Effects of afternoon "siesta" naps on sleep, alertness, performance, and circadian rhythms in the elderly

Study objectives: To determine the effects of a 90-minute afternoon nap reg imen on nocturnal sleep, circadian rhythms, and evening alertness and perfo rmance levels in the healthy elderly. Design and Setting: Nine healthy elderly subjects (4m, 5f, age, range 74y - 87y) each experienced both nap and no-nap conditions in two studies each l asting 17 days (14 at home, 3 in the laboratory). In the nap condition a 90 -minute nap was enforced between 13:30 and 15:00 every day, in the no-nap c ondition daytime napping was prohibited, and activity encouraged in the 13: 30-15:00 interval. The order of the two conditions was counterbalanced. Participants: N/A Interventions: N/A Measurements: Diary measures, pencil and paper alertness tests, and wrist a ctigraphy were used at home. In the 72 hour laboratory studies, these measu res were augmented by polysomnographic sleep recording, continuous rectal t emperature measurement, a daily evening single trial of a Multiple Sleep La tency Test (MSLT), and computerized tests of mood, activation and performan ce efficiency. Results. By the second week in the "at home' study, an average of 58 minute s of sleep was reported per siesta nap; in the laboratory, polysomnography confirmed an average of 57 minutes of steep per nap. When nap and no-nap co nditions were compared, mixed effects on nocturnal sleep were observed. Dia ry measures indicated no significant difference in nocturnal sleep duration , but a significant increase (of 38 mins.) in 24-hour Total Steep Time (TST ) when nocturnal sleeps and naps were added together (p<0.025). The laborat ory study revealed a decrease of 2.4% in nocturnal sleep efficiency in the nap condition (p<0.025), a reduction of nocturnal Total Sleep Time (TST) by 48 mins. in the nap condition (p<0.001) which resulted primarily from sign ificantly earlier waketimes (p<0.005), but no reliable effects on Wake Afte r Sleep Onset (WASO), delta sleep measures, or percent stages 1 & 2. Unlike the diary study, the laboratory study yielded no overall increase in 24-ho ur TST consequent upon the siesta nap regimen. The only measure of evening alertness or performance to show an improvement was steep latency in a sing le-trial evening MSLT (nap: 15.6 mins., no nap: 11.5 mins., p<0.005). No si gnificant change in circadian rhythm parameters was observed. Conclusions: Healthy seniors were able to adopt a napping regimen involving a 90-minute siesta nap each day between 13:30 and 15:00, achieving about o ne hour of actual steep per nap. There were some negative consequences for nocturnal sleep in terms of reduced sleep efficiency and earlier waketimes, but also some positive consequences for objective evening performance and (in the diary study) 24-hour steep totals. Subjective alertness measures an d performance measures showed no reliable effects and circadian phase param eters appeared unchanged.