[Effects of continuous lighting on secretion of melatonin and pituitary hormones in women]

Effects of light exposure on the serum concentrations of melatonin, prolactin, LH and FSH were studied in 53 women during their follicular phases. Twenty seven women were exposed to light (500-800 lux at eye level) from 17:30h to 22:00h, and 17 women received the same light intensity from 17:30h to 2:00h, while 9 women stayed in a dark room from 21:00h to 2:00h as control subjects. The light exposure suppressed a nocturnal increase in the serum concentrations of melatonin both at 22:00h and 2:00h. The light exposure and awake condition suppressed the serum prolactin concentrations and increased the serum FSH concentrations at 2:00h, while the influence on the serum LH concentrations was not clear because of LH pulsatility. These results show that the circadian rhythm of melatonin, prolactin and FSH is affected by light exposure and wakefulness, and the effects of light exposure would become more evident if light exposure was continued over a longer period.