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Counting on the
sun alone for vitamin D will leave most people deprived of
adequate amounts of this nutrient, especially during the winter
in the northern parts of the US.
This is true even
for people who work outside during the summer and get plenty
of sun in the warmer months but not in the winter.
Vitamin D is formed
in the skin, but it requires ultraviolet rays of the sun to
activate it to a form the body can use. Vitamin D, which assists
the intestines in absorbing calcium and phosphorus, is also
contained in some fortified foods.
Dr. Robert Heaney
from Creighton University calculated the daily skin dose of
vitamin D that 26 men who worked outdoors during the summer
would have received.
They brought the
men back about 6 months later to assess how much vitamin D
they may have lost over the winter. The team estimated that
the amount of vitamin D that the group had received from the
sun during the summer was equivalent to approximately 2800
international units (IU) of vitamin D a day.
Current RDAs of
vitamin D are 200 IU per day for adults aged 19 to 50, 400
IU for those aged 51 to 70, and 600 IU for those over 70.
When the men were
reassessed during February and March of the following year
For the purposes of this study, vitamin D insufficiency was
defined as a serum 25 OH D concentration of <15 n/ml. Over
one-third had serum 25 OH vitamin D concentrations of less
than 15 ng/ml, while the mean total 25 OH D concentration
was 19.4 ng/ml.
The researchers
concluded that vitamin D deficiency is more common than previously
thought and it is not restricted to high-risk groups such
as the homebound elderly.
24th
Annual Meeting of the American Society for Bone and Mineral
Research San Antonio, Texas September 24, 2002
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