the women, white people have higher vitamin D levels than hispanics and blacks (due to increased melanin blocking the UVB necessary for vitamin D synthesis), and although white males had the best vitamin D levels, 34% still tested low. The study also found that elderly people have lower levels compared to younger adults (as we age we slowly lose our ability to cutaneously synthesize vitamin D).


Influenza and Pneumonia Hospitalizations in Ontario: A Time-Series Analysis (2004)

Conclusion: In Ontario, the influenza and pneumonia case rates significantly increase during winter and significantly decrease during summer. These rates correlate with the seasonality of people’s vitamin D levels.


Incidence of Juvenile-Onset Crohn’s Disease in Scotland: Association with Northern Latitude and Affluence (2004)

Conclusion: Children in Northern Scotland have been found to have higher incidences of Crohn’s disease compared to children in Southern Scotland.


Ecologic Analysis of Some Immune-Related Disorders, Including Type 1 Diabetes, In Australia: Latitude, Regional Ultraviolet Radiation, and Disease Prevalence (2003)

Conclusion: A positive correlation has been found between type 1 diabetes rates and latitude in Australia.


A Systematic Review and Meta-Analysis of Northern Hemisphere Season of Birth Studies in Schizophrenia (2003)

Conclusion: Schizophrenics tend to be born more in winter and spring compared to other seasons, when vitamin D-creating UVB radiation is less available. They also tend to be born more in latitudes farther away from the equator, which get less UVB radiation.


Epidemiology and Seasonality of Respiratory Tract Virus Infections in the Tropics (2003)

Conclusion: For tropical regions (in Asia, Africa, and South America), there has been an observed increase in respiratory viral infections during the rainy seasons.


Seasonal Fluctuations in Hospitalisation for Pneumonia in Finland (2001)

Conclusion: Finland experiences an increase in pneumonia cases during winter time, when people’s vitamin D levels tend to start dropping.


Geographic Variation of MS Incidence in Two Prospective Studies of US Women (1999)

Conclusion: There are more incidences of multiple sclerosis in the northern regions of the United States that the southern regions, which are closer to the equator and enjoy more vitamin D-creating UVB solar radiation.


Seasonal Variation in Hospital Admissions for Community-Acquired Pneumonia: A 5-Year Study (1999)

Conclusion: Community-acquired pneumonia rates increase in the winter and spring, when most people’s vitamin D levels decrease.


Prevalence of Vitamin D Insufficiency in an Adult Normal Population (1997)

Conclusion: This study analyzed the vitamin D levels of 1,569 adults in 20 different French cities. The northern populations had a much higher rate of vitamin D-deficiency than the southern populations.


Seasonal Variation in Vitamin D (1994)

Conclusion: People’s vitamin D levels tend to peak around the end of summer and significantly decrease throughout winter.


Seasonality of Hip Fracture and Haemorrhagic Diseases of the Newborn (1993)

Conclusion: Hip fracture rates for newborns reach their peak January-February and occur least July-August. These rates are in correlation with seasonal vitamin D level changes. Adequate vitamin D is essential for bone health.


Geographic Patterns of Prostate Cancer Mortality. Evidence for a Protective Effect of Ultraviolet Radiation (1992)

Conclusion: There are lower prostate cancer mortality rates in the southern regions of America compared to the northern regions due to the south receiving stronger sunlight with more vitamin D-producing UVB radiation.


Geographic Variation in Breast Cancer Mortality in the United States: A Hypothesis Involving Exposure to Solar Radiation (1990)

Conclusion: The U.S. breast cancer mortality rate is lower in the South and Southwest regions of America (which are closer to the equator and get more UVB) than it is in the Northeast (farther away from the equator, less UVB).


Sunlight and Breast Cancer Incidence in the USSR (1990)

Conclusion: “ The pattern of increased breast cancer incidence in regions of low solar radiation in the USSR is consistent with the geographical pattern seen for breast cancer mortality in the US and worldwide.”


Effect of Vitamin D Intake on Seasonal Variations in Parathyroid Hormone Secretion in Postmenopausal Women (1989)

Conclusion: The parathyroid hormone levels of postmenopausal women peak following the end of winter and hit their lowest levels following the conclusion of summer. This strongly correlates with documented seasonal changes in population vitamin D levels.


Influence of Season and Latitude on the Cutaneous Synthesis of Vitamin D3: Exposure to Winter Sunlight in Boston and Edmonton Will Not Promote Vitamin D3 Synthesis in Human Skin (1988)

Conclusion: Due to the unavailability of UVB solar radiation in the high northern latitudes during winter, it is impossible for humans to synthesize their own vitamin D between November and February in Boston and between October and March in Edmonton, Alberta.


The Role of Season in the Epidemiology of Influenza (1981)

Conclusion: Influenza tends to occur more in the winter time.


Epidemiology of the Hong Kong-68 Variant of Influenza A2 in Britain (1971)

Conclusion: Britain experiences increased influenza rates during winter time.


Also see 

Vitamin D Randomized Control Trials


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