Sleep-wake patterns and subjective sleep quality of day and night workers: interaction between napping and main sleep episodes.

Five hundred and ninety-three women electronics workers were studied to determine if there was any association between their subjective sleep quality and their sleep patterns. They were 108 day workers, 107 permanent night workers, 216 workers on weekly phase-advance (night/afternoon/morning), and 162 workers on two-weekly phase-delay (morning/afternoon/night) rotating shift schedules. The study was part of a larger survey on night workers involving a self-administered questionnaire. The proportion of nappers was higher in night workers than in day, morning, and afternoon shift workers. Nappers had shorter main sleep, but their total sleep duration was generally the same as that of nonnappers. Compared to nonnappers, a higher proportion of day and morning shift workers who napped did not sleep well. Permanent night workers, with the highest proportion of nappers, had more workers sleeping well than rotating night workers. Subjects who slept well were those with longer total and main sleep and generally started the main sleep earlier. The results indicate a relationship between subjective sleep quality, sleep length, main sleep start, and napping behavior. Whether this relationship is causal is difficult to establish as sleep quality may also reflect the general health status, and this may result in differences in sleep behavior.