Recent in vitro, animal, and human research has suggested a possible role for vitamin D in decreasing cancer incidence, mortality, or both. A new study that used data collected prospectively during the third National Health and Nutrition Examination Survey (NHANES) showed no association between levels of vitamin D in the blood and total cancer mortality, but did find a significant association between higher levels of circulating vitamin D and reduced risk of colorectal cancer mortality.

"Most of the previous studies on cancer mortality [and vitamin D] have been ecologic studies or have been based on surrogates for vitamin D levels. This is the first to look at actual measured levels and total cancer mortality," says Dr. Michal Freedman from NCI's Division of Cancer Epidemiology and Genetics, lead author of the study, which was published online October 30 in the Journal of the National Cancer Institute.

Between 1988 and 1994, the investigators from NCI and the Centers for Disease Control and Prevention collected data from 16,818 NHANES participants aged 17 or older, including demographic and lifestyle factors that may contribute to increased cancer risk. Each participant contributed a blood sample that was measured for vitamin D levels.

"We found no association between [vitamin D] and total cancer mortality in the…NHANES III study population," state the authors. However, participants with serum vitamin D levels at or above 80 nmol/L had a significantly lower risk of colorectal cancer mortality than participants with levels lower than 50 nmol/L.

The investigators cite several strengths of their study, including use of a study population that was derived from a representative sample of the U.S. population, and inclusion of many variables known to influence cancer risk. They also acknowledge limitations such as a low number of total cancer deaths to analyze and a single point of measurement for vitamin D, which may not represent blood levels over time.

"The relationship between nutritional factors and colorectal as well as other cancers is complicated…Randomized clinical trials of the effects of vitamin D on the incidence of colonic polyps and invasive cancer are needed," state Drs. Cindy Davis of NCI's Division of Cancer Prevention and Johanna Dwyer of the NIH Office of Dietary Supplements in an accompanying editorial.