Timing of light exposure and activity in adults with delayed sleep-wake phase disorder.

OBJECTIVE: To characterize the patterns of light exposure and physical activity level and assess their relationship with sleep quality and depressive symptoms in adults with delayed sleep-wake phase disorder (DSWPD).

METHODS: 42 DSWPD (22 female, mean age 34.5 y) and 26 (±4 years) age-and-sex-matched controls (12 female, mean age 33.4 y) underwent seven days of light and activity monitoring.

RESULTS: Individuals with DSWPD had significantly delayed bed times and wake times, but similar sleep duration compared to controls. Subjective sleep quality (Pittsburgh Sleep Quality Index (PSQI)) was poorer in DSWPDs compared to controls. Those with DSWPD had significantly more activity and light exposure late at night (2:00-4:00) and significantly less activity and light exposure in the morning (8:00-11:00). Total 24 h levels of light and activity were not significantly different between DSWPD and controls. However, the DSWPD group had significantly more light exposure than controls 22 h after waking, during their sleep period. Later light exposure correlated with higher depression scores [Beck Depression Index (BDI)] and poorer sleep quality (PSQI).

CONCLUSIONS: The light exposure patterns observed in DSWPD likely contribute to and perpetuate the chronically delayed sleep and wake phase in these patients. In addition, increased light exposure during the sleep period may also contribute to the poor sleep quality and mood disorders that are common in these individuals.