The idea is that too little of this critical vitamin in the body may cause cell growth to go awry, leading to cancer.

To test that idea, researchers checked vitamin D levels in 667 Chicago men between the ages of 40 and 79 who were having prostate biopsies because they'd recently had an abnormal prostate specific antigen (PSA) test or because a doctor felt changes to the prostate during a physical exam.

• Normal vitamin D levels are in the range of 30 to 80 nanograms per milliliter (ng/ml).
• Vitamin D deficiency, or a level under 20 ng/ml, was relatively common among all the men tested.
• About 44 percent of the men with positive biopsies and 38 percent of those who tested negative for cancer had low vitamin D levels.
• Among men who tested positive for cancer after their biopsies, those who also had very low levels of vitamin D under 12 ng/ml had greater odds of more advanced and aggressive cancers than those with normal levels.

The connection between vitamin D and cancer seemed to be even stronger in black men.

• Black men with vitamin D levels under 12 ng/ml were far more likely than those with normal levels to test positive for prostate cancer in the first place.
• In general, black men are also more likely to be diagnosed with prostate cancer. On average, men have about a one-in-seven lifetime risk of getting prostate cancer. That risk rises to one in five for black men, according to the U.S. Centers for Disease Control and Prevention.
• Researchers aren't sure whether lower vitamin D levels may help to explain why black men are at higher risk for prostate cancer. They say longer and larger studies are needed to sort out the connection.

A University of Colorado Cancer Center study published in the journal Prostate (2014) looked at the possibility that vitamin D may help reduce cancer-causing inflammation. Scientists found that the gene GDF-15, known to be up-regulated by vitamin D can help block a protein which stimulates tumor growth.

"When you take vitamin D and put it on prostate cancer cells, it inhibits their growth. But it hasn't been proven as an anti-cancer agent" said James Lambert, lead investigator at the University of Colorado Cancer Center. "We wanted to understand what genes vitamin D is turning on or off in prostate cancer to offer new targets."

Using a sophisticated computer algorithm, researchers analyzed samples of prostate cells and compared them to the prevalence of GDF-15 and inflammatory cells. Because they were able to demonstrate that vitamin D up-regulates the gene expression for GDF-15, they decided to further investigate to see if GDF-15 could be a pathway in which vitamin D inhibits prostate tumor growth. The results were compelling.

"There's been a lot of work on inhibiting NFkB," said Lambert. "Now, from this starting point of vitamin D in prostate cancer, we've come a long way toward understanding how we might use GDF-15 to target NFkB, which may have implications in cancer types far beyond prostate."