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Abstract
Patients with delayed sleep phase syndrome (DSPS) experiencea chronic mismatch between the usual daily schedule required by the individual'senvironment and their circadian sleep-wake pattern, resulting in major academic,work, and social problems. Although functional abnormalities of the circadianpacemaker system have been reported in patients with DSPS, the etiology ofDSPS has not been fully elucidated. One hypothesis proposed to explain whypatients with DSPS fail to synchronize their 24h sleep-wake cycle to theirenvironment is that they might have reduced sensitivity to environmental timecues, most notably light-dark cycles. Therefore, we compared the sensitivityof melatonin suppression in response to light in patients with DSPS and normalcontrol subjects. Fifteen patients with DSPS and age- and sex-matched healthycontrols were studied. As the melatonin secretion rhythm in patients withDSPS was expected to be delayed compared to the controls, the time of peakmelatonin secretion was determined in each subject in the first session. Inthe second session, each subject was exposed to light with an intensity of1000 lux for 2h beginning 2h prior to his or her peak melatonin secretion.Melatonin was measured by radioimmunoassay in saliva sampled every 30 minutesduring the period of light exposure. Suppression of the melatonin concentrationin saliva was dependent on duration of light exposure. In addition, the suppressiveeffect of light on the melatonin concentration was significantly greater inpatients with DSPS than in control subjects. The results suggest hypersensitivityto nighttime light exposure in patients with this syndrome. Our findings thereforesuggest that evening light restriction is important for preventing patientswith DSPS from developing a sleep phase delay. (ChronobiologyInternational, 18(2), 263–271, 2001)