Effects of UVA irradiation on the concentration of folate in human blood.

Although it is well known that ultraviolet A (UVA) irradiation destroys folate, no definite conclusion for the biological degradation has yet been drawn. In the present study, we determined the effects of UVA exposure on the blood folate concentration in vitro and in vivo. UVA irradiation reduced the synthesized folate pteroylmonoglutamic acid (PGA) content in the blood, but not 5-methyltetrahydrofolate, a major folate form in the blood stream. Exposure to sunlight also decreased the plasma folate concentration in human subjects who took PGA prior to the exposure, but not in subjects who did not take PGA. These results suggest that UVA exposure destroyed PGA but not 5-methyltetrahydrofolate in human blood in vivo.