Night light alters menstrual cycles

Abstract

Dewan asserted 20 years ago that a bedside light could shorten and regularize the menstrual cycle among women with long and irregular menstrual patterns. To replicate this, seven volunteers slept with a 100-watt bulb by the bedside from days 13–17 of their menstrual cycles, while nine controls similarly used a dim red placebo (photographic safe light). Indeed, the 100-watt bulbs shortened menstrual cycles from a mean of 45.7 days to 33.1 days and reduced variability, but the placebo had no effect. These results suggest that light may have promise for treatment of infertility, for contraception, and for other endocrine interventions.