By Steven Reinberg
WEDNESDAY, March 2, 2016 (HealthDay News) -- Prostate cancer may be more aggressive in men who are deficient in vitamin D, new research suggests.
A study of nearly 200 men having their prostate removed found those with low vitamin D levels were more likely to have rapidly growing tumors than those with normal levels of the "sunshine" vitamin.
"If men with vitamin D deficiency are more likely to have [more advanced disease] at the time of prostate surgery, then perhaps men should be tested for this when they are diagnosed with prostate cancer and subsequently supplemented with vitamin D if they are deficient," said researcher Dr. Adam Murphy. He is an assistant professor of urology at Northwestern University in Chicago.
However, another expert isn't ready to go that far.
This study can't prove that vitamin D deficiency causes aggressive prostate cancer, only that the two are associated, said Dr. Anthony D'Amico, chief of radiation oncology at Brigham and Women's Hospital in Boston.
But D'Amico thinks the results are important enough to spur further study into the possible connection between vitamin D and prostate cancer. "It's a hypothesis that's worth testing," he said.
For now, though, D'Amico doesn't think enough evidence exists to recommend vitamin D supplements to prevent prostate cancer or make it less aggressive.
Murphy said he has been exploring the link between prostate cancer and vitamin D for some time. He said racial distinctions were noted in this study, too, with black men having more aggressive tumors and lower vitamin D levels than white men.
These findings suggest that one reason black men have higher odds of developing -- and dying of -- prostate cancer is because of their "higher propensity for having vitamin D deficiency from the sun-blocking effects of melanin and perhaps dietary intake differences," Murphy said. The study could not prove this, however.
The human body gets vitamin D from certain foods. These include fortified products (such as milk, orange juice and cereal), and certain fish (such as salmon), according to the U.S. National Institutes of Health. The body also makes the vitamin when the skin is exposed to sunlight. Dark-skinned people have more melanin, which prevents burning.
Murphy said men with dark skin, low vitamin D intake or low sun exposure should be tested for vitamin D deficiency when diagnosed with prostate cancer or elevated PSA (prostate specific antigen), which is associated with the cancer. He believes supplementation is warranted for those with low vitamin D levels.
The study included 190 men having prostate surgery. The researchers found that nearly 46 percent of the men had aggressive cancer, and these men had vitamin D levels about 16 percent lower than men with slower-growing tumors.
After accounting for age, PSA levels and abnormal rectal exams, Murphy and his colleagues found that vitamin D levels below 30 nanograms per milliliter (ng/mL) of blood were linked to higher odds of aggressive prostate cancer.
The report was published online recently in the Journal of Clinical Oncology.