Does a subtropical climate imply a seasonal rhythm in REM sleep?

Abstract

The present study was performed on 615 male subjects referred to the Sleep Medicine Center at Tel Hashomer, Israel, and polysomnographically recorded for a single night between January 1, 1990 and December 31, 1993. The study suggests the existence of a circannual rhythm of rapid eye movement (REM) sleep time with an acrophase during December-January and a nadir during July-September (single cosinor analysis: mesor = 49.7 +/- 0.9, amplitude = 5.9 +/- 1.2, p < 0.001). Both REM sleep time and REM sleep percentage were higher and REM sleep latency shorter during winter and spring than during summer and fall. No dependence of the seasonal REM sleep time rhythm upon age, apnea-hypopnea index or diagnosis type was detected. These data support, for a subtropical climate, results previously obtained in a temperate climate. It is possible that external temperature may be the principal factor influencing the phenomenon.