Spectral Character of Sunlight Modulates Photosynthesis of Previtamin D 3 and Its Photoisomers in Human Skin

The photosynthesis of previtamin D 3 from 7-dehydrocholesterol in human skin was determined after exposure to narrow-band radiation or simulated solar radiation. The optimum wavelengths for the production of previtamin D 3 were determined to be between 295 and 300 nanometers. When human skin was exposed to 295-nanometer radiation, up to 65 percent of the original 7-dehydrocholesterol content was converted to previtamin D 3 . In comparison, when adjacent skin was exposed to simulated solar radiation, the maximum formation of previtamin D 3 was about 20 percent. Major differences in the formation of lumisterol 3 and tachysterol 3 from previtamin D 3 were also observed. It is concluded that the spectral character of natural sunlight has a profound effect on the photochemistry of 7-dehydrocholesterol in human skin.