Stability of day and night sleep--a two-year follow-up of EEG parameters in three-shift workers.

Twenty rotating three-shift workers participated. Night and day sleep in connection with work on afternoon and night shifts, respectively, were recorded using 24-hour polysomnographic recording techniques. The procedure was repeated 2 years later. Both day and night sleep showed high significant correlations between years for rapid eye movement (REM) sleep, slow wave sleep (SWS-stages 3 + 4), total sleep time, slow wave energy, in the delta band (obtained via spectral analysis) and subjective sleep quality. Stage 2, stage 1, percent waking, sleep latency, SWS latency and REM latency were not correlated across years. None of the variables showed a significant difference between years. It was concluded that core variables of sleep show considerable interindividual stability across time and that a 2-year exposure to rotating shift work does not affect sleep in experienced shift workers.