A new study suggests that vitamin D may protect against prostate cancer (PCa), but some PCa specialists remain unconvinced.

The non-randomized trial was published online April 16 in The Journal of Clinical Endocrinology and Metabolism.  Fifty-two men with an average age of 65 years took 4,000 IU/day of vitamin D3 in soft-gel capsules. Forty-four of the subjects took it for a full year and had both safety and efficacy data available for analysis. Fifty-five percent of the men had a decrease in the number of positive cores or in Gleason score at repeat biopsy. No significant adverse events were observed.

The investigators compared with these patients with 19 control subjects with PCa who were similar to the test subjects but did not take vitamin D. Of these, 63% progressed compared with only 34% of vitamin D supplementation group. In addition, only 21% of control subjects had improved on repeat biopsy (experienced a decrease in the number of positive cores or no increase in Gleason score at repeat biopsy).

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“We are now performing a randomized study, which will take another two to three years to complete, but in the meantime our open-label study showed that the supplement seems to benefit subjects,” said lead investigator Sebastiano Gattoni-Celli, MD, Professor of Radiation Oncology at the Medical University of South Carolina in Charleston. “We are not claiming this is the end of the story, but it certainly is hopeful.”

However, Eric A. Klein, MD, Chairman, Glickman Urological and Kidney Institute, and Professor of Surgery at Cleveland Clinic Lerner College of Medicine, said the Selenium and Vitamin E Cancer Prevention Trial, which showed a significant increase in PCa incidence with vitamin E over the longer term, is a reminder of deleterious effects that can eventually be uncovered from “seemingly innocuous substances such as vitamins.”
He added that the lack of placebo control group in the new trial “makes the conclusion of this study tenuous.” In addition, “fewer positive cores after a year of supplementation is not evidence of disease stabilization, regression or lack of progression in biological aggressiveness,” Dr. Klein told Renal & Urology News. “Consumers should be wary of claims of benefits from dietary supplementation unless they are rigorously demonstrated in large-scale, placebo-controlled, randomized trials.”

Eric J. Jacobs, PhD, Strategic Director, Pharmacoepidemiology, National Home Office, American Cancer Society, Inc., Atlanta, agrees.

“Results of small studies such as this are interesting but preliminary. There is not adequate evidence for physicians to suggest to their prostate cancer patients that vitamin D supplements may be useful in treating their disease.”