Vitamin d from sun exposure
Vitamin D from Sun Exposure?
April 27, 2014

A study following 29,518 Swedish women shows that
those who avoided sun exposure were twice as
likely to die over 20 years compared to those who
spent significant time in sunlight (J Intern Med,
published online April 4, 2014). This does not
mean that lack of sunlight causes death; it means
only that lack of sunlight is associated with
increased rate of death in this study. It could
mean only that people who are sick do not spend as
much time in the sunlight.
 
You Need Sunlight or Pills to Meet Your Needs of
Vitamin D
 To meet your needs for vitamin D, you must expose
your skin to sunlight or take vitamin D pills.
Even though vitamin D-fortified dairy products,
eggs and liver contain vitamin D, most foods are
severely deficient in that vitamin and you are
highly unlikely to meet your needs from your diet
alone. Excessive exposure to sunlight can cause
skin cancers, so it would be helpful to know the
least amount of time that you have to expose your
skin to sunlight to meet your daily needs for
vitamin D.
 
Researchers have estimated the minimal amount of
sun exposure necessary to have your skin make
enough vitamin D to equal the same blood level of
vitamin D3 that you would get from taking 400 or
1000 IU vitamin D for people living in Miami FL,
and Boston MA, during the months of January,
April, July, and October (J Am Acad Dermatol,
June, 2010;62(6):929). You get the highest
concentration of ultraviolet B rays, which are
necessary for the skin to synthesize vitamin D, at
high noon:
 * Boston: From April to October at 12 Noon EST,
an individual with light skin, with 25 percent of
the body surface area exposed, needs to spend 3 to
8 minutes in the sun daily to synthesize 400 IU of
vitamin D. It is difficult to get enough sunlight
to synthesize vitamin D during the winter in
Boston.
 * Miami: An individual with light skin, with 25
percent of the body exposed, would need to spend 3
to 6 minutes at 12 Noon EST to synthesize 400 IU.
Vitamin D synthesis occurs faster in individuals
with lighter skin.
 
Sun Causes the Most Skin Damage at High Noon
 You do not want to expose your skin to sunlight
at high noon because that is the time at which the
sun causes the most skin damage per the amount of
vitamin D the skin makes. In a study from
Australia, researchers calculated the amount of
sun exposure needed to have your skin make enough
vitamin D to equal the same blood level of vitamin
D that you would get from taking 200-600 IU of
vitamin D pills per day for people aged 19-50
years with fair skin exposing 15 percent of the
body (Med J Aust, 2006 Apr 3;184(7):338-41).
Australia and Florida are located roughly the same
distance from the equator. In January (mid-summer
in Australia), 2-14 minutes of sun three to four
times per week at 12:00 Noon was sufficient to
ensure recommended vitamin D production. However,
the skin can turn red, a sign of sun damage, in as
little as eight minutes.
 
At 10:00 AM and 3:00 PM, your skin can make far
more vitamin D and receive far less damage and
redness than from noon sun exposure. This is the
recommended time to expose your skin to reduce the
risk for sun burn and skin cancer. October to
March, about 10-15 minutes of sun exposure at
around 10:00 AM or 3:00 PM three to four times per
week should be enough for fair-skinned people
across Australia to produce recommended vitamin D
levels. Longer exposure times are needed from
April to September, particularly in southern
regions of Australia.
 
My Recommendations
 If you have very dark skin, it will be very
difficult for you to meet your needs for vitamin D
through sunlight exposure in most cities in North
America. On the other hand, if your skin is fairly
light, you probably can meet your needs for
vitamin D all year round in Florida and in the
summertime in most North American cities. Get a
blood test for hydroxy vitamin D in January or
February. If it is above 50 nmol/L (20 ng/mL), you
are normal and do not need supplementation. If it
is below that, you may need to take vitamin D
pills during the winter.

(See also:
Muslce soreness exercise injury and vitamin D
Take vitamin d pills only if you have a deficiency)