Weak evidence of bright light effects on human LH and FSH

To gain further information on effects of bright light on LH and FSH secretion in humans, we analyzed urine samples collected in three experiments conducted for other goals. First, volunteers ages 18-30 years and 60-75 commenced an ultra-short 90-min sleep-wake cycle, during which they were exposed to 3000 lux light for 3 hours at balanced times of day, repeated for 3 days. Urine samples were assayed to explore any LH phase response curve. Second, depressed participants 60-79 years of age were treated with bright light or dim placebo light for 28 days, with measurements of urinary LH and FSH before and after treatment. Third, women of ages 20-45 years with premenstrual dysphoric disorder (PMDD) were treated to one 3-hour exposure of morning light, measuring LH and FSH in urine before and after the treatments.Two of the three studies showed significant increases in LH after light treatment, and FSH also tended to increase, but there were no significant contrasts with parallel placebo treatments and no significant time-of-day treatment effects.These results gave some support for the hypothesis that bright light may augment LH secretion. Longer-duration studies may be needed to clarify the effects of light on human LH and FSH.Several generations of scientists have studied photoperiodism extensively throughout the biological world. One of the most dramatic photoperiodic responses in birds is a massive increase in luteinizing hormone (LH) appearing within a few hours of stimulatory light exposure at a critical time of night [1]. Likewise, in small mammals, light at critical times of night produces large increases in LH and follicle stimulating hormone (FSH), resulting in growth of gonads [2-4]. These increases in gonadotropins prepare animals for seasonal breeding [5]. There is a preponderance of evidence that light at night functions to decrease the duration of melatonin secretion, causing the nights to be interpreted as shorter (complementing a longer summer-like day)