Strategies for Resetting the Human Circadian Clock

Night work, which is voluntarily accepted by millions of workers in industrialized countries, is a major health hazard, involving an increased risk of cardiovascular illness, gastrointestinal disorders, infertility, and insomnia. The medical consequences of night work are associated with chronic misalignment of physiologic circadian rhythms and the activity–rest cycle. Indeed, as Czeisler et al.¹ indicate in this issue of the Journal, several studies have shown that workers on permanent or rotating night shifts generally do not adapt to these schedules, even after several years. The inability to adapt appears to be due to the fact that the endogenous timing…