Vitamin D Helps
Build Bone But Evidence Lacking That It Lowers Risk of Other Disease
IOM sets new dietary
intake levels for calcium and vitamin D: Aging senior citizens,
especially women, need more than others
Nov.
30, 2010 – In an effort to clarify the hype for increased consumption of
vitamin D that has developed in recent years, the Institute of Medicine
has issued a new report concluding
the evidence supports a role for these nutrients in bone health but not
in preventing other diseases. The committee found that the majority of
Americans and Canadians are receiving adequate amounts of both calcium
and vitamin D, and warns there is emerging evidence that too much may be
harmful.
Most Americans
and Canadians up to age 70 need no more than 600 international units (IUs)
of vitamin D per day to maintain health, and those senior citizens 71
and older may need as much as 800 IUs, says the IOM report. It also says
there is no proof that Vitamin D provides protection against cancer,
heart disease, autoimmune diseases, or diabetes.
Review of 28 studies finds the vitamin associated
with a substantial decrease in cardiovascular disease, type 2 diabetes
and metabolic syndrome for seniors and middle aged
The amount of
calcium needed ranges, based on age, from 700 to 1,300 milligrams per
day, according to the report, which updates the nutritional reference
values known as Dietary Reference Intakes (DRIs) for these interrelated
nutrients.
The report's
recommendations take into account nearly 1,000 published studies as well
as testimony from scientists and stakeholders. A large amount of
evidence, which formed the basis of the new intake values, confirms the
roles of calcium and vitamin D in promoting skeletal growth and
maintenance and the amounts needed to avoid poor bone health.
More Study
Needed on Protection from Other Diseases
The committee
that wrote the report also reviewed hundreds of studies and reports on
other possible health effects of vitamin D, 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.
Rigorous trials
that yield consistent results are vital for reaching conclusions, as
past experiences have shown. Vitamin E, for example, was believed to
protect against heart disease before further studies disproved it.
"There is
abundant science to confidently state how much vitamin D and calcium
people need," said committee chair Catharine Ross, professor and Dorothy
Foehr Huck Chair, department of nutritional sciences, Pennsylvania State
University, University Park.
"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."
IOM and Dietary Reference Intakes for Calcium and Vitamin D
Calcium and vitamin D are
two essential nutrients long known for their role in bone
health. Over the last ten years, the public has heard
conflicting messages about other benefits of these
nutrients—especially vitamin D—and also about how much calcium
and vitamin D they need to be healthy.
To help clarify this issue,
the U. S. and Canadian governments asked the Institute of
Medicine (IOM) to assess the current data on health outcomes
associated with calcium and vitamin D. The IOM tasked a
committee of experts with reviewing the evidence, as well as
updating the nutrient reference values, known as Dietary
Reference Intakes (DRIs).
These values are used
widely by government agencies, for example, in setting standards
for school meals or specifying the nutrition label on foods.
Over time, they have come to be used by health professionals to
counsel individuals about dietary intake.
The committee provided an
exhaustive review of studies on potential health outcomes and
found that the evidence supported a role for these nutrients in
bone health but not in other health conditions. Overall, the
committee concludes that the majority of Americans and Canadians
are receiving adequate amounts of both calcium and vitamin D.
Further, there is emerging evidence that too much of these
nutrients may be harmful.
How Much
Calcium Needed
The science on
calcium's role in bone health shows that 700 milligrams per day meets
the needs of almost all children ages 1 through 3, and 1,000 milligrams
daily is appropriate for almost all children ages 4 through 8.
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 elderly
men and women age 71 and older need no more than 1,200 milligrams per
day.
(See chart below
news story for new adult requirements of calcium and vitamin D)
How
Much Vitamin D Needed Daily
As for vitamin
D, 600 IUs daily meets the needs of almost everyone in the United States
and Canada, although seniors 71 and older may require as much as 800 IUs
per day because of potential physical and behavioral changes related to
aging.
The majority of
Americans and Canadians are getting enough vitamin D and calcium, the
committee determined from reviewing national surveys of blood levels.
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.
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.
This lack of
agreement means 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.
Based on available data, almost all
individuals get sufficient vitamin D when their blood levels are at or
above 20 nanograms per milliliter as it is measured in America, or 50
nanomoles per liter as measured in Canada.
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.
Risks of Too
Much Vitamin D or Calcium
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,
while excessive vitamin D can damage the kidneys and heart.
Evidence about
other possible risks associated with routine vitamin D supplementation
is still tentative, and most studies have focused on very high doses
taken short term rather than on routine, long-term consumption of large
amounts. However, some signals suggest there are greater risks of death
and chronic disease associated with long-term high vitamin D intake,
which informed the committee's conclusions about levels that consumers
should not exceed.
Vitamins and Minerals: About Vitamin D
Vitamins are organic
substances (made by plants or animals), minerals are inorganic
elements that come from the earth; soil and water and are
absorbed by plants. Animals and humans absorb minerals from the
plants they eat. Vitamins and minerals are nutrients that your
body needs to grow and develop normally.
Vitamins and minerals have a
unique role to play in maintaining your health. For example
Vitamin D helps your body absorb the amount of calcium (a
mineral) it needs to form strong bones. A deficiency in vitamin
D can result in a disease called rickets (softening of the bones
caused by the bodies inability to absorb the mineral calcium.)
The body cannot produce calcium; therefore, it must be absorbed
through our food.
Other minerals like
chromium, copper, iodine, iron, selenium, and zinc are called
trace minerals because you only need very small amounts of them
each day. The best way to get enough vitamins is to eat a
balanced diet with a variety of foods. You can usually get all
your vitamins from the foods you eat.
About Vitamin D
Vitamin D is a fat-soluble
vitamin that is naturally present in very few foods, added to
others, and available as a dietary supplement. It is also
produced endogenously when ultraviolet rays from sunlight strike
the skin and trigger vitamin D synthesis. Vitamin D obtained
from sun exposure, food, and supplements is biologically inert
and must undergo two hydroxylations in the body for activation.
The first occurs in the
liver and converts vitamin D to 25-hydroxyvitamin D [25(OH)D],
also known as calcidiol. The second occurs primarily in the
kidney and forms the physiologically active
1,25-dihydroxyvitamin D [1,25(OH)2D], also known as calcitriol.
Vitamin D is essential for
promoting calcium absorption in the gut and maintaining adequate
serum calcium and phosphate concentrations to enable normal
mineralization of bone and prevent hypocalcemic tetany.
It is also needed for bone
growth and bone remodeling by osteoblasts and osteoclasts.
Without sufficient vitamin D, bones can become thin, brittle, or
misshapen. Vitamin D sufficiency prevents rickets in children
and osteomalacia in adults.
Together with calcium,
vitamin D also helps protect older adults from osteoporosis.
Vitamin D has other roles in
human health, including modulation of neuromuscular and immune
function and reduction of inflammation. Many genes encoding
proteins that regulate cell proliferation, differentiation, and
apoptosis are modulated in part by vitamin D. Many
laboratory-cultured human cells have vitamin D receptors and
some convert 25(OH)D to 1,25(OH)2D. It remains to be determined
whether cells with vitamin D receptors in the intact human carry
out this conversion.
Upper intake
levels represent the upper safe boundary and should not be misunderstood
as amounts people need or should strive to consume. The upper intake
levels for vitamin D are 2,500 IUs per day for children ages 1 through
3; 3,000 IUs daily for children 4 through 8 years old; and 4,000 IUs
daily for all others.
The upper intake
levels for calcium are 2,500 milligrams per day from age 1 through 8;
3,000 milligrams daily from age 9 through 18; 2,500 milligrams daily
from age 19 through 50; and 2,000 milligrams per day for all other age
groups.
"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 said.
"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."
The new DRIs are
based on much more information and higher-quality study results than
were available when the DRIs for these nutrients were first set in
1997. At that time, limitations in the evidence resulted in intake
levels called Adequate Intakes, which are rougher estimations of
people's requirements than the new values. The old and new DRIs reflect
different calculations and are not directly comparable.
The study was
sponsored by the U.S. Department of Health and Human Services, U.S.
Department of Agriculture, U.S. Department of Defense, and Health
Canada. Established in 1970 under the charter of the National Academy
of Sciences, the Institute of Medicine provides independent, objective,
evidence-based advice to policymakers, health professionals, the private
sector, and the public. The National Academy of Sciences, National
Academy of Engineering, Institute of Medicine, and National Research
Council make up the National Academies. For more information, visit
http://national-academies.org.
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Nov.
30, 2010 – In an effort to clarify the hype for increased consumption of
vitamin D that has developed in recent years, the Institute of Medicine
has issued a new report concluding
