THURSDAY, June 19 (HealthDay News) -- Colon cancer patients with high blood levels of vitamin D boost their survival odds by 48 percent, a new study suggests.

Previous studies have indicated that high levels of vitamin D may reduce the risk of getting colon cancer by 51 percent, although other studies dispute that claim. But until now, no studies have looked at whether vitamin D could improve survival among people who already had the disease.

"Vitamin D has been studied for many years, and there is a lot of data that it could be implicated in cancer pathogenesis," explained lead researcher Dr. Kimmie Ng, from the Dana-Farber Cancer Institute in Boston. "Vitamin D is involved a lot of things that can go wrong in cancer," she noted.

According to Ng, the vitamin may improve survival in colon cancer patients by slowing the growth of tumor cells. It may also be involved in killing cancer cells and inhibiting the growth of blood vessels in tumors.

The report is published in the June 20 edition of the Journal of Clinical Oncology.

In the study, Ng's team collected data on 304 patients diagnosed with colon cancer between 1991 and 2002. These patients participated in either the Nurses Health Study or the Health Professionals Follow-Up Study.

All those in the study had their vitamin D levels measured at least two years before being diagnosed with colon cancer.

The patients' health was tracked until they died, or until 2005, whichever came first. During the follow-up period, 123 patients died, 96 of them from colon or rectal cancer, the researchers report.

The team found that patients with the highest levels of vitamin D were 48 percent less likely to die from colon cancer or any other cause, compared with those with the lowest levels.

For colon cancer alone, those with the highest vitamin D levels were 39 percent less likely to die, compared with those with the lowest levels of vitamin D, Ng's group found.

Ng doesn't yet advocate vitamin D supplements as a means of preventing or treating cancer, however. "Definitive evidence that our results are due to vitamin D would require a randomized clinical trial," Ng said.

Clinical trials are planned to determine if adding vitamin D to chemotherapy after surgery improves colon cancer survival, the researcher said.

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.