Vitamin D from Sunlight Linked to Reduced Risk of The Most Lethal Forms of Cancer

A new study suggests that lack of exposure to ultraviolet B radiation from the sun may increase the risk of developing four types of cancer. The study found that Americans living in places that receive the most sunlight have higher mortality from skin cancer but significantly lower mortality from breast and ovarian cancer, prostate cancer and colon cancer.

Researchers examined cancer mortality rates in the U.S. between 1970-1994 and compared those rates with ultraviolet-B radiation levels in certain areas in the U.S. The researchers discovered that more deaths from skin cancer occurred in the sunnier areas, but death from other cancers was significantly lower in those same sunny locales. The findings of the study confirmed that solar UV-B radiation is associated with reduced risk of cancer of the breast, colon, ovary, prostate and non-Hodgkin lymphoma. In addition, cancers of the bladder, esophagus, kidney, lung, pancreas, rectum, stomach, and corpus uteri were linked to low levels of UV-B radiation from the sun. The researchers suggested that annually, in white Americans, 21,700 premature deaths from cancers could be prevented by exposure to UV-B radiation or supplementation with vitamin D3, 1400 deaths could be prevented in African Americans, and 500 deaths could be prevented in Asian Americans and other minorities.

The reason sunlight may offer protection, researchers believe, is because sunlight triggers a reaction in the body that manufactures vitamin D. Studies have linked low circulating levels of vitamin D due to lack of sunlight exposure or low levels of dietary vitamin D with increased risk of colorectal, prostate and breast cancers. According to the study author, in the northern United States, sunlight levels are so low that in winter vitamin D synthesis is inadequate to produce protective levels of this important vitamin.

The results of the current study, wrote lead researcher Dr. Grant, demonstrate that much of the geographic variation in cancer mortality rates in the U.S. can be attributed to variations in solar UV-B radiation exposure. Thus, many lives could be extended through increased careful exposure to solar UV-B radiation and more safely, vitamin D3 supplementation, especially in nonsummer months.

These results did not entirely surprise the researchers as past studies have documented that sunlight may protect against breast, ovarian, prostate, and colon cancer and that cancer rates from these types of malignancies are approximately twice as high in the northeast compared with the sunny southwest. Researchers believe that risk factors such as diet fail to explain this increased cancer incidence.

Reference:
Grant WB. An estimate of premature cancer mortality in the U.S. due to inadequate doses of solar ultraviolet-B radiation. Cancer. 2002 Mar 15;94(6):1867-75.