Vitamin D recommendations
Although calcium gets most of the publicity, vitamin D is equally
important in preventing bone loss and fractures. Without it, our bodies
can't properly absorb and utilize the calcium we take in. Vitamin D
also helps maintain normal blood levels of phosphorus, another bone-building
mineral. Vitamin D would be essential if it did nothing else, but researchers
have discovered that it's active in many tissues besides bone and may
play a role in warding off a range of diseases, including cancer, hypertension,
Physicians have known for years that vitamin D deficiencies often occur
in people with liver and kidney disease, because these organs are involved
in making the active form of vitamin D. Because our bodies make vitamin
D when exposed to the sun, elderly and housebound people with poor diets
are also known to be at risk. But recent studies suggest that the problem
isn't confined to these groups, and that many adults have inadequate
levels of vitamin D in their blood, especially in northern latitudes
where long winters keep people indoors more. The shortfall may lead to
fractures, osteoporosis, and other chronic conditions. Moreover, the
incidence of nutritional rickets — a severe vitamin D-deficiency
disease once thought to have been nearly eliminated — is on the
rise in North America. And researchers at Boston 's Children's Hospital
recently reported that 24% of Boston-area adolescents, especially African
Americans, are vitamin D deficient.
As a result, some experts are beginning to question the adequacy of
current recommendations for vitamin D. They're also speculating that
the campaign to protect our skin from the sun has had a harmful effect
on our ability to get enough of the sunshine vitamin.
How much more do we need?
The vitamin D recommendation was revised upward in 1997, to 400 IU/day
for adults ages 51–70 and 600 IU/day for those over 70. These revised
levels reflected a new understanding of vitamin D's role in preventing
osteoporosis. But many experts believe the new recommendations are still
inadequate for preventing osteoporosis and other conditions associated
with low vitamin D.
Some experts believe that adults should take 800–1,000 IU daily
of supplemental vitamin D to adequately prevent bone loss and possibly
protect against some cancers and other chronic disorders. Another possibility
might be to take a single weekly dose of 5,000 IU or a single 100,000-IU
dose every few months. In a randomized trial in the United Kingdom ,
the latter strategy helped reduce fracture rates in elderly women and
men. Subjects taking a single 100,000 IU vitamin D capsule every four
months for five years had a rate of first fracture that was 22% lower
than those taking a placebo, and they had a 33% lower fracture rate at
the hip, wrist, and vertebrae.
What does this mean?
Given the limitations of sun exposure and dietary vitamin D, the best strategy
may be to simply take a vitamin D supplement. Until we know more about
the optimal level for bone health, it may make sense to increase your daily
intake to 800 IU, especially in northern latitudes. (Be sure you also get
1,000–1,200 mg/day of calcium.) The government has set the safe upper
limit at 2,000 IU/day. You can't overdose on the vitamin D your skin makes,
and it's unlikely you'll eat enough of it in food to get you into trouble.
February 2004 Update
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