Diminished capability to recognize the optimal temperature for sleep initiation may contribute to poor sleep in elderly people

Abstract

Study objectives: Sleep propensity and skin temperature are functionally related. In young adults, changes of skin temperature within the comfortable thermoneutral zone affect sleep-onset latency and vigilance performance. Aging is associated with both decreased thermosensitivity and poorer sleep. Our goal was to test whether subtle manipulations of core body and skin temperature affect sleep onset in elderly people without sleep complaints and in elderly insomniacs and whether the subjective perception of these mild body temperature manipulations is preserved with aging and insomnia.

Design: In a 2-day semiconstant-routine protocol, 288 sleep-onset latencies were polysomnographically determined while manipulating core body and skin temperatures differentially in warm and cold directions within a comfortable thermoneutral range.

Setting: Sleep laboratory of the Netherlands Institute for Neuroscience.

Patients or participants: Eight elderly subjects without sleep complaints (65.8 +/- 2.8 years, mean +/- SEM) and 8 elderly insomniacs (59.1 +/- 1.9 years).

Measurements and results: Warming the proximal skin by 0.4 degrees C facilitates sleep onset equally effective in healthy elderly (by 18% ie, by 1.84 minutes [95% confidence interval [CI], 0.76-2.92]) and elderly insomniacs (28%, 2.85 minutes [CI: 2.55-3.18]). These effects were comparable to the results in healthy young subjects, in spite of a marked decrease in the subjective perception of temperature changes in elderly subjects, especially in insomniacs.

Conclusion: The findings show that mild changes in skin temperature have an effect on sleep propensity in elderly and indicate that elderly insomniacs may have a diminished capability to recognize that a slight increase in bed temperature facilitates the initiation or reinitiation of sleep.

Figure 1

Schematic view of the temperature manipulations within one day within one subject. Core body, proximal and distal skin manipulation occurs simultaneously during every block. Within the last 30 minutes of each block the MSLT was performed. On the 2^nd day, temperature manipulation combinations were the opposite of those of the 1^st day to provide a protocol balanced for circadian effects. Block A: Habituation block. White represents cool; dark gray represents warm.

Figure 2

Sleep onset latencies (± 95% confidence intervals) in elderly and elderly insomniacs. Effect sizes follow from the regression analysis results presented in table 4.