Vitamin D May Promote Colon Cancer Survival

However, Ng believes that most people are probably not getting enough vitamin D anyway. "Patients should talk with their physician about whether vitamin D supplementation would be good for their health overall," Ng said.

Despite these and other findings, experts continue to debate the role of vitamin D in cancer treatment and prevention.

Dr. Michael F. Holick, a professor in the department of medicine's Endocrine Laboratory at Boston University, is convinced that high doses of vitamin D can reduce the risk of malignancy and aid in cancer treatment.

"This finding is outstanding," Holick said. "It is consistent with dozens and dozens of observations that have been made in the past decade," he said.

Holick believes that most people do not get enough vitamin D. "Vitamin D deficiency is the most common medical condition worldwide," he said. "Everyone, children and adults, should be on at least 1,000 International Units (IU) of vitamin D a day."

That level is far above current recommendations, Holick said. "Everybody now agrees that those recommendations need to be markedly increased," he said.

The recommended daily doses of vitamin D supplements range from 200 IU a day for those under 50 to 400 IU for those 50 to 70 and 600 IU for people over 70.

For clinical trials to really determine whether vitamin D is effective as a cancer preventative or treatment, the dose of vitamin D needs to be very high, Holick said.

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.

More information

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