some U.K. teens, sun doesn’t provide enough vitamin D
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[June 01, 2016]
By Kathryn Doyle
(Reuters Health) - At one point in the
year, almost 80 percent of teens in a UK study had insufficient vitamin
D that should come from sun exposure, and one quarter had insufficient
levels even at the peak of summer, according to a new study.
The results were surprising because the participants were white
children, whose skin is the most sensitive to ultraviolet-B and who
therefore need the least amount of sunlight exposure to get enough
vitamin D, said senior author Lesley E. Rhodes of the University of
Manchester in the U.K.
Most vitamin D is synthesized in the skin after exposure to UVB rays
from the sun, Rhodes and colleagues write in the Journal of Clinical
Endocrinology and Metabolism. Little comes from foods, they point
out, and the UK doesn’t recommend a specific dietary intake of
In January, April, June and September 2011, the researchers
collected blood samples from 131 Caucasian adolescents ages 12 to
They tested for the main circulating form of vitamin D in the blood,
For one week of each season, the participants wore UV radiation
dosimeters and also kept sun exposure diaries of every 15-minute
period spent outdoors, with weather conditions, clothing and
sunscreen use. They also recorded intake of vitamin D supplements,
vitamin D-fortified foods, and oily fish, butter, margarine, milk,
eggs, cheese and red meat.
The teens tended to get more sun exposure during the school week
than on weekends, and they had low levels of vitamin D intake in
their diets year-round. None reported wearing dedicated sunscreen
products in any season, though a few female teens were using
SPF-containing face cream.
On average, 25OHD levels were 24.1 nanograms per milliliter (ng/mL)
in September at their peak and 15.5 ng/mL in January, their lowest
point. Those with less than 10 ng/mL circulating 25OHD were
considered vitamin D “deficient” and those with less than 20 ng/mL
Sixteen percent of kids were deficient in vitamin D in at least one
season. Those individuals had X-ray imaging of their lumbar spines
and femoral necks to estimate bone mineral density, and only one
appeared to have abnormally low bone mineral density.
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Adolescence is a key stage for laying down bone mass, so deficiency
in teen years may result in suboptimal bone health, Rhodes said in
A white skinned person at UK latitudes needs less than 15 minutes of
midday unshaded summer sunlight daily to get enough vitamin D, which
is not enough time to cause sunburn, she said.
“Short exposures to sunlight that do not make the skin pink or red
later (i.e. cause sunburn) help maximize the benefits of sunlight
while minimizing the risks,” she said. “People who stay longer in
the sun and cause their skin to redden have over-exposed and
increase their risk of skin cancer later on.”
Kids may need to be tested more often for vitamin D levels, but
further research and guidance from national authorities should come
first, Rhodes said.
SOURCE: http://bit.ly/1UfpNNq Journal of Clinical Endocrinology and
Metabolism, online May 26, 2016.
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