Jokes about blanket hogs and stealing the covers aside, my practice is full of couples who report incompatibility with regard to sleep. And while certain conflicts may be due to relationship issues or personalityfactors, some of the mismatch between women and men during the night is most certainly due to sex differences in sleep and circadian physiology. Women & Sleep: A Guide for Better Health, a monograph recently published by the Society for Women’s Health Research (SWHR) Interdisciplinary Network on Sleep highlights the ways that sleep and circadian rhythms are different between women and men. Here are 4 ways that sleep and circadian rhythms differ between the sexes:
1. Insomnia is more common in women than men. Insomnia is defined as difficulty falling or staying asleep and/or the experience of non-restorative sleep. The sex difference in insomnia first emerges around the time of puberty, when girls show more than 2x the rate of insomnia than boys. In contrast, adolescent boys do not show the same association between sexual maturation and insomnia. Thus, although psychosocial factors, such as early school start times, increased social opportunities, and decreased parental involvement in setting bedtimes could be implicated in sleep disturbances in tweens and teens, female sex hormones associated with puberty and menarche also may play a role in the development of insomnia in girls. Sex differences in insomnia persist across the lifespan. Epidemiologic studies indicate that midlife women have about a 40% increased risk of insomnia than men, and women ages 65+ have more than a 70% increased risk of insomnia compared to men the same age.
2. Women are more likely to be “early birds” and men are more likely to be “night owls.” This sex difference may be driven by differential circadian rhythm physiology wherein women have shorter circadian cycle lengths, on average, than men. Other circadian rhythm dissimilarities include higher sleepiness levels during the night and lower levels during the day in women compared to men, as well as differences in the strength or “amplitude” of circadian rhythms. Sex differences in circadian rhythms have implications for how women and men experience circadian sleep disorders such as shift work sleep-wake disorder and jet lag. Further downstream effects on health may also be related to these circadian sex differences as shift work has been associated with increased risk of breast and endometrial cancers.
3. Sleeping pills can work differently in women than in men. Studies show that some hypnotic medications (e.g., zolpidem) are metabolized differently in women and men. Because of slower metabolism in women, the U.S. Food and Drug Administration (FDA) recommends that zolpidem be given at a dose no higher than 5mg in women, compared to doses up to 10mg in men. In addition to metabolic variance between the sexes, rat studies show different pharmacologic activity of zolpidem in female versus male brains. Since women are more likely to experience insomnia than men, sex differences in hypnotic agents have important implications for treatment of this common sleep disorder.
4. Sleep disorders can present differently in women than in men. Sex differences can play a role in manifestations of both common and rare sleep disorders. For instance, narcolepsy is a sleep disorder in which patients experience severe daytime sleepiness, episodic muscle weakness called cataplexy, and disturbed sleep-wake cycles. Geneticsand immunologic factors are believed to contribute to this disease. Women with narcolepsy show symptoms at a younger age than men, but also report a longer duration—by 12 years—between the onset of symptoms and proper diagnosis than men. Women with narcolepsy also have more sleepiness during the day than men when measured with objective sleepiness testing.
In contrast to narcolepsy which is estimated to occur in only 1% of the population, obstructive sleep apnea (OSA) is a very common sleep disorder, affecting about 24% of men and 9% of women. In this syndrome, patients experience multiple pauses in breathing during sleep. Consequences of sleep apnea include sleep fragmentation, low oxygen levels during sleep, daytime sleepiness, and cognitive impairment. Men with sleep apnea tend to report snoring and witnessed apneas, whereas women are more likely to describe symptoms like fatigue, insomnia, and depressed mood. An estimated 90% of women with obstructive sleep apnea remain undiagnosed, likely because women don't report the classic symptoms typical in men. In addition to presenting a diagnostic challenge, the sex differences in OSA have important implications for treatment. For instance, women typically require lower levels of continuous positive airway pressure (also known as CPAP, a device used to keep the airway open during sleep) than men and may also need smaller masks to deliver CPAP.
Growing evidence indicates that healthy sleep and circadian rhythms are critical to good health, and understanding physiologic sex differences can help promote healthy sleep in both women and men—and may also promote harmony in the bedroom as well.