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Vitamin D
The one health benefit that sunlight has on
human skin is the production of vitamin D.
Unfortunately, the ultraviolet rays that stimulate vitamin D
production (UVB rays) are the same ones that
cause sunburn and skin cancer.
There isn't very much vitamin D in the
typical American's diet. Some is
present in oily fish (e.g., salmon, mackerel,
sardines) milk, and fortified cereal or orange
juice, but dietary sources alone are usually not
sufficient for a healthy blood level without the
addition of substantial sun exposure or a
vitamin supplement.
Vitamin D deficiency can cause rickets in
children, and osteoporosis in adults. An
increased risk of other ills, such as cancer of
the colon, breast, or prostate, as well as
multiple sclerosis and type 1 diabetes might be
linked to vitamin D deficiency. More
research is needed before all of these
associations can be considered certain but in
the meantime it seems reasonable for everyone to
take prudent measures to maintain an adequate
blood level of vitamin D.
During summer months, particularly in the southern
latitudes, some individuals acquire enough
sun exposure to achieve an adequate vitamin D
level. However, while sun exposure is an
effective source of vitamin D, it can
simultaneously increase the risk of skin cancer.
When sunscreen is applied to the
skin, it not only reduces sun damage, but unfortunately it also blocks vitamin
D production.
Darkly pigmented skin, advanced age, and low UV index
(e.g., winter months in northern latitudes) are
some of the factors that decrease the amount of
vitamin D produced by the skin in response to
sun exposure. Because of the dual impact
of the sun's UV rays (skin cancer induction and
vitamin D production) those with the lightest
skin pigment are at the highest risk of
sun damage resulting in skin cancer, while people
with darker skin pigment are at lower risk of
skin cancer but higher risk for
vitamin D deficiency.
Some
authorities recommend routine limited or
"sensible" sun
exposure for vitamin D. However, too many variables affect the amount of
exposure time needed (e.g., season, time of day,
weather conditions, skin color, age) making it
impossible to give a simple recommendation such
as
"[X] minutes of sun per day" that
would be assured to provide sufficient vitamin D
for all people. This introduces the risk that
people will unintentionally over-expose (fall
asleep while sunning) and increase their risk of
skin cancer in the process. Sun Safety for Kids agrees with the
American Academy of Dermatology which
"does not recommend getting vitamin D from sun
exposure (natural) or indoor tanning
(artificial) because ultraviolet (UV) radiation
from the sun and tanning beds can lead to the
development of skin cancer1.”
The amount of Vitamin D in food or
in a supplement is commonly listed in International
Units (IU). Evidence is still emerging to
determine the ideal safe and effective amount of
vitamin D that average healthy people should
ingest. At present, the National Institutes of Health2
recommends an intake of 600 IU per day for
Americans 1 to 70 years of age. Some
experts recommend a higher intake, in the range
of 1,000 - 2,000 IU/day but the NIH warns that
intakes in excess of 4,000 IU/day might lead to
vitamin D toxicity. The NIH also
discourages intentional sun exposure as a source
of vitamin D, saying "it is prudent to limit
exposure of skin to sunlight."
Because vitamin D is fat soluble, vitamin D
supplements are most effective if taken with
food.
The directors of Sun Safety for Kids believe
that optimum health will be achieved if people
practice careful sun protection year round and
compensate by ingesting a sufficient daily
amount of vitamin D.
Blood Test
A simple blood test called "25-hydroxy
vitamin D" measures circulating vitamin D and
provides a fair assessment of the body's vitamin
D status. The NIH recommends that the level
should be 21 ng/ml or higher, but some experts suggest that blood levels in the
range of 30 to 50 ng/ml are preferred. There is
no evidence that levels above 50 provide any
added benefit and vitamin D toxicity becomes a
concern with higher levels. Levels
tend to fluctuate with the seasons (lower in
winter/higher in summer) due to incidental sun
exposure. A doctor might order the blood test
to help in determining the
amount of vitamin D supplementation that will
provide optimum vitamin D status year round.
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1
http://www.aad.org/media-resources/stats-and-facts/prevention-and-care/vitamin-d/vitamin-d
2
http://ods.od.nih.gov/factsheets/VitaminD-QuickFacts/
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