May 27 (HealthDay News) -- Men with a high blood concentration of vitamin D don't have a reduced risk of prostate cancer, National Cancer Institute researchers report.

Previous laboratory studies had suggested that high doses of vitamin D may decrease prostate cancer risk, but epidemiological studies of that association have yielded mixed results.

In this new study, researchers compared blood concentrations of vitamin D of 749 prostate cancer patients and 781 men without the disease. The blood samples were collected at the start of the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial, and all the prostate cancer cases included in this study were diagnosed one to eight years after collection of the blood samples.

Increased vitamin D concentrations weren't associated with a statistically significant difference in prostate cancer risk. While there was some evidence of a link between higher concentrations of vitamin D and increased risk of aggressive prostate cancer, the trend wasn't statistically significant, and the association didn't show a linear dose-dependence.

The study was published in the May 27 online issue of the Journal of the National Cancer Institute.

"Results from this large prospective study of men who underwent standardized prostate cancer screening in the context of a screening trial do not support the hypothesis that higher serum vitamin D status is associated with decreased risk of prostate cancer," the study authors wrote.

"The study showed no association of vitamin D with non-aggressive disease; however, it raises the possibility that higher vitamin D level may be associated with increased risks for aggressive disease, although a clear monotonic dose-response relationship is lacking, " the researchers noted.

Last year, a National Cancer Institute team published a long-term study that said high blood levels of vitamin D don't reduce overall cancer death risk, but may offer some protection against colorectal cancer.

SOURCE: Journal of the National Cancer Institute, news release, May 27, 2008