Vitamin D may be linked to aggressive prostate cancer

NEW YORK (Reuters Health) - Contrary to findings from some earlier studies, new research suggests that elevated vitamin D levels do not decrease the risk of prostate cancer and may, in fact, increase the risk of aggressive disease, although the researchers emphasize that none of the associations were statistically significant.

In laboratory studies, there has been evidence that high doses of vitamin D may cut the risk of the malignancy, but in epidemiologic studies, the results have been inconsistent. Few studies, however, have looked at whether disease aggressiveness may influence the associations, according to the report in the June 4the issue of the Journal of the National Cancer Institute.

In the current investigation, a nested case-control study of over 749 men with prostate cancer and 781 matched controls without cancer, increased serum levels of vitamin D raised the risk of aggressive (Gleason score of 7 or higher or clinical stage III or IV) prostate cancer by up to 96%. However, the overall risk of prostate cancer was not influenced by the vitamin D level.

For men with vitamin D levels in the lowest quintile, the rate of aggressive disease was 406 per 100,000 person-years, while those with levels in the other quintile had rates of up to 780 per 100,000 person-years, Dr. Jiyoung Ahn and colleagues from the Prostate, Lung, Colorectal, and Ovarian

Cancer Screening Trial Project Team report.

Still, the associations were not linear and did not reach statistical significance. For instance, the odds ratios for aggressive disease relative to vitamin D levels in the lowest quintile (number 1) were 1.20, 1.96, 1.61, and 1.37 for quintiles number 2, 3, 4, and 5, respectively. Thus, patients with moderate levels had the highest risk of aggressive disease. 

Nonetheless, Dr. Ahn, from the National Cancer Institute in Bethesda, Maryland, and colleagues found that the associations were consistent in patient subgroups based on age, family history of prostate cancer, diabetes, body mass index, calcium and other factors.

According to a related editorial, the present null findings require confirmation and "even if ultimately confirmed, should not be misinterpreted as evidence against other well-documented health benefits of vitamin D," Drs. Lorelei A. Mucci and Donna Spiegelman, from Brigham and Women's Hospital and Harvard Medical School in Boston write.

"The weight of evidence does suggest that increased vitamin D levels -- from diet, supplementation, or sun exposure -- are likely to have a modest beneficial effect on the overall burden of chronic disease in the United States and other epidemiologically similar countries."