Circadian Rhythm Disorders: Does Sex Matter?

Abstract

There are sex-related differences in circadian rhythms with women having shorter intrinsic periods and earlier phase of both temperature and melatonin rhythms relative to men. Although still equivocal, women may also have different amplitudes of their temperature rhythms, but the extent of the difference appears to depend on menstrual cycle phase and age. These sex-related differences may be due to differences in output of the suprachiasmatic nucleus, which has sex steroid receptors, or due to differences downstream of the circadian pacemaker. Sex-related differences in the prevalence of circadian rhythm sleep disorders require further study although it appears that men and women are equally likely to experience advanced and delayed sleep phase syndrome. However, men are more than two times more likely than women to suffer from non-24-h sleep–wake syndrome. Limited evidence indicates that men and women adapt equally well physiologically to shift work but women show more symptoms of intolerance and greater sleep difficulties than men possibly because of social factors such as maternal responsibilities, which add to the workload and reduce time for sleep. There are special concerns for health-related consequences of shift work in women given that female shift workers are at increased risk for breast cancer, fertility problems, and preterm births compared with female nonshift workers.

Keywords

Body temperature,Melatonin,Menstrual cycle,Phase angle of entrainment,Shift work