Annual mean daily solar radiation
Female breast cancer mortality rates by state
Rates per 100,000
person-years, 1970–2004
On the map Scientists who study vitamin D can’t help but notice that a host of diseases seem to vary with latitude. Type 1 diabetes, multiple
sclerosis and even some cancers appear to be more common in areas that get less sun — meaning less opportunity for the body to produce vitamin D. The maps above illustrate the apparent link between solar radiation and breast cancer mortality rates.
SourcE, FroM lEFT: D.M. harriS anD v.l.w. go/J. OF NUTRITION 2004; na Tional cancEr inS Ti Tu TE
500 or more 450–500 400–450 350–400 300–350 300 or less More than 33.66 32.08–33.66 30.08–32.08 29.44–30.08 28.80– 29.44 27.96–28.80 26.93–27.96 less than 26.93 cal/cm2
D is for discord
The IOM panel members acknowledged
all of these findings — and didn’t use any
of them in setting vitamin D recommendations. They were very forthcoming
about why.
“ We looked extensively at those areas,”
Brannon says. In non-bone research, she
says, “we found very limited randomized
controlled trials, and evidence for cause
and effect was not present.”
Some studies did get special note.
Hollis’ trial in pregnant women is inter-
esting but had yet to appear in a peer-
reviewed journal, Brannon says, so it
wasn’t used in setting the recommen-
dations. The Nebraska cancer study was
discounted because the most convincing
Aging brain Studies have shown a link
between vitamin D blood levels and some
age-related disorders. The chart below shows
that parkinson’s patients more often have
lower levels than healthy controls.
Vitamin D insufficiency in Parkinson’s
patients versus healthy controls
Percent with vitamin D
30 nanograms per milliliter or less
60
50
55%
40
36%
30
20
10
0
Parkinson’s
patients
Healthy
controls
finding used only three of the four
trial years, says panel member JoAnn
Manson, an endocrinologist and epidemiologist at Harvard Medical School.
She says the full scope of a trial is the
only fair measure and that secondary
analyses lack credence.
Two large randomized controlled trials are now getting under way and will
provide new evidence.
Physician Carlos Camargo of Harvard
Medical School and colleagues at the University of Auckland are randomly assigning 5,100 older adults in New Zealand to
get a monthly pill containing either a placebo or 100,000 IU of vitamin D — equal
to about 3,300 IU a day. The trial will
assess heart disease, infections and fractures. “It’s a high enough dose to get most
participants up to 35 to 40 nanograms per
milliliter, which is where we think we’ll
find optimum benefits,” Camargo says.
Manson is leading a U.S. trial in
which 20,000 people age 60 and older
are being randomly assigned to get
2,000 IU a day or a placebo. Some will
also get omega- 3 fatty acids. Since they
don’t know what they are getting, participants are allowed to take vitamin D
supplements up to 800 IU daily on their
own. Researchers will measure heart
disease, cancer and stroke among the
participants.
Manson says she hopes the trial “will
provide important information about
the balance of benefits and risks” of
vitamin D.
Whatever the results, though, these
two trials may not settle the question.
A randomized trial is only as good as its
design, Cannell says. Giving people huge
doses of vitamin D once a month cre-
ates unnatural swings in the body. “Our
ancestors didn’t get one day of sun then
29 days without it,” he says.
Explore more
s M.F. holick et al. “Evaluation, treatment and prevention of vitamin D
deficiency: an Endocrine Society
clinical practice guideline.” Journal of
Clinical Endocrinology & Metabolism.
July 2011.
E. FEliciano
www.sciencenews.org
