Educational only. Not medical advice.
Sun Exposure and Winter UV Levels
Epidemiological research published in the Annals of the New York Academy of Sciences (1999; 889:107–119) observed that regions with limited winter sunlight—whether due to latitude, cloud cover, or air pollution—tend to report higher rates of certain cancers, particularly colon cancer. In the United States, mortality from colon cancer has historically been higher in the Northeast than in the South.
These geographic patterns mirror older maps of rickets, a condition caused by vitamin D deficiency. In northern states, winter sunlight is often too weak for the skin to produce vitamin D for several months each year. Researchers have suggested that these sunlight patterns may help explain differences in disease rates across regions.
Similar associations have been noted for breast cancer mortality in white women and for multiple sclerosis, both of which tend to be more common at higher latitudes where winter UV exposure is reduced.
Vitamin D and Calcium Intake
The same report also highlighted findings that colon cancer rates appear inversely related to calcium intake. Observational data and laboratory models suggest that vitamin D and calcium play roles in supporting normal cell growth and immune function. Some analyses propose that regular intake of approximately 1,800 mg of calcium and 800 IU (20 mcg) of vitamin D3 may be associated with lower rates of colon cancer in adults.
For women, an estimated 1,000 mg of calcium per 1,000 calories consumed, along with 800 IU/day of vitamin D3, has been proposed as a supportive intake level in some studies.
While these findings do not prove cause and effect, they highlight nutritional and environmental patterns that may influence long-term health outcomes.
The Bigger Picture
Geography, climate, diet, and sunlight exposure all appear to play a role in various health trends. Understanding how factors such as vitamin D status, seasonal UV levels, and calcium intake intersect may help explain why certain conditions—including colon cancer, breast cancer mortality patterns, and MS—tend to cluster in regions with less sun exposure.
