The effect of gender on the melatonin suppression by light : a dose response relationship

It is well known that light is an inhibitor of pineal melatonin secretion in humans. However, the effect of gender on the melatonin suppression by dim and bright light is still controversial. The present study investigated the effect of gender on the suppression of melatonin at five light intensities (0, 200, 500, 1,000, 3,000 lux). Five healthy men and women attended five testing sessions separated by one week. At each session, subjects were exposed to light from midnight to 0100 hours in a sitting position. Blood samples where collected at regular intervals and plasma melatonin concentration was measured using a specific radioimmunoassay. No gender differences were found in melatonin suppression by light at any of the five light intensities (p > 0.1). Furthermore, the mean melatonin suppression by light in both males and females was dose dependent (17% [200 lux], 40% [500 lux], 56% [1,000 lux] and 74% [3,000 lux]). Our findings suggest that melatonin suppression by light in intensity dependent, with no gender differences in light sensitivity.