The majority of Americans up to age 70 are getting enough
vitamin D and calcium, according to a new Institute of Medicine (IOM) report.
The daily recommended intake (DRI) values are based on
findings from nearly 1,000 published studies as well as testimony from
scientists and stakeholders, which confirm the roles of calcium and vitamin D
in promoting skeletal growth and maintenance and the amounts needed to avoid
poor bone health.
The D factor
The dosage range for vitamin D is based on a review of
hundreds of studies and reports on other possible health effects, such as
protection against cancer, heart disease, autoimmune diseases and diabetes.
While these studies point to possibilities that warrant
further investigation, they have yielded conflicting and mixed results and do
not offer the evidence needed to confirm that vitamin D has these effects.
"There is abundant science to confidently state how much
vitamin D and calcium people need," says Catharine Ross, professor of
nutritional sciences at Penn State, who chaired the committee that issued the
report. "We scrutinized the evidence, looking for indications of beneficial
effects at all levels of intake. Amounts higher than those specified in this
report are not necessary to maintain bone health."
Daily Dosage
Most Americans up to age 70 need no more than 600
international units (IUs) of vitamin D per day to maintain health, and those 71
and older may need as much as 800 IUs, according to the Dietary Reference
Intakes (DRIs) report from the IOM.
The science on calcium's role in bone health shows that 700
milligrams per day meets the needs of almost all children ages
one-through-three and 1,000 milligrams daily is appropriate for almost all
children ages four-through-eight. Adolescents ages 9-through-18 require no more
than 1,300 milligrams per day.
For practically all adults ages 19-through-50 and for men
until age 71, 1,000 milligrams covers daily calcium needs. Women starting at
age 51 and both men and women age 71 and older need no more than 1,200
milligrams per day.
As for vitamin D, 600 IUs daily meets the needs of almost
everyone in the United States and Canada, although people 71 and older may
require as much as 800 IUs per day because of potential physical and behavioral
changes related to aging.
Some adolescent girls may not get quite enough calcium, and
there is a greater chance that elderly individuals may fall short of the
necessary amounts of calcium and vitamin D. These individuals should increase
their intake of foods containing these nutrients and possibly take a
supplement.
Dilemma about D
Confusion about the amount of vitamin D necessary to ward
off deficiency has arisen in recent years as tests that measure levels in
patients' blood have become widely used.
The measurements of sufficiency and deficiency -- the
cutpoints -- that clinical laboratories use to report test results have not
been based on rigorous scientific studies and are not standardized, meaning the
same individual could be declared deficient or sufficient depending on which
laboratory reads the test.
There may be an overestimation of the number of people with
vitamin D deficiency because many labs appear to be using cutpoints that are
higher than the evidence indicates are appropriate.
Although sunlight triggers the natural production of vitamin
D in skin and contributes to people's vitamin D levels, individuals' sun
exposure varies greatly and many people are told to minimize their exposure, so
the committee assumed minimal sun exposure to establish the DRIs. The new
intake levels for vitamin D cover the needs of individuals who get little sun.
Not too much
Greater amounts of food fortification and rising rates of
supplement use have increased the chances that people consume high amounts of
these nutrients. Getting too much calcium from dietary supplements has been
associated with kidney stones, for example, while excessive vitamin D can
damage the kidneys and heart.
"While it is too early to make definitive statements about the risks associated with routine high doses of vitamin D and calcium, people don't need more than the amounts established in this report," Ross says. "Past cases such as hormone replacement therapy and high doses of beta carotene remind us that some therapies that seemed to show promise for treating or preventing health problems ultimately did not work out and even caused harm. This is why it is appropriate to approach emerging evidence about an intervention cautiously, but with an open mind."
