Relationships between sleep and body temperature in middle-aged and older subjects

Although changes in the circadian timing system are thought to be a major factor in the decline of sleep quality that often accompanies aging, few reports have actually examined this relationship in detail. Because some treatments for age-related insomnia are based on putative circadian changes, it is important to expand the limited database that specifically addresses this issue. This study examined age-related changes in sleep, and relationships between those sleep changes and alterations in the circadian timing system, in a group of middle-aged and older subjects.

Sixty healthy men and women between the ages of 40 and 84 were studied. A subset of older subjects (< 65 years) had reported sleep disturbance for at least 1 year before participation. Polysomnography was obtained, and body core temperature was recorded continuously for 24 hours. All recordings took place in the Laboratory of Human Chronobiology, Department of Psychiatry, Cornell University Medical College.

There were no differences in sleep quality between middle-aged and non-sleep-disturbed older subjects. However, timing of the minimum body temperature was earlier in the older non-sleep-disturbed subjects than in the middle-aged group. In contrast, sleep-disturbed older people had shorter total sleep times, reduced sleep efficiency, more waking time after sleep onset, and a reduced proportion of REM sleep compared with non-sleep-disturbed older subjects. Yet, there were no differences between the two older groups in the rhythm of body temperature. For the entire group, age was correlated negatively with total sleep time, sleep efficiency, percentage of stage 2 sleep, and the timing of the temperature minimum.

The results support the widely held notion that sleep and circadian rhythm changes occur with aging. However, the hypothesis that age-related changes in sleep may be associated with aging of the circadian system was supported only to a limited degree, suggesting that age-related sleep disturbance is likely to have multiple causes. Thus, treatment strategies that incorporate a combination of interventions may be the most effective.