Whether you need more vitamin D is not simply a matter of how much is
pulsating through your body but rather which doctor you talk to. Confusion and doubt still linger in the medical community nearly two
years since the esteemed U.S. Institute of Medicine revised the recommendations
for daily vitamin D intake. It was in November 2010 when the IOM lowered the vitamin
D blood level deemed sufficient, from 30 nanograms/milliliter to 20 ng/ml. But
what this change has meant for the general population, most of whom don't even
know their vitamin D blood levels, has been a mystery … until now.
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| Researchers have calculated that 78.7 million adults once considered to have insufficient vitamin D levels now have sufficient levels under new guidelines issued by the Institute of Medicine. CREDIT: eurobanks | shutterstock |
Researchers at Loyola University Chicago Stritch School of Medicine have
done some number-crunching and have calculated that 78.7 million adults once
considered to have insufficient vitamin D levels now have sufficient levels under the new guidelines. Yet
many doctors and medical organizations, such as the Endocrine Society, still
abide by the old guidelines. This means a sizeable chunk of the U.S. adult
population — over one-third — is in "recommendation limbo."
A team led by Holly Kramer of Loyola published its calculation today
(Oct. 24) in the journal PLOS ONE.
D's source and purpose
Humans get most of their vitamin D from the sun. The sun's ultraviolet
radiation interacts with a type of steroid deep in the skin to make
cholecalciferol, colloquially known as vitamin D3. There are only a few food
sources rich in vitamin D, mostly fatty fish such as catfish and salmon. This
type of vitamin D is called ergocalciferol, or D2. Vitamin D is needed primarily for healthy bones. Low
levels can cause bone softening, a disease called rickets in children and osteomalacia in adults.
Some doctors think vitamin D improves the immune system and lowers the
risk of cardiovascular disease, cancer, multiple sclerosis and other ailments.
But the data supporting these claims are lacking, a fact reflected in the IOM's lowering
of the recommended vitamin D blood-level target.
Because most Americans do not eat much fatty fish, the sun remains the
primary source of vitamin D. However, many scientists say that, outside of the
warmer months, the sun's rays are too weak to generate enough vitamin D
anywhere north of 37 degrees latitude, an imaginary line stretching roughly
from Washington, D.C., and across St. Louis to San Francisco. Those with darker
skin will have a harder time making vitamin D. Air pollution and sunscreens
also reduce the amount of UV light hitting the skin. Hence, dietary supplements are recommended.
Talk to your doctor?
The Loyola-led study primarily examined the effect of the new vitamin D
recommendations on people with chronic kidney disease. Chronic kidney disease in adults is linked to low vitamin D
levels.
The study found that death rates from chronic kidney disease were
essentially the same for people with vitamin D levels anywhere in the range of
20 to 40 ng/ml and that only those patients with very low levels of vitamin D
had the highest risk of death.
So the IOM's lowering of the guidelines to 20 ng/ml hasn't worsened the
death rate from chronic kidney disease. But in calculating this, using data
from a large national health survey, the Loyola team could infer the number of
Americans with no chronic kidney disease and with a vitamin D level smack in
between 20 and 30 ng/ml. That's the 78.7 million. Kramer would not comment on what levels are best, stating only that
those people confused about the appropriate level should "consult with
their doctors." What your doctor might say is anyone's guess. "The
[Endocrine] Society's figure of 30 is still quite reasonable; indeed, even it
may not be high enough," said Robert Heaney, a professor at Creighton
University School of Medicine in Omaha, Neb., who was an author of the
Endocrine Society's clinical practice guideline on vitamin D. (Heaney added
that this is his opinion and that he's not authorized to speak on the behalf of
the society.)
Walter Willett, a respected nutritionist at Harvard School of Public
Health in Boston, also has said the IOM guidelines for vitamin D blood levels
are too low. In a comment co-written by Heike Bischoff-Ferrari of the
University of Zurich and published in Harvard's Nutrition Source newsletter
about the IOM recommendations, Willett cites two large studies from 2009 demonstrating
that the 20 ng/ml level is too low to prevent bone fractures from falls. Willett
and Bischoff-Ferrari added that, beyond bone health, "the evidence for
benefit is quite strong for some [disease prevention], especially colorectal
cancer," albeit not conclusive.
The IOM, part of the United States National Academies, is considered a
"who's who" of medical research, whose distinguished new members are
elected by current members. Willett, in fact, is a member. The IOM has not
ruled out revising its guidelines, particularly as stronger studies about
vitamin D's role beyond bone health come to light.
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