Shift work, jet lag, and female reproduction

In mammals, the 24-hour clock mechanism, or circadian oscillator, is critical for the function and coordination of a broad range of biological processes, from hormone secretion to locomotor activity. This biological timing system is vital for successful reproduction. Animals are more likely to gain mating opportunities if they coordinate their sexual behavior with that of their potential partners. Females benefit from synchronizing the timing of pregnancy to seasons with favorable food and weather conditions, and it is advantageous for an animal to give birth at a time of day when it is most likely to be in a safe place such as a burrow rather than out foraging. A mounting body of evidence indicates that disruptions in normally synchronized, or entrained, biological rhythms are associated with a broad range of pathologies including reproductive dysfunction in females.