Abstract
BackgroundOur aims were to examine the influence of different bright light schedules on mood, sleep, and circadian organization in older adults (n = 60, ages 60–79 years) with insomnia and/or depression, contrasting with responses of young, healthy controls (n = 30, ages 20–40 years).MethodsVolunteers were assessed for one week in their home environments. Urine was collected over two 24-hour periods to establish baseline acrophase of 6-sulphatoxymelatonin (aMT6s) excretion. Immediately following home recording, volunteers spent five nights and four days in the laboratory. Sleep periods were fixed at eight hours in darkness, consistent with the volunteers' usual sleep periods. Volunteers were randomly assigned to one of three light treatments (four hours per day) within the wake period: (A) two hours of 3,000 lux at 1–3 hours and 13–15 hours after arising; (B) four hours of 3,000 lux at 6–10 hours after arising; (C) four hours of dim placebo light at 6–10 hours after arising. Lighting was 50 lux during the remainder of wakefulness. The resulting aMT6s acrophase was determined during the final 30 hours in the laboratory.ResultsNeither mood nor total melatonin excretion differed significantly by treatment. For the three light treatments, significant and similar phase-response plots were found, indicating that the shift in aMT6s acrophase was dependent upon the circadian time of treatment. The changes in circadian timing were not significantly correlated to changes in sleep or mood.ConclusionThe trial failed to demonstrate photoperiodic effects. The results suggest that even low levels of illumination and/or fixed timing of behavior had significant phase-shifting effects.
Highlights
Older adults have an altered synchronization of circadian rhythms compared to young adults [1,2,3,4]
It is likely that retinohypothalamic neurotransmission of light to the suprachiasmatic nuclei (SCN) is compromised in older adults due to glaucoma, macular degeneration, senile miosis, and other eye problems [8,9]
Doseresponse studies have indicated that phase-shifting effects of light are related to cube-root [27] or logistic functions [28] of illumination, either of which would predict that the bright light treatments (3,000 lux) were at least twofold stronger than the placebo treatment (50 lux)
Summary
Older adults have an altered synchronization of circadian rhythms compared to young adults [1,2,3,4]. Circadian misalignment of rhythms or malsynchronization might contribute to many age-related disorders of sleep or mood, as has been observed in conjunction with shift-work and jet lag. Studies have found that, when compared to young adults, older adults are exposed to at least as much bright light (e.g., in San Diego [5,6]) and to environmental and social zeitgebers of even greater regularity [7]. Our aims were to examine the influence of different bright light schedules on mood, sleep, and circadian organization in older adults (n = 60, ages 60–79 years) with insomnia and/or depression, contrasting with responses of young, healthy controls (n = 30, ages 20–40 years)
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