Of Sex and Sleep: Exploring Sex Differences in Sleep Health and Research
By: Ekaterina An
Dr. Gillian Einstein, PhD
Associate Professor, Department of Psychology, University of Toronto
Associate Professor, and Dalla Lana School of Public Health, University of Toronto
Director of the Collaborative Graduate Program in Women’s Health, University of Toronto
Adjunct Scientist, Women’s College Research Institute
Member, Institute of Medical Science
In 2009, Health Canada introduced the Sex and Gender-Based Analysis Policy that required numerous health research organizations, including the Canadian Institutes of Health Research (CIHR), to “develop, implement and evaluate research, programs and policies to address the different needs of women and men.”1 This mandate reflected the importance of understanding the health determinants of both sexes, and was followed by a 2010 CIHR and 2014 National Institutes of Health requirement that applicants discuss whether their study included sex or gender. When it comes to sex and sleep, a number of studies have identified differences in sleep quality between men and women. For example, Zhang and Wing2 found that women were more likely to experience insomnia than men, a trend that remained consistent and progressive across age groups. Further research into sleep differences reported that women’s 24-hour circadian rhythms are markedly different from men3 and that differences in sleep quality between sexes only become apparent following the onset of puberty.4 These results all point to a potential hormonal explanation for the differences in sleep quality between sexes, but there is a lack of consensus regarding the nature of this link: some studies were able to demonstrate an association between sleep quality and estradiol (an ovarian hormone), while others found no associations between the two.5
Dr. Gillian Einstein, an associate professor in the Department of Psychology and in the Dalla Lana School of Public Health, and the Director of the Collaborative Graduate Program in Women’s Health at the University of Toronto, is no stranger to this entanglement of sex and sleep differences. “Sleep is very complex,” she says, laughing. Dr. Einstein’s current research interests center around women’s health, and incorporating sex and gender into basic science and clinical research. But her interest in sleep was first piqued about 15 years ago when she heard Dr. Allan Hobson, a prominent sleep researcher, address some of her students on the importance of conducting sleep research. “At that time, sleep was under-researched, he [Dr. Hobson] thought, because people thought it was voyeuristic. You were studying people when they were vulnerable and unaware, but he said it was incredibly important for health because somebody could go to the doctor awake and not have any heart problems, and somebody could be sleeping and they would have tachycardia,” Dr. Einstein says.
Given the murky picture of the interaction between sleep and sex and her interest in women’s health in particular, Dr. Einstein set out to explore the relationships within the triad of hormones, mood, and sleep in women. The latter two factors – mood and sleep – have been linked: disturbed sleep is a hallmark of many mood disorders.6 Similarly, hormones and mood are associated with one another, with women of reproductive age reporting mood variations that align with the menstrual cycle.7 However, there is a lack of consensus on the influence of hormones on sleep quality.
Alongside her colleague, Dr. Sarah Romans, Dr. Einstein conducted the Sleep and Mood in Daily Life study in non-help-seeking, community-dwelling women.5,8 They collected data on mood, urinary estrogen and progesterone concentrations, and self-reported and objective measures of sleep quality from 19 women aged 18 – 43 years old.5 The study, published in Sleep Medicine, found that sleep quality generally did not correlate with hormone levels, but was strongly correlated with mood.5 Only objective measures of sleep were found to correlate slightly with ovarian hormone levels.5 Contrary to some reports in the literature on the relationship between female hormones and sleep, Dr. Einstein and her team found that estrogen and progesterone played an insignificant role in daily sleep variation.5 “Women feel they’re getting not as much sleep as they should and it’s poor quality, but in the group we studied it’s not something that is related to the menstrual cycles or hormones by the objective measures we used,” says Dr. Einstein.
While the link between sleep quality and ovarian hormones in healthy women was minimal, there was a strong correlation of sleep quality with perceived mood. Women who felt that they were “Feeling ” reported higher sleep quality, while those who felt that they had “Difficulty Coping” reported poorer sleep.5 This finding is consistent with previous reports on the association between sleep quality and affect.6 Interestingly, mood and hormones did not correlate in this cohort of women. Thus, although sleep quality was highly contingent on mood, perceived mood was unaffected by the menstrual cycle9 or levels of ovarian hormones – a finding that surprised Dr. Einstein: “We came out of that study thinking that PMS [premenstrual syndrome whose symptoms include mood swings, fatigue, and irritability] 10 was probably something that was more socially constructed.” One explanation for this lack of association between mood and hormones in this sample may be the fact that this cohort of women differed from the traditional study participant in that they were non-help-seeking (participants were recruited using random-digit dialing), a fact that may influence how women perceive their own sleep quality and mood. Additionally, Dr. Einstein believes that hiding the menstrual cycle focus of the study may have mitigated the risk of confirmation bias in participant responses. She also notes that while estrogen may have a direct effect on neurons, there are a multitude of brain regions and social factors that influence one’s mood, such that some neuronal responses might be negated by others that are unaffected by estrogens.
The lack of correlation between sleep and hormones in Dr. Einstein’s study does not discourage her from pursuing further research in this field. She believes that estrogens do have a direct effect on neurons, and is interested in studying sleep quality and sleep patterns in women who have had their ovaries removed prior to natural menopause. Currently working with this group of women, Dr. Einstein says, “Of course they talk about sleep problems, a lot. And it’s hard to know whether their sleep problems are because of estrogen withdrawal leading to hot flashes and such – or whether it’s actually that estrogen withdrawal affects the parts of the brain that are involved in sleep or might actually play a role in creating sleep apnea.”
Although women continue to report poorer sleep quality than men, they have historically been under-represented in sleep research.11 As more differences between male and female sleep patterns are coming to light, it is clear that this field of research would benefit from further exploration of the sex and gender differences in sleep quality. Dr. Einstein encourages researchers from all disciplines to consider sex and gender effects in both pre-clinical and clinical studies. For those looking to learn more about the impact of gender and sex on health, Dr. Einstein’s course, Gender and Health (CHL5109H), examines the clinical and social implications of women’s health research and gender-based medicine.
- Health Canada [Internet]. [Canada]: Government of Canada, 2009 [updated 2010 Mar 12; cited 2016 May 10]. Available from: http://www.hc-sc.gc.ca/hl-vs/pubs/women-femmes/sgba-policy-politique-ags-eng.php
- Zhang B, Wing Y. Sex differences in insomnia: a meta-analysis. Sleep 2006 Jan 1; 29(1):85.
- Duffy JF, Cain SW, Chang AM, Phillips AJ, Münch MY, Gronfier C, Wyatt JK, Dijk DJ, Wright KP, Czeisler CA. Sex difference in the near-24-hour intrinsic period of the human circadian timing system. Proc. Natl. Acad. Sci. 2011 Sep 13; 108(Supplement 3):15602-8.
- Krishnan V, Collop NA. Gender differences in sleep disorders. Curr. Opin. Pulm. Med. 2006 Nov 1;12(6):383-9.
- Li DX, Romans S, De Souza MJ, Murray B, Einstein G. Actigraphic and self-reported sleep quality in women: associations with ovarian hormones and mood. Sleep Med. 2015 Oct 31;16(10):1217-24.
- Benca RM, Okawa M, Uchiyama M, Ozaki S, Nakajima T, Shibui K, Obermeyer WH. Sleep and mood disorders. Sleep Med. Rev. 1997 Nov 30;1(1):45-56.
- Rubinow DR, Roy-Byrne P, Hoban MC, Grover GN, Stambler N, Post RM. Premenstrual mood changes: characteristic patterns in women with and without premenstrual syndrome. J. Affect. Disord. 1986 Mar 1;10(2):85-90.
- Romans SE, Kreindler D, Einstein G, Laredo S, Petrovic MJ, Stanley J. Sleep quality and the menstrual cycle. Sleep Med. 2015 Apr 30;16(4):489-95.
- Schwarz S, Hassebrauck M. Self-perceived and observed variations in women’s attractiveness throughout the menstrual cycle—a diary study. Evol. Hum. Behav. 2008 Jul 31; 29(4):282-8.
- Frequently asked questions. Gynecologic problems FAQ057. Premenstrual syndrome. [Internet] [Washington, DC]: American College of Obstetricians and Gynecologists, 2015 [cited 2016 May 10]. Available from: http://www.acog.org/Patients/FAQs/Premenstrual-Syndrome-PMS
- Mong JA, Cusmano DM. Sex differences in sleep: impact of biological sex and sex steroids. Phil. Trans. R. Soc. B. 2016 Feb 19; 371(1688):20150110.