At least 40% of individuals with alcohol use disorder (AUD) suffer from insomnia, suggesting these issues are highly comorbid (Zhabenko et al., 2012). This comorbidity is due in part to the bidirectional and feed-forward relationship between AUD and insomnia (Koob and Colrain, 2020). Excessive alcohol consumption, including both acute intoxication and withdrawal, negatively impacts sleep. Specifically, acute intoxication leads to more awakenings throughout the night, disruption of REM sleep, and reductions in sleep stages N1 and N2 (MacLean and Cairns, 1982; Williams et al., 1983; Chan et al., 2013). Additionally, alcohol withdrawal leads to insomnia, which can persist for several months following the cessation of drinking (Brower et al., 2011). Specifically, withdrawal is associated with decreases in slow wave sleep, N2 sleep, and REM latency and increases in N1 sleep and REM sleep, and these effects can persist for several months (Williams and Rundell, 1981; Drummond et al., 1998). Conversely, disrupted sleep contributes substantially to alcohol-related problems, in part because alcohol is often used as a sleep aid in an effort to self-medicate sleep disruptions (Johnson et al., 1998; Brower et al., 2001). Given this pronounced interconnection between insomnia and AUD, a better understanding of this relationship could improve intervention and prevention efforts for both disorders.

Associations between alcohol and sleep have historically been assessed in predominately male samples, with women underrepresented in these studies (Baker et al., 2020; Inkelis et al., 2020; Koob and Colrain, 2020). The lack of data on sleep-alcohol associations in women is especially concerning given that both insomnia and AUD are particularly problematic and increasingly prevalent in women. Specifically, women have a higher insomnia risk and self-report greater sleep disturbances and poorer sleep quality than men (Lindberg et al., 1997; Zhang and Wing, 2006; Zhang et al., 2016). Likewise, rates of AUD are increasing much more quickly among women compared to men (Grant et al., 2017). Such high rates of both insomnia and AUD in women highlight the need for studies to directly investigate the reciprocal influence of these disorders in women.

To date, a handful of studies have examined sex differences in associations between poor sleep and alcohol-related problems, and results have been mixed. In some studies, the negative association between sleep and drinking is stronger in men. For example, a large-scale longitudinal study found a bidirectional relationship between heavy drinking and sleeplessness in men, but not women (Rognmo et al., 2019). Additionally, Jaussent et al. (2011) reported that moderate alcohol use was associated with fewer insomnia symptoms in elderly women, whereas no relationship was observed in elderly men. By contrast, other studies have reported findings in the opposite direction, with a stronger negative association between sleep and alcohol use in women. For instance, Haario et al. (2013) found that insomnia was associated with higher rates of heavy drinking and binge drinking in women but not men. Further, in a sample of social alcohol and cannabis users, the association between risky alcohol use and poor sleep quality was stronger in women than men (Ogeil et al., 2015). Taken together, these findings suggest that among heavy drinkers specifically, women may experience stronger associations between alcohol and poor sleep quality than men.

It is important to note that the studies to date examining sex differences in associations between alcohol use and sleep have included predominately healthy, community-dwelling adults with relatively low levels of problem drinking and/or insomnia. Indeed, to our knowledge, no studies to date have examined sex differences in associations between alcohol and sleep in individuals meeting clinical criteria for both insomnia and problematic drinking. Given that alcohol-sleep associations are likely strengthened with increased levels of comorbid AUD and insomnia, this is an important gap in the literature. In order to address this gap, the current study examined sex differences in associations between problematic drinking and poor sleep quality in a sample of heavy drinkers with insomnia. Problem drinking was assessed with the Alcohol Use Disorders Identification Test (AUDIT; Babor et al., 1989) and poor sleep quality was assessed with the Pittsburgh Sleep Quality Index (PSQI; Buysse et al., 1989). We hypothesized that alcohol-related problems would be positively related to sleep disturbances (i.e., individuals with greater alcohol-related problems would also report poorer sleep quality). Moreover, we hypothesized that the association between poor sleep and alcohol problems would be more pronounced in women.

This study examined sex differences in associations between sleep quality and alcohol use in a sample of heavy drinkers with insomnia. Findings showed that poor sleep quality was significantly associated with more alcohol-related problems in women, but not in men. This effect was found even after controlling for several potential confounding variables such as age, global stress, and symptoms of depression. Based on bivariate correlational analyses, the PSQI Sleep Duration and Sleep Disturbances subscales may be driving the observed relationship. In line with previous research (Rice and Van Arsdale, 2010; Tavolacci et al., 2013; Ruisoto et al., 2020), we also found that stress was associated with alcohol-related problems. These findings build on initial studies which have suggested a stronger relationship between sleep and alcohol use in women compared to men (Haario et al., 2013; Ogeil et al., 2015), and help clarify some of the mixed findings from previous reports.

This is the first study, to our knowledge, to test sex differences in the association between poor sleep and alcohol-related problems in a sample of heavy drinkers with insomnia. Prior reports have come primarily from community samples with relatively low rates of problematic drinking, and these studies have typically shown a stronger association between poor sleep and alcohol-related problems in men. The one exception is the study conducted by Ogeil et al. (2015) that tested sex differences in sleep-alcohol associations among social drinkers (i.e., mean AUDIT scores = 8/11 for women/men). This study found that among the riskiest drinkers, sleep and alcohol were more strongly linked in women than men. Our results take this a step further and show that among heavy drinkers at very high risk (i.e., mean AUDIT scores = 17/18 for women/men), the association is especially pronounced in women and non-existent in men. Taken together, these findings suggest that poor sleep is especially likely to accompany heavy drinking in women.

The sex difference in the association between poor sleep and alcohol-related problems observed here lays the groundwork for future studies investigating sex differences in the directionality of this relationship. One hypothesis is that disrupted sleep is more likely to lead to increased alcohol consumption in women than in men. While there is clear evidence from prospective studies to suggest that insomnia and sleep disturbances can play a causal role in the onset of alcohol use and alcohol-related problems (Wong et al., 2004, 2015; Roberts et al., 2008; Hasler et al., 2014, 2016), little is known about sex differences in this relationship. Additionally, a significant number of drinkers report using alcohol to self-medicate insomnia (Johnson et al., 1998; Brower et al., 2001), in which case poorer sleep would lead to greater alcohol use. Although an initial report suggested such self-medication may be more common in men (Johnson et al., 1998), it is possible that this trend may be changing with increasing alcohol use among women. In sum, future studies are needed to determine whether the current findings suggest that poor sleep in women is playing a causal role in increased alcohol consumption.

Alternatively, another hypothesis suggests that greater alcohol use leads to poorer sleep for women than for men (i.e., women may be more sensitive than men to the acute impairing effects of alcohol on sleep). Indeed, one laboratory study (Arnedt et al., 2011) suggests that this is the case. In this study, young adult social drinkers consumed an oral dose of alcohol (target breath alcohol concentration = 100 mg %) 1 h prior to bedtime. Sleep was monitored throughout the night using polysomnography, and results showed that alcohol impaired objective sleep quality indicators to a greater extent in women than in men. Specifically, alcohol decreased total sleep time and sleep efficiency, and increased number of awakenings and minutes awake after sleep onset, in women, but not in men. These findings suggest that our observed association between poor sleep and alcohol use in women may be because heavy drinking causes more pronounced sleep impairment in women.

This study has some limitations. First, there were more women than men in our sample. The observed effect size in men for the relationship between sleep and drinking was quite low, suggesting that the sex difference was not due to greater power in women than in men. However, it will be important to replicate these findings with equal numbers of each sex. Additionally, study measures consisted entirely of self-report measures. Future studies would benefit from inclusion of more objective measures, including actigraphy watches and polysomnography to assess sleep and wrist biosensors to assess alcohol consumption.

In sum, our findings offer important contributions to the literature. Our primary finding, that poor sleep is linked to greater alcohol problems in heavy drinking females (but not males) with insomnia, is particularly novel. These findings further support the hypothesis that sleep quality and alcohol use are linked in women who drink heavily. Future studies are needed to determine the degree to which poor sleep is a sex-specific cause or consequence (or both) of heavy drinking in women. These studies may benefit in focusing specifically on the role of sleep duration and sleep disruptions, since our results point to those two factors as being particularly associated with alcohol problems in women but not in men. This line of research has the potential to contribute important information for the development of sex-specific prevention and treatment efforts for female heavy drinkers, particularly women who suffer from both alcohol-related problems and insomnia.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving human participants were reviewed and approved by University of Kentucky Institutional Review Board. The patients/participants provided their written informed consent to participate in this study.

JW and MM designed the study. JV collected the data, conducted the statistical analyses, and wrote the first draft of the manuscript. All authors revised the manuscript critically for intellectual content and approved the final version.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.