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Just curious: why isn't the making of vitamin D by the human skin called photosynthesis?

Photosynthesis is predominantly powered by red and blue visible light. The manufacture of Vitamin D in our skin is triggered by UV. Also in humans Vitamin D is not an energy source, unlike the sugars commonly produced by photosynthesis in plants.

Thanks. This article is also clear about the differences: http://en.wikipedia.org/wiki/Photochemistry

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