Medical implications of shift-work.

The circadian pacemakers, which time the approximately 24-hour rhythms in sleep and wakefulness, neuroendocrine, thermoregulatory, and other body functions, resynchronize only slowly after an abrupt phase shift in environmental time cues. While the symptoms of jet-lag are transient, the kinds of repeated shifts over a number of years experienced by shift-workers on rotating schedules induce sleep-wake disorders, gastrointestinal pathology, and an increased risk of cardiovascular disease. There is significant interindividual variation in the ability to adapt and also a deterioration with age. Evidence is accumulating that poor adapters present with a Shift Maladaption Syndrome with characteristic pathological manifestations.