[email protected] wrote:
> >"A dietary lack of vitamin D may occasionally occur in people on a
> >vegetarian diet who do not drink milk products..."
>
> ...and don't spend much time outside in the sun... about 15 minutes
> will net you plenty.
>
> Patrick
http://www.westonaprice.org/nutrition_guidelines/nutrition_vitaminD.html
quote:
"The reason it is difficult to get adequate vitamin D from sunlight is
that while UV-A is present throughout the day, the amount of UV-B
present has to do with the angle of the sun's rays. Thus, UV-B is
present only during midday hours at higher latitudes, and only with
significant intensity in temperate or tropical latitudes. Only 5
percent of the UV-B light range goes through glass and it does not
penetrate clouds, smog or fog.
Sun exposure at higher latitudes before 10 am or after 2 pm will cause
burning from UV-A before it will supply adequate vitamin D from UV-B.
This finding may surprise you, as it did the researchers. It means that
sunning must occur between the hours we have been told to avoid. Only
sunning between 10 am and 2 pm during summer months (or winter months
in southern latitudes) for 20-120 minutes, depending on skin type and
color, will form adequate vitamin D before burning occurs.9
It takes about 24 hours for UV-B-stimulated vitamin D to show up as
maximum levels of vitamin D in the blood. Cholesterol-containing body
oils are critical to this absorption process.10 Because the body needs
30-60 minutes to absorb these vitamin-D-containing oils, it is best to
delay showering or bathing for one hour after exposure. The skin oils
in which vitamin D is produced can also be removed by chlorine in
swimming pools.
The current suggested exposure of hands, face and arms for 10-20
minutes, three times a week, provides only 200-400 IU of vitamin D each
time or an average of 100-200 IU per day during the summer months. In
order to achieve optimal levels of vitamin D, 85 percent of body
surface needs exposure to prime midday sun. (About 100-200 IU of
vitamin D is produced for each 5 percent of body surface exposed, we
want 4,000 iu.) Light skinned people need 10-20 minutes of exposure
while dark skinned people need 90-120 minutes.11
Latitude and altitude determine the intensity of UV light. UV-B is
stronger at higher altitudes. Latitudes higher than 30° (both north
and south) have insufficient UV-B sunlight two to six months of the
year, even at midday.12 Latitudes higher than 40° have insufficient
sunlight to achieve optimum levels of D during six to eight months of
the year. In much of the US, which is between 30° and 45° latitude,
six months or more during each year have insufficient UV-B sunlight to
produce optimal D levels. In far northern or southern locations,
latitudes 45° and higher, even summer sun is too weak to provide
optimum levels of vitamin D.13-15 A simple meter is available to
determine UV-B levels where you live."
end quote
TC
