“Dastardly”
A search for standards
The United States and Canadian
governments commissioned
the Food and Nutrition Board
of the Institute of Medicine
(IOM), the organization that
establishes appropriate dietary
intake values for vitamins and
minerals, to formally review
studies on vitamin D and calcium and develop new recommendations. The IOM report
was released in November,
2010—but it has not settled
matters. It is considered by some
to be too conservative and has
been the source of significant
controversy and debate.
Vitamin D basics
There are several sources for
vitamin D. A unique source is
sun exposure, which allows the
body to make its own vitamin
D. This is why vitamin D is
often referred to as the “sunshine
vitamin.” Vitamin D may also
be consumed in
foods and dietary
supplements.
However, only a
few foods, most
notably oily fish
(such as salmon),
naturally contain
significant amounts
of vitamin D. In
the United States, a
limited number of
other foods, including dairy products,
cereals and orange
juice, are fortified
with vitamin D.
Vitamin D levels in the body
are measured with a blood test,
which reports on blood levels
as “nanograms per milliliter” or
“ng/ml.” Many clinical laboratories and publications define
“sufficient” levels as 30–100 ng/
ml, “insufficient” levels as 20–30
ng/ml and levels below 20 ng/ml
as “deficient.” Some have argued
that the lower range of “
sufficient” should be 40, not 30 ng/
ml. But the recent IOM report
proposes that the lower range of
“sufficient” should be 20 ng/ml.
The IOM report also recommends an increase in intake, also
known as the Recommended
Daily Amount, or RDA, for
vitamin D. The RDA is the
daily intake that is thought to
meet or exceed the requirements
for 97.5% of the population.
The newly developed RDA for
vitamin D for adults is 600–800
international units (IU). The
adult RDA for calcium is now
Some professional organizations, physicians and scientists
don’t agree. They propose that
the RDA for vitamin D should
be significantly higher than
600–800 mg, based on the
results of studies in a variety of
conditions.
Vitamin D deficiency
The prevalence of vitamin D
deficiency may be difficult
to determine precisely. Since
vitamin D is synthesized in
the body by sunlight exposure,
vitamin D levels naturally vary
with geographic location and
time of year. And, as noted,
there is controversy about what
levels of vitamin D are consid-
ered deficient. The IOM report,
using lower levels for deficiency,
analyzing intake, and averag-
ing results from many stud-
ies, concluded that vitamin D
deficiency is not common in
the United States or Canada.
However, other studies in the
United States and Europe have
concluded that 40–100% of
elderly people are vitamin D
deficient. One study of Ameri-
can adults who had a reasonable
intake of vitamin D found that
about one-third of them were
vitamin D deficient as measured
by their blood levels.
Biological effects of vitamin D
For years it has been known that
vitamin D regulates calcium
absorption and thus maintains
bone health. Recent studies have
