Those with vitamin D levels above a certain threshold had a 70 percent greater risk of developing one of these cancers. (That threshold was 15 nanograms per milliliter; people with less than that were considered deficient in vitamin D.)
People with higher vitamin D levels also tended to develop their skin cancer on parts of the body not typically exposed to sunlight, like the arms and legs, but that finding was not statistically significant, the researchers reported.
At this research stage, it's difficult to untangle the possible mechanisms behind this.
"It's a triangular relationship between UV light with the production of Vitamin D and the induction of skin cancer," Eide said. "That makes it difficult to know."
The study didn't take into account lifetime sun exposure, family history of skin cancer, vitamin D supplementation, exercise, smoking or several other factors that might have influenced the outcome of the study. In addition, the study authors noted that it was "highly likely" that the participants' exposure to sunlight might have skewed the results.
"We need some measure of lifetime cumulative UV exposure, which is very difficult to measure," Eide said. "We tend to move around a lot; people go on vacations. There could be critical windows during our life."
The Skin Cancer Foundation has more on all forms of skin cancer.
SOURCES: Melody J. Eide, M.D., staff physician/scientist and dermatologist, Henry Ford Hospital, Detroit; Vijay Trisal, M.D., assistant professor of surgical oncology, City of Hope Cancer Center, Duarte, Calif.; Aug. 15, 2011, Archives of Dermatology
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