Background: Disturbances in rest–activity rhythm are prominent and disabling symptoms in Alzheimer's disease (AD). Nighttime sleep is severely fragmented and daytime activity is disrupted by multiple napping episodes. In most institutional environments, light levels are very low and may not be sufficient to enable the circadian clock to entrain to the 24-hour day. The purpose of this randomized, placebo-controlled, clinical trial was to test the effectiveness of morning bright light therapy in reducing rest–activity (circadian) disruption in institutionalized patients with severe AD.

Method: Subjects (n=46, mean age 84 years) meeting the NINCDS-ADRDA (National Institute of Neurological and Communicative Disorders and Stroke – the Alzheimer's Disease and Related Disorders Association) AD diagnostic criteria were recruited from two large, skilled nursing facilities in San Francisco, California. The experimental group received one hour (09:30–10:30) of bright light exposure (≥2500lux in gaze direction) Monday through Friday for 10weeks. The control group received usual indoor light (150–200lux). Nighttime sleep efficiency, sleep time, wake time and number of awakenings and daytime wake time were assessed using actigraphy. Circadian rhythm parameters were also determined from the actigraphic data using cosinor analysis and nonparametric techniques. Repeated measures analysis of variance (ANOVA) was used to test the primary study hypotheses.

Results and conclusion: Although significant improvements were found in subjects with aberrant timing of their rest–activity rhythm, morning bright light exposure did not induce an overall improvement in measures of sleep or the rest–activity in all treated as compared to control subjects. The results indicate that only subjects with the most impaired rest–activity rhythm respond significantly and positively to a brief (one hour) light intervention.