Sleep as a mechanism through which social relationships affect health.

In this issue of SLEEP, Troxel and colleagues1 offer an original inquiry into the interconnections between enduring social relationships and sleep, inviting clinical and scientific readers to recognize sleep as embedded within the social world. These links between sleep and one's social experience encompass a wide range of overlapping sociodemographic and psychosocial factors including social relationships, as discussed here, in addition to race/ethnicity, culture, employment, education, workplace environment, and neighborhood context.2–6 In combination with the emerging literature on the social determinants of sleep, the work of Troxel and colleagues1 reflects the welcome addition of a social dimension in the way we study the complicated phenomenon of sleep. The late social epidemiologist Geoffrey Rose argued that “the primary determinants of disease are mainly economic and social, and therefore its remedies must also be economic and social.”7 Applying Rose's social epidemiological perspective to understanding sleep, as Troxel et al.1 do, offers a significant advance in the field of sleep research and will lead to better prevention, diagnosis, and treatment of sleep disorders. In their article, Troxel and colleagues1 investigate data from the longitudinal Study of Women's Health Across the Nation (SWAN) on sleep quality in a multi-ethnic menopausal female population. Building on prior work that identifies relationship quality and happiness as independent predictors of good sleep,8,9 the authors seek to understand the associations between relationship history (as an improvement on the crude cross-sectional measure of relationship status) and a range of objective and subjective sleep outcomes. They find that a stable relationship history over the preceding 8 years is associated with better sleep quality and continuity, even after adjustment for a range of social and behavioral factors. Specifically, multivariate regression analyses show that consistently partnered women over the preceding 8 years had fewer sleep complaints than those who had lost a partner during that time. In addition, they indicate that consistently partnered women had lower actigraphy-assessed wakefulness after sleep onset and sleep fragmentation than two groups of women—those who were consistently unmarried and those who had gained a partner. While this research does not prove causality, the findings suggest that having an enduring relationship has meaningful positive implications for sleep. The next critical steps involve identifying what mechanisms are underlying this relationship, whether they are physiological, psychological, behavioral, or socioeconomic. For example, lasting relationships may benefit sleep through hormonal and psychological responses to emotional intimacy, more regular sexual activity, and increased social support. Relationships may also affect sleep through improved health behaviors (fewer drugs, less binge drinking), more routine schedules, and greater financial security. This investigation1 fits into a larger area of inquiry about the positive associations between marriage and health. Social scientists have puzzled over the widely observed finding that marriage appears to confer a health benefit unto its participants. That is, statistically, married people are healthier and live longer than singles (including never marrieds, widows, and divorcees).10 Explanations addressing the underlying mechanisms for this association tend to focus on socioeconomic, psychological, and behavioral reasons (e.g., married people tend to have more household income, better psychosocial support, and improved health behaviors). Surprisingly, the marriage-health literature has generally failed to identify intermediate physiological mechanisms that explain why the presence of a romantic or life partner may improve one's health. Troxel's current and previous work1,8,9 investigate sleep as a plausible physiological mechanism to better understand the “marriage advantage” in health. The idea that sleep is part of a causal process through which social experiences translate into health outcomes has only rarely been investigated in the social determinants of health literature.11,12 Continued efforts such as this work by Troxel and colleagues1 will help identify the likely role of sleep as a mechanism through which social differences in health emerge. Future research should first seek to replicate these findings in various subpopulations (e.g., men and women, old and young) with longer relationship histories than used in this study. Further, there is an essential challenge to better address concerns about marital selection and unobserved confounding factors. Both the marriage-health literature and the much smaller body of marriage-sleep literature are vulnerable to criticism for neglecting to account fully for the strong selection factors of married couples. That is, healthier people are more likely to marry because some of the same characteristics that are beneficial to both health and sleep are also successful on the marriage market (e.g., well-educated, employed, healthy weight).3,13 In this particular study,1 the more relevant question may be whether there is selection out of marriage. Rather than conceiving of the causal direction in the observed associations as going from enduring relationship to better sleep, is there a possibility that better sleep makes relationships stronger? Does difficulty sleeping adversely affect relationship stability? Indeed, limited evidence suggests that the presence of a sleep disorder, such as sleep apnea, adversely affects the sleep and relationship functioning of both partners, while successful treatment of OSA can ameliorate relationship distress.14–16 Further confounding factors (e.g., a death of a loved one, depression, or severe illness) could also be simultaneously affecting both sleep and marital happiness. Given the fact that marital partners are not randomly assigned, identifying the causal direction of these relationships presents methodological challenges. Troxel and colleagues1 offer additional support for the notion that the underlying causes of sleep disorders are socially determined, and are part of a causal chain between social experience and health. This idea that sleep is a mechanism through which social factors affect health considerably broadens the scope of sleep research to include social, environmental, policy and cultural factors. Studying sleep through a social epidemiological perspective may create opportunities to design treatments, policies, and interventions that may simultaneously improve population sleep and health.