Two hours of evening light produces significant circadian phase delay shifts in older adults

Abstract

Older adults have earlier sleep timing and altered timing of their circadian rhythms relative to their sleep timing compared with young adults. These differences are hypothesized to contribute to age-related sleep disruption, and therefore treatments that modify the timing of circadian rhythms have been proposed. Because light is the most powerful environmental signal that impacts the circadian system, we tested whether a short moderate intensity light exposure in the evening could alter the timing of circadian rhythms, thereby improving sleep quality. Ten healthy participants (6 women; mean age 63.3) who complained of early and/or frequent awakenings were studied in a 12-night study. They maintained an 8-h sleep episode at their preferred times for two weeks before the study, and those times were used to schedule their 8-h study sleep episodes. After 3 baseline days, circadian phase was assessed on days 4–5 using the dim light melatonin onset (DLMO). On the next 4 days, participants received a 2-h evening light exposure. The light exposure began 3 h before bedtime, and was delivered using a fixture on a desk in front of the seated participant. Half of the participants received standard polychromatic white light (4100 K) and half received blue-enriched polychromatic white light, with the same target photon density. Circadian phase was reassessed on days 9–10. On all but the circadian phase assessment days, the participants were allowed to go outside in the middle of each day. Sleep was recorded each night and waking EEG was recorded throughout each light exposure. The two light groups were not significantly different in sex composition, age, sleep times, or baseline DLMO times. During the light exposures, both groups showed similar increases in subjective and objective alertness. Following the 4 light exposures, both groups showed significant phase delays in DLMO timing and latency to REM sleep, and a significant shortening in the interval between DLMO and bedtime. However, there was no significant change in sleep efficiency or the duration of any sleep stage between baseline nights and the nights following the light exposures. In this semi-ambulatory study, we found that 2 h evening light exposures of moderate intensity on four consecutive evenings could produce significant increases in evening alertness and significant phase delay shifts in circadian rhythm timing, but the light treatment was ineffective at changing nighttime sleep quality. We thank SP Dunne, AM Guzik, J Row, EJ Silva, R Zhang, and the DSM Chronobiology Core for help collecting and analyzing the data. The study was funded by US NIH grant R01 AG06072, and was conducted in the Brigham& Women’s Hospital General Clinical Research Center, supported by NIH grant M01 RR02635; MM was supported by fellowships from the La-Roche and Novartis Foundations (Switzerland) and Jazz Pharmaceuticals (USA); KS was supported by NIH fellowships T32 HL07901 and F32 AG031690. The polychromatic white and blue enriched lamps were provided by Philips Lighting B.V. for use in this study.