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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 skin cancer and premature aging.
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 achieve an adequate
blood level of vitamin D.
During summer months, particularly in the southern
latitudes, some individuals acquire enough
sun exposure to maintain adequate vitamin D
levels. 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 the
risk of skin cancer, 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
could 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: “Vitamin D from
food and dietary supplements offers the same
benefits — without the danger of UV exposure —
as vitamin D obtained from the sun1.”
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 people should get. At present, the National Institutes of Health2
maintains that, unlike other vitamins, there is
insufficient scientific information to establish
a Recommended Dietary Allowance (RDA) for
vitamin D. However, they list Adequate
Intake (AI) amounts as follows: 200 IU
from birth to age 50, 400 IU for ages 51-70, and
600 IU beyond age 70. Check periodically on the NIH's website2 because they
might soon adjust their recommendation. Based on
recent research, many experts now believe that the
average healthy adult should ingest a total of 800 to
1,000 IU daily to maintain an adequate level of vitamin D.
In June, 2007, the Canadian Cancer Society3
recommended that adults who do not get much sun
should take a daily 1,000 IU vitamin D
supplement.
More studies are needed to determine the optimum
intake, particularly for children. A 2003
report by the American Academy of Pediatrics4
recommends a daily supplement of 200 IU for
"children and adolescents who do not
get regular sunlight exposure, do not
ingest at least 500 mL per day of
vitamin D-fortified milk, or do not
take a daily multivitamin supplement
containing at least 200 IU of
vitamin D."
Vitamin D supplements are most effective if
taken with food. But,
Beware! Vitamin D can be toxic in high doses. The NIH lists 2,000 IU per day as
the upper limit
for safety.
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. Until more
evidence is available, a total daily
intake in the range of 800 to 1,000 IU is reasonable for healthy
sun-safe adults.
We eagerly await further
research results that might help to
ascertain a recommended daily allowance of
vitamin D for children. There is no evidence that 400 IU daily would be
harmful to normal healthy school-age children, and
supplementation seems
prudent for children who practice careful sun
protection or who have dark skin pigmentation. However,
to avoid toxicity do not exceed the upper limit
of 2,000 IU per day. Parents are encouraged
to ask their pediatrician for specific advice
pertaining to their child.
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1
http://www.aad.org/ (type “vitamin D” into
the search site dialog box)
2
http://ods.od.nih.gov/factsheets/vitamind.asp
3
http://www.cancer.ca/ccs/internet/mediareleaselist/
0,3208,3172_1613121606_1997621989_langId-en,00.html
4
http://aappolicy.aappublications.org/
cgi/content/full/pediatrics;111/4/908
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