not, suggesting that a population getting more vitamin D would be healthier
overall. A recent Nebraska study links
increased vitamin D intake to less cancer risk, for example, while Japanese scientists find that the vitamin helps fight
influenza. Other recent work has connected higher levels of vitamin D with
lower risks of hypertension, Parkinson’s
disease and heart disease.
With these studies in hand, the
Endocrine Society put out its own recommendations in the July Journal of
Clinical Endocrinology & Metabolism.
The society, the world’s oldest and largest group devoted to hormone research,
called for vitamin D intake levels two to
three times higher than the IOM’s recommendations.
More randomized trials are needed to
settle the question, says Patsy Brannon,
a molecular nutritionist at Cornell University and a member of the IOM panel.
Until then, she says, it would be difficult
to justify raising the levels further. It
might even be imprudent because soaring levels could be toxic, she says.
That’s almost too much for nutritional
biochemist Bruce Hollis to bear. A longtime vitamin D researcher at the Medical
University of South Carolina in Charleston, Hollis recently oversaw a randomized
controlled trial showing that low blood
levels of vitamin D in pregnant women
may lead to more preterm births. He has
called for much higher doses. “These new
IOM levels won’t accomplish anything,”
Hollis says. “It’s just insane.”
Endocrinologist Robert Heaney of
Creighton University in Omaha, Neb.,
has spent a good part of his career compiling evidence that vitamin D has value
in bone health and beyond, particularly
in the fight against cancer. In a recent
study, his team randomly assigned 1,180
healthy postmenopausal women to
receive calcium, a placebo or 1,100 IU of
vitamin D plus calcium daily.
Over four years, the trial data showed
that those on the placebo had higher
cancer rates than the other groups, but
the findings revealed little difference
between those getting calcium alone
or calcium with vitamin D. Since cancer starts microscopically and can grow
undetected for months or years, the
researchers also ran an analysis that
skipped the first year — an effort to discount preexisting cancers. During the
last three years of the study, 6. 8 percent
of the placebo group and 3. 6 percent of
those getting only calcium developed
cancer, compared with 2.0 percent of
those getting vitamin D plus calcium,
Heaney’s team reported in 2007 in the
American Journal of Clinical Nutrition.
The Nebraska study is one of many
looking for a possible link between elevated cancer risk and low vitamin D in the
blood. Researchers have found a similar
association between vitamin D and colon
cancer and the formation of precancerous growths in the colon called polyps.
And Michael Holick, a biochemist and
endocrinologist at Boston University, can
reel off studies demonstrating less prostate and ovarian cancer in populations
with high sun exposure (meaning higher
vitamin D levels).
Holick, who chaired the commit-
tee that put out the Endocrine Society
guidelines, acknowledges a risk of skin
cancer from sun exposure in his 2010
book The Vitamin D Solution. But he and
others have estimated, based on rates
of cancer in the northern and south-
ern United States, that lives saved from
greater sun exposure would far exceed
those lost to skin cancer.
Using an entirely different bag of tricks,
vitamin D can stifle infections, a capability that was presaged nearly a century
ago when doctors successfully treated
Degrees of D people’s vitamin D blood levels differ because of various factors, including skin
color and sun exposure. Though scientists disagree on the level needed for good health, most peg
the value between 20 and 40 nanograms per milliliter. Data below come from specific populations.
Vitamin D blood levels around the world
men in Finland
Veiled Tunisian women,
age 20–60 (top)
Lifeguards in missouri
July 16, 2011 | SCIENCE NEWS | 23