According to the results of a study published in the American Journal of Epidemiology, sun exposure may reduce the risk of advanced breast cancer among women with light skin pigmentation.

Vitamin D is a fat-soluble vitamin that comes from dietary supplements, foods such as fortified milk and cereal, certain kinds of fish (including salmon, mackerel, and tuna), and exposure to sunlight. Vitamin D is hypothesized to play a role in the prevention of some types of cancer.

To explore the relationship between sun exposure-a source of vitamin D-and risk of breast cancer, researchers conducted a study among a multiethnic group of women in California. The study enrolled 1,788 women with breast cancer and 2,129 women without breast cancer.

Skin pigmentation was assessed at the underside of the upper arm-an area generally not exposed to sun. A sun exposure index was developed by comparing this area of the skin to the skin of the forehead-an area of the skin that often does receive sun exposure. Study participants were also asked about their lifetime history of outdoor activity.

• Lifetime outdoor activity was not linked with breast cancer risk in any of the three skin pigmentation groups (light, medium, dark).
• Among women with light skin pigmentation, those with the highest sun exposure index (based on comparison of skin on the forehead to skin on the underside of the upper arm) were roughly half as likely to develop advanced breast cancer as those with the lowest sun exposure index.
• Among women with medium or dark skin pigmentation, there was no significant relationship between sun exposure index and risk of advanced breast cancer.
• There was no significant relationship between the sun exposure index and risk of localized breast cancer in any of the skin pigmentation groups.

The researchers conclude that sun exposure may decrease the risk of advanced breast cancer among women with light skin pigmentation. They note that these findings “add to the growing body of evidence that vitamin D plays a role in the natural history of breast cancer.”

Because sun exposure increases the risk of skin cancer, the potential benefits of sun exposure are likely to be accompanied by risks.

Reference: John EM, Schwartz GG, Koo J, Wang W, Ingles SA. Sun exposure, vitamin D receptor gene polymorphisms, and breast cancer risk in a multiethnic population. American Journal of Epidemiology. 2007;166:1409-1419.

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