Marital/Cohabitation Status and History in Relation to Sleep in Midlife Women

EPIDEMIOLOGIC RESEARCH HAS SUGGESTED THAT DIVORCED INDIVIDUALS, PARTICULARLY WOMEN, HAVE HIGHER RATES OF SLEEP DISTURBANCE THAN their married counterparts.1–4 Importantly, these studies typically measure marital status at a single point in time, which precludes determination of whether something specific about having a stable partner is beneficial for sleep or whether dissolution of a committed relationship is detrimental for sleep. For example, is the risk attributable to divorce due to the absence of a partner or to the psychosocial sequelae of ending the relationship? Selection bias may also contribute to the effects: healthier people, including those with healthier sleep profiles, may be more likely to enter into and stay in committed relationships. Although directionality cannot be inferred from cross-sectional studies, examination of the association between sleep and the course of relationship status over time, including transitions into or out of committed relationships, provides stronger evidence to support the direction of association linking stable relationships to sleep. The limited extant literature suggests that it is the aftermath of marital dissolution or the affective response of bereavement that is most detrimental for sleep, rather than the absence of the partner per se.5,6 For instance, Reynolds and colleagues6 documented an increased risk for sleep disturbances among bereaved older adults but only among those who were also depressed. Similarly, in a study of the effects of divorce on sleep, Cartwright and Wood demonstrated significant reductions in latency to REM sleep and elevations in the percentage of REM only among divorced individuals who were also depressed.7 As well, participants currently undergoing a divorce had significant reductions in delta sleep (stage 3+4 NREM) compared to those for whom the divorce was finalized.7 In addition, an emerging literature has shown that marital happiness is associated with higher sleep quality in women,8,9 whereas anxiety in close relationships is associated with poorer subjective sleep quality10,11 and indicators of poorer objective sleep, such as percentage of stage 3+4 sleep.12 Taken together, these findings suggest that relationship status per se may be less salient for sleep than are the affective responses to relationship dissolution and/or the underlying qualitative dimensions of high quality relationships, including the degree to which the relationship affords a sense of stability and security. The stability of a marital or cohabiting relationship may be another marker of relationship quality (albeit an imperfect one) that could relate to sleep more strongly than a single, static examination of relationship status. Examining how both relationship status and history contributes to sleep in women is important for several reasons. First, women are more likely to have insomnia than men.13 In particular, midlife is a time of increased risk for sleep disturbances14 and of significant life transitions in women.15 In addition, some evidence suggests that women tend to be more negatively affected, both psychologically and physiologically, by distressed relationships than are men.16 Thus, relationship dissolution may heighten the risk for sleep problems among women by negatively influencing mood and affect and leading to endocrine and autonomic dysregulation, all of which are associated with sleep disturbances, including insomnia.17–20 Sociodemographic factors that have been linked with sleep, including African American race and low socioeconomic status,4,21–23 may also play a role in explaining the sleep benefits of marriage/cohabitation, as unpartnered women are disproportionately represented by African Americans and those in lower socioeconomic strata as compared to partnered women.24 Women who lose a partner due to separation, divorce, or widowhood, often experience a precipitous decline in socioeconomic resources stemming from the loss of the primary or a contributing wage-earner in the family.25 Thus, the stable presence of a partner as well as the gain of a new partner may confer benefits for sleep in women, by increasing a woman's socioeconomic position and access to resources. Given the dynamic nature of marriages and that roughly 40% of marriages end in divorce, with even higher rates among African Americans,26 a critical question that remains unanswered is how relationship history, specifically, the stability of relationship status over time versus changes in relationship status, contributes to sleep quality in women. In addition, the bulk of the extant literature has focused exclusively on marital status as a correlate of subjective sleep outcomes, often assessed using single or few-item measures of sleep with questionable validity and lacking information on normative values.27 Such reliance on subjective sleep outcomes exclusively is particularly problematic given that the unmarried are also disproportionately more likely to be clinically depressed or have elevated depressive symptoms as compared to their married counterparts.28 Thus, observed relationships between marital status and sleep disturbances may be due to general negative affect or reporting bias among the unmarried. Moreover, given the considerable overlap between marital status and other sociodemographic risk factors known to covary with sleep, including race and indicators of SES,4,25 it remains unclear whether marriage is merely a proxy for these known risk factors, or whether having a partner is an independent correlate of better sleep. The current study of sleep, nested in a larger longitudinal study of women's health, examined how marital/cohabitation status (hereafter referred to as marital status) measured concurrently with sleep measures, as well as marital/cohabitation history (hereafter referred to as marital history) assessed over approximately 8 years of study follow-up, were related to sleep in women at midlife. By analyzing marital history over time, we were able to address the question of whether sleep differed according to marital role continuity (consistently married or consistently unmarried over 8 years of study follow-up) as well as marital role transitions, including the gain as well as the loss of a partner. Marital history data was drawn from the longitudinal Study of Women's Health Across the Nation (SWAN), the parent study for the SWAN Sleep Study; a cross-sectional evaluation that involved a multi-modal assessment of sleep, including subjective sleep quality, as measured by the well-validated Pittsburgh Sleep Quality Index (PSQI)29; indices of sleep duration, continuity, and architecture, as measured by multi-night in-home polysomnography (PSG); and behavioral measures of participant's usual sleep duration and continuity, as measured by up to 35 days of actigraphy in participants' usual sleeping environments. Such a multimodal assessment of sleep provided an ideal opportunity to understand whether women's marital status and/or marital history related to well-validated measures of subjective sleep (PSQI) and objective sleep (PSG), as well as their sleep-wake patterns in their habitual sleep environments over an extended period of time (actigraphy). We hypothesized that consistently married/cohabiting women (hereafter referred to as married) would have better sleep, in terms of subjective sleep quality, continuity, and duration as compared to consistently unpartnered women or those who had lost a partner, and that these effects would persist after statistical adjustment for other known risk factors for sleep disturbance. Moreover, consistent with limited evidence linking marital transitions, specifically the loss of a partner due to divorce or widowhood with anomalies in sleep architecture,7,30 we further predicted that women who had lost a partner would have decreased stage 3+4 sleep as compared to consistently married women. We expected that the sleep of women who gained a partner over the course of follow-up would not differ from the consistently married women, as the gain of a partner is generally perceived as a positive life transition31 and also generally positively affects a woman's socioeconomic status.25 Finally, we expected that marital status measured concurrently with sleep assessments would also correlate with sleep outcomes, with the unmarried women having greater sleep disturbances than the married women. However, we expected that sleep differences observed among the married versus unmarried at the univariate level would largely be accounted for by other factors known to covary with both sleep and marital status; specifically, racial and socioeconomic differences between the married and unmarried4 as well as higher rates of depressive symptomatology among the unmarried.28