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Vitamin D Levels
Dropping; Is Sun the Answer?
Vitamin D levels of the U.S.
population have dropped significantly over the past 20 years,
according to a recent study. Three-quarters of Americans now
show vitamin D levels below what many researchers consider necessary
for optimal health. Researchers disagree over how much help prudent
sun exposure may offer, but almost all agree that it can’t
be the whole answer.
The study showing drops in vitamin
D levels compared data from national health surveys conducted
from1988 to 1994 and 2001 to 2004. Vitamin D levels associated
with obvious deficiency increased from 2 percent to 6 percent
of the population from the earlier to later surveys. By the later
surveys, only 23 percent met the standard most researchers now
consider optimal for health – earlier reached by 45 percent
of the population. The greatest drops in vitamin D levels occurred
among African Americans; in the more recent surveys, 29 percent
showed vitamin D levels associated with deficiency and just 3
percent showed optimal levels. |
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Most people think of bone health
when they think of vitamin D. But this vitamin, which is technically
a hormone, seems to have impact beyond bones, including potential
to lower cancer risk. In at least some tissues, it seems to promote
normal cell development and "turn on" tumor suppressor
genes that inhibit uncontrolled cell growth characteristic of
cancer.
We have three potential sources
of vitamin D: diet, sunlight and supplements. Meeting current
U.S. guidelines through diet is challenging but possible. Wild
salmon three times a week would do it, but it’s not eco-friendly
to suggest we all try that. Three servings of vitamin D-fortified
milk, yogurt, juice or certain other fish plus minor amounts
from eggs, cheese and fortified cereal could do it for most of
us.
Current vitamin D recommendations
call for 200 International Unit (IU) daily from birth to age
50, 400 IU for ages 51 to 70, and 600 IU for age 71 and above.
The American Academy of Pediatrics now recommends that children
and teens should aim for 400 IU. However, these amounts are often
not enough to reach blood levels of vitamin D now seen as optimal.
Until updated recommendations are released in 2010, some experts
suggest aiming for 1000 to 2000 IU, which is identified as safe.
That’s a target diet alone can’t reach.
Much of our vitamin D is formed
in our skin following exposure to sunlight: Sunscreen sharply
decreases vitamin D production. Some researchers, such as Boston
University’s Michael Holick, suggest ten minutes of midday
sunlight on unprotected arms and legs two to three times per
week to improve vitamin D production. This is reportedly not
enough to cause skin damage that increases risk of skin cancer.
Others, including the American
Academy of Dermatology, disagree. They say that – especially
for people who live in the northern half of the country or have
dark skin, which reduces vitamin D production – sun exposure
cannot produce enough D to reach levels now considered protective.
They urge avoiding sun exposure without sunscreen to minimize
skin cancer risk and encourage food and supplements to provide
vitamin D.
While we wait for better agreement
about whether modest sun exposure is healthy or hazardous, researchers
agree than skin production of vitamin D is limited. At least
for light and medium pigmented skin, continued sun exposure beyond
a few minutes does not raise vitamin D levels but will increase
skin damage. And with or without sun exposure, more and more
seem to agree that vitamin D supplementation may be necessary
to reach optimal levels, at least until food fortification becomes
widespread. |
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