DOES A SUBTROPICAL CLIMATE IMPLY A SEASONAL RHYTHM IN REM-SLEEP

The present study was performed on 615 male subjects referred to the S leep 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-Janua ry 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 tim e and REM sleep percentage were higher and REM sleep latency shorter d uring winter and spring than during summer and fall. No dependence of the seasonal REM sleep time rhythm upon age, apnea-hypopnea index or d iagnosis type was detected. These data support, for a subtropical clim ate, results previously obtained in a temperate climate. It is possibl e that external temperature may be the principal factor influencing th e phenomenon.