Sunshine, if it is high in the sky during the spring and summer and fall between the hours of 10 AM and 2 PM can produce, I am told, in a fair skinned person, about 20,000 IUs in 20 minutes of sunbathing. The skin produces it from cholesterol when exposed to UVB light. A dark skinned person needs more time in the sun to produce as much. Once the blood levels of vitamin D get too high, the skin will start to destroy it. So you cannot overdose on vitamin D from sunshine.
The key is not how much you take, but how high your blood levels are.
I posted links to talks and articles about it below.
Dr. Holick says in his lecture you can run around naked in the sun during the Boston winter, but you will not produce vitamin D. The UVB rays are filtered out by the atmosphere when the sun is too low in the sky.
I was taking 15,000 IUs per day and had a blood test a year ago last December. My vitamin D level was 49ng/ml. That is the low end of optimal.
East and West doesn't matter for sunshine. The farther one is away from the equator, the harder it is to get the sun high enough in the sky. Typically, the sun will do its job in the continental U.S. from about April to September. From October to March, either use a UVB sun lamp or supplement.
[F]orce can only settle questions of power, not of right. - Clyde N. Wilson
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