Sunlight is a major source of vitamin D, since the skin naturally produces the nutrient after sun exposure. However, many people are now avoiding sun exposure (due to skin cancer risk), so their levels of vitamin D have dropped significantly. "It has placed the entire world population at risk for vitamin D deficiency," Holick said.
"We really need more research on health behaviors of cancer survivors," added Neli Ulrich, a molecular and nutritional epidemiology, folate, and pharmacogenetics researcher at the Fred Hutchinson Cancer Research Center in Seattle, and the author of an accompanying journal editorial.
Whether vitamin D actually prolongs patient survival isn't clear, Ulrich said. "It's an association at this point. We cannot tell for sure until it has been replicated and eventually a randomized trial has been done," she said.
Ulrich noted that the while many cancer patients take vitamin supplements, whether they are of benefit or are harmful isn't yet known. "We know that vitamin D has some toxicity," she noted.
For more on vitamin D and cancer, visit the American Cancer Society.
SOURCES: Kimmie Ng, M.D., M.P.H., Dana-Farber Cancer Institute, Boston; Michael F. Holick, M.D., professor, department of medicine, Endocrine Laboratory, Boston University; Neli Ulrich, Ph.D., molecular and nutritional epidemiology, folate, pharmacogenetics research, Fred Hutchinson Cancer Research Center, Seattle; June 20, 2008, Journal of Clinical Oncology
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