Vitamin D production from skin UV exposure is self-regulated. UV irradiation converts 7-DHC to pre-D3, but continued exposure to UV-B converts pre-D3 to lumist

Vitamin D production from skin UV exposure is self-regulated. UV irradiation converts 7-DHC to pre-D3, but continued exposure to UV-B converts pre-D3 to lumisterol and tachysterol. As pre-D3 levels fall, lumisterol and tachysterol can be converted back into pre-D3 or shed with dead skin. Pre-D3 is slowly converted to D3 with heat exposure.