Low blood levels of vitamin D may be linked to more aggressive and advanced cases of prostate cancer in men, a new study suggests.
And black men with low vitamin D levels were more
likely than those with normal levels to test positive for cancer after a
prostate biopsy.
The study, published May 1 in the journal Clinical Cancer Research,
suggests that vitamin D may play an important role in how prostate
cancer starts and spreads, although it does not prove a cause-and-effect
relationship. Researchers aren't yet sure exactly how it comes into
play or even if taking extra vitamin D might keep prostate cancer in
check.
"There are still many questions about this
relationship that have to be answered," said Dr. Len Lichtenfeld, deputy
chief medical officer at the American Cancer Society. He was not
involved in the research.
"We really don't know, for certain, what role
vitamin D plays in cancer -- either the genesis or beginning of cancer
-- or in defining how aggressive the cancer may be," he said. "Further
research has to be done."
What is known is that vitamin D plays several critical roles in how cells develop and grow.
"It seems to regulate normal differentiation of
cells as they change from stem cells to adult cells. And it regulates
the growth rate of normal cells and cancer cells," said study author Dr.
Adam Murphy, an assistant professor of urology at Northwestern
University's Feinberg School of Medicine, in Chicago.
Vitamin D is also known as the "sunshine vitamin"
because skin makes it when exposed to sunlight. Vitamin D levels tend to
drop with advancing age, and deficiency is more common in seasons and
regions that get less sunlight and in people with darker skin, which
naturally blocks the sun.
What about the vitamin's possible relationship to cancer?
"When you squirt vitamin D on prostate cells in a petri dish, their rate of growth slows down," Murphy said.
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.
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