Extraocular light exposure does not phase shift saliva melatonin rhythms in sleeping subjects

Abstract

Preliminary work in humans suggests that extraocular light can shift circadian phase. If confirmed, extraocular light may be of therapeutic benefit in the treatment of circadian-related sleep disorders with the advantage over ocular exposure that it can be administered while subjects are asleep. In sleeping subjects, however, the effect of extraocular light exposure on circadian phase has yet to be fully tested. Likewise, there is limited data on the acute effects of extraocular light on sleep and body temperature that may influence its clinical utility. Thirteen subjects [3F, 10M; mean (SD) age = 22.1 (3.0)y] participated in a protocol that totaled 7 nights in the laboratory consisting of a screening phase measurement night followed 1 week later by two counterbalanced experimental sessions each of 3 consecutive nights (habituation, treatment, and posttreatment phase measurement night) separated by 4 days. Saliva was collected for melatonin measurement every half hour from 1800 to 0300 h on the screening night and both the posttreatment phase measurement nights. On the treatment nights, continuous measures of rectal temperature and polysomnographic sleep were collected and overnight urine for measurement of total nocturnal urinary 6-sulphatoxymelatonin excretion. To test for the phase-delaying effects of extraocular light, subjects received either placebo or extraocular light (11,000 lux) behind the right knee from 0100 to 0400 h. Treatment had no significant effect on the onset of saliva melatonin secretion, phase of nocturnal core body temperature, or urinary 6-sulfatoxymelatonin excretion, but a small increase was observed in wakefulness over the light administration period. In summary, extraocular light was not shown to delay circadian phase but was shown to increase wakefulness. The authors suggest that the present protocol has limited application as a treatment for circadian-related sleep disorders.