Sleep is critical for our health and wellbeing. But with poor sleep becoming a growing problem around the world, it's more important now than ever to understand what factors affect sleep quality.
Author
Sarah Chellappa
Associate Professor, Cognitive and Affective Neuroscience, University of Southampton
Surprisingly, one factor that affects how well a person sleeps at night is their sex. Research shows sleep problems appear to be more common in women. Other studies have also shown women may be more affected by circadian rhythm disruptions (the almost 24-hour cycle that controls many of our body's processes) compared to men.
But there's still a lot we don't know about how men and women might differ when it comes to sleep and the circadian rhythm - and what effect such differences may have on health.
This is what a new review conducted by myself and my colleagues sought to uncover. We revealed key differences in sleep quality and circadian rhythm function in men and women. We also found that these factors may affect metabolism, which could have long-term effects on a person's health and risk of certain diseases.
Body clock differences
To conduct our review, we assessed around 150 articles, most of which were published in the last decade, that explored different aspects of sleep, circadian rhythms and metabolism, as well as a few studies on potential sex differences in relation to these aspects.
We revealed some key differences in how women and men sleep - finding variations in their circadian rhythms as well as the way their metabolism functions as a result.
We showed that women tend to report lower quality sleep compared to men. We also found that their quality of sleep tended to fluctuate more than men's did.
Moreover, our review revealed women are up to 50% more likely than men to develop certain sleep disorders, such as restless leg syndrome. On the other hand, men are up to three times more likely to be diagnosed with sleep apnoea than women are. However, this may be due to differences in how the condition presents itself in women compared to men.
Our review also showed that differences between men and women don't only exist for sleep and sleep problems.
Melatonin, a hormone that helps with the timing of circadian rhythms and sleep, is secreted a bit earlier in women compared to men. Internal body temperature, which is at its highest before sleep and its lowest a few hours before waking up, follows a similar pattern - with the body temperature peak shown to happen earlier in women than men. This might help explain why women tend to prefer earlier sleep times compared to men.
But men tend to prefer going to sleep and waking up later, which may clash with social demands, such as work.
Overall, women reported worse sleep quality on average and were at higher risk of insomnia. Men, however, were at greater risk of developing sleep apnoea.
Metabolism changes
Sleep quality and the circadian rhythm both have strong effects on metabolism, with previous research showing a link between circadian rhythm disruption and higher risk of metabolic diseases, such as obesity and type 2 diabetes. So, our review also investigated the link between these two factors and metabolism - and whether this also differed in men and women.
We found that women's and men's brains respond differently to pictures of food when they're sleep deprived. We revealed that brain areas associated with emotion are twice as active in sleep-deprived women than in sleep-deprived men. But men who were sleep deprived reported feeling hungrier than women. These responses might suggest it could affect a person's eating choices the next day - such as what foods they choose to eat and how much they eat. But it will be important for future studies to test this idea.
Our review also identified links between circadian rhythm disruption and metabolic disease.
We found that people who worked nightshifts were more likely to be diagnosed with type 2 diabetes compared to those who worked during the day. But a man's risk of developing type 2 diabetes was twice as high when working night shifts than a woman's.
But female night shift workers were shown to be around one-and-a-half times more likely to be overweight or obese compared to women who worked day shifts.
These findings all show just how important sleep and circadian rhythms are when it comes to our metabolism and risk of certain diseases, including diabetes and those related to body weight.
Overall, these findings reinforce what other studies before us have shown, which is that biological sex can affect many aspects of sleep - including the quality of sleep a person gets each night, what sleep problems they may be at greater risk of developing and how their body responds to sleep deprivation.
Our findings also highlight the need to tailor treatment for sleep and circadian rhythm disorders depending on a person's sex - with our research highlighting some of the possible reasons why women and men may respond differently to existing treatments.
But though the evidence is beginning to show how a person's sex can affect their circadian rhythm and quality of sleep they get, there's a lot we still don't know. This is largely due to the under-representation of women in sleep and circadian rhythm research. It's also currently unknown what specific mechanisms explain why sleep and circadian rhythm problems are linked to greater risk of certain health conditions, and why sleep and circadian rhythm differ between women and men.
We also need to consider the menstrual cycle and contraceptive use when designing studies, as they affect sleep and circadian rhythms.
By investigating these issues, we may be better able to understand why these differences exist between men and women when it comes to sleep and health - and may be better equipped to provide more effective treatments for women and men.
Sarah Chellappa does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
