The protective role of folate in preventing neural tube defects is now well established. The hypothesis is advanced here that photolysis of folate by ultraviolet (UV) light may, in some women, precipitate a folate deficiency sufficient to cause a neural tube defect (NTD) during the first few weeks of pregnancy. This hypothesis is supported by the demonstration of in vitro photolysis of folate by simulated strong sunlight, a decline in folate levels in light-skinned subjects exposed to UV light for dermatological conditions, and the occurrence of NTDs in the offspring of women who exposed themselves to high levels of UV light on the sunbeds of tanning salons. If established, a connection between in vivo folate photolysis by UV light, clinical folate deficiency and NTDs would suggest that intense or prolonged periconceptual exposure of women to UV light for recreational or therapeutic reasons should be avoided.
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