I'm wondering: from a Vitamin-D production point of view, is it the same to :
It depends. Are we talking near the equator? Or New York in January? At some point, the body maxes out on how much D3 can be synthesized, so if you were hitting the limit, then spreading out your exposure to the sun would be helpful. But if you aren't at the limit, it won't matter whether it's one 10-minute session or 10 1-minute sessions.
This PDF -- "Environmental factors that influence the cutaneous production of vitamin D" -- has some useful info. Or you can also check out the Norwegian Institute for Air Research's UV calculator for a specific recommendation for exposure.
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