Increased sensitivity of the circadian system to light in delayed sleep–wake phase disorder

Abstract

Key points This is the first study to demonstrate an altered circadian phase shifting response in a circadian rhythm sleep disorder. Patients with delayed sleep–wake phase disorder (DSWPD) demonstrate greater sensitivity of the circadian system to the phase‐delaying effects of light. Increased circadian sensitivity to light is associated with later circadian timing within both control and DSWPD groups. DSWPD patients had a greater sustained pupil response after light exposure. Treatments for DSWPD should consider sensitivity of the circadian system to light as a potential underlying vulnerability, making patients susceptible to relapse. Abstract Patients with delayed sleep–wake phase disorder (DSWPD) exhibit delayed sleep–wake behaviour relative to desired bedtime, often leading to chronic sleep restriction and daytime dysfunction. The majority of DSWPD patients also display delayed circadian timing in the melatonin rhythm. Hypersensitivity of the circadian system to phase‐delaying light is a plausible physiological basis for DSWPD vulnerability. We compared the phase shifting response to a 6.5 h light exposure (∼150 lux) between male patients with diagnosed DSWPD (n = 10; aged 20.8 ± 2.3 years) and male healthy controls (n = 11; aged 22.4 ± 3.3 years). Salivary dim light melatonin onset (DLMO) was measured under controlled conditions in dim light (<3 lux) before and after light exposure. Correcting for the circadian time of the light exposure, DSWPD patients exhibited 31.5% greater phase delay shifts than healthy controls. In both groups, a later initial melatonin phase was associated with a greater magnitude phase shift, indicating that increased circadian sensitivity to light may be a factor that contributes to delayed phase, even in non‐clinical groups. DSWPD patients also had reduced pupil size following the light exposure, and showed a trend towards increased melatonin suppression during light exposure. These findings indicate that, for patients with DSWPD, assessment of light sensitivity may be an important factor that can inform behavioural therapy, including minimization of exposure to phase‐delaying night‐time light.

Home versus laboratory assessments of melatonin production and melatonin onset in young adults complaining of a delayed sleep schedule

“…In our study, the association between higher non‐visual sensitivity to light and later circadian phase in late sleepers was measured with a laboratory test of melatonin suppression (Moderie, Van der Maren, & Dumont, ). That association was also found in recent studies on patients with delayed sleep–wake phase disorder (DSWPD), using other non‐visual responses to light such as light‐induced circadian phase shifts (Watson et al., ) and the pupillary light reflex (McGlashan et al., ). The association between light sensitivity and circadian phase suggests that indoor lighting at home may have a larger suppressing effect on melatonin secretion in individuals with a late sleep schedule, particularly those with a late circadian phase.…”

“…Melatonin suppression before bedtime was larger in delayed participants with a later DLMO, which is consistent with our previous observation of an association between non‐visual sensitivity to light and circadian phase in these subjects (Moderie et al., ). An association between non‐visual sensitivity to light and circadian phase is also supported by recent studies on DSWPD patients (McGlashan et al., ; Watson et al., ). Increased non‐visual sensitivity to light seems therefore to be an aetiological factor in the complaint of a delayed sleep schedule in “circadian” sleep‐delayed individuals.…”

Evening home lighting adversely impacts the circadian system and sleep

“…The average home would suppress melatonin by nearly 50% in the average person. Given that we studied light sensitivity in healthy adults, there is potentially even greater impact of home lighting for individuals with heightened circadian light sensitivity, such as children 24 , clinical populations (e.g., sleep 25 and mood disorders 26,27 ), or those taking medications that increase light sensitivity 28 . Greater light sensitivity would put individuals at potentially greater risk of circadian disruption, due to more labile circadian phase 29,30 .…”

Sleep Physiology, Circadian Rhythms, Waking Performance and the Development of Sleep-Wake Therapeutics

“…Abnormal light exposure patterns are observed in delayed sleep-wake disorders (Van der Maren et al 2018;Wilson et al 2018). Furthermore individual differences in the circadian sensitivity to light are emerging (Santhi et al 2012) and increased sensitivity to light may be a characteristic of delayed sleep-wake phase syndrome (DSPS) (Watson et al 2018).…”