Comment: Thank you much. Quite a lot of hard to find information.

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Thank you much. Quite a lot of hard to find information.

I believe in what you are finding. I have found & documented information related to what you offer here.

    "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."

Rather startling. For Boston, he makes an astonishing observation. I suspect if one went to a higher elevation, such as a mountain resort, on a clear day, a fair skinned Irishman... a redhead... could get a sunburn midday. I have here-to-fore believed that at the Sun's apex each sunny day, some UVB gets through the atmosphere to active the process of vitamin D3 production. Weather or dust does occlude UVB, no doubt. Perhaps the good doctor has makes a point we should all be made aware. We need vitamin D3.

Where may I find UVB measure by: location coordinate, time, & season. I see high/medium/low in local weather pages. More useful would be measures that would allow one to calculate when, where & how long. What sources do you recommend for D2 vs D3?

Disclaimer: Mark Twain (1835-1910-To be continued) is unlicensed. His river pilot's license went delinquent in 1862. Caution advised. Daily Paul