Abstract
In this field study, we analyzed the effects of the permanent shiftwork system on sleep of 141 journalists working in a press agency. Their tasks were characterized by highly mental and cognitive activities. We found that dephasing between the sleep-waking cycle and internal biological rhythms was followed by an alternation of the quality and quantity of sleep. These effects increased with aging. A significant correlation was found between work amount during the evening shift (6.30 p.m.-0.30 a.m.) and the sleep onset time. A descriptive model is proposed in which the performance rhythm interacts with the circadian rhythm of biological variables which might control sleep.
