The effect of age and pre-light melatonin concentration on the melatonin sensitivity to dim light

The hormone melatonin is secreted at night from the pineal gland, with ligh t being a potent inhibitor of its secretion. Age related decreases in plasm a melatonin concentrations have indicated that this may be related to pinea l calcification with aging. Recently, it was shown that the melatonin sensi tivity to light may be a biological marker of bipolar disorder. However, on average, patients were older than the control group in most studies, and i t is not known if age has an effect on the melatonin suppression by light. To test this hypothesis, the present study investigated the effect of age o n the melatonin sensitivity to dim light (200 lux). Participants were group ed into three age groups. On the testing night, they were placed in a dark room from 21.00 h to 02.30 h. Light exposure was for an hour from midnight to 01.00 h. Blood samples were collected at regular intervals for measureme nt of plasma melatonin. No significant differences were found in the percen tage suppression of melatonin within the age groups defined in the present study (P > 0.5). No correlation,vas also found between age and percentage s uppression of melatonin (r(2) = 0.007; P > 0.1). Our results suggest that t he melatonin suppression by light (200 lux) is not affected by age. Int Cli n Psychopharmacol 14:189-192 (C) 1999 Lippincott Williams & Wilkins.