Marital status as a predictor of diurnal salivary cortisol levels and slopes in a community sample of healthy adults
Introduction
Married people tend to be healthier than unmarried people (Burman and Margolin, 1992, Kiecolt-Glaser and Newton, 2001). Indeed, compared to those who are married, numerous studies document higher rates of morbidity and mortality among previously (divorced, separated, widowed; e.g., Matthews and Gump, 2002, Carey et al., 2014, Dahl et al., 2015) and never married individuals (e.g., Johnson et al., 2000, Murray, 2000, Idler et al., 2012). Previously married individuals experience increased social isolation (Stafford et al., 2013), a loss of social support (Cohen and Wills, 1985), and stigma related to their separation (Gerstel, 1987). Individuals who are never married also experience stigma and discrimination based on their non-normative marital status (Byrne and Carr, 2005, DePaulo and Morris, 2005, Morris et al., 2007). Recent interpretations of this literature suggest that the health benefits of marriage are partly or wholly attributable to better health in the happily married (e.g., Robles et al., 2014). However, there are reasons that married people might be healthier irrespective of the quality of their relationships such as their access to health insurance, contact with a broader social network, and more regular routines. Either way, this literature suggests that unmarried individuals are subject to experiencing multiple sources of stress that might put them at risk for disease and death.
How might the stress associated with previous marital dissolution or being unmarried impact health? To address this question, it is necessary to consider how stressful experiences may disturb physiological systems (Cohen et al., 2016). One system that is often implicated in models linking stress and disease is the hypothalamic-pituitary-adrenocortical (HPA) axis. The HPA axis produces the hormone cortisol, which plays an important regulatory role for numerous immunological and metabolic processes related to health (Sapolsky et al., 2000). Cortisol levels follow a diurnal pattern, consisting of a rapid rise immediately after waking followed by a decline throughout the afternoon and evening. This rhythm is referred to as the diurnal cortisol slope, and steeper negative cortisol slopes across the day are generally associated with better health outcomes (Adam and Kumari, 2009). Meta-analytic evidence suggests that interpersonal stressors, including experiences of shame or loss, are potent triggers of increased cortisol levels as well as flatter diurnal cortisol slopes (Dickerson and Kemeny, 2004, Miller et al., 2007). In turn, heightened cortisol levels and flatter cortisol slopes are associated with adverse health outcomes such as metabolic syndrome (e.g., Brunner et al., 2002, Anagnostis et al., 2009), coronary atherosclerosis (e.g., Matthews et al., 2006, Dekker et al., 2008), and hastened cancer mortality (e.g., Sephton et al., 2000). As previously discussed, unmarried individuals are more likely to experience ongoing feelings of stigma, social isolation, and discrimination. Insofar as these experiences threaten social well-being, unmarried individuals may be at increased risk for maladaptive changes in cortisol activity as well as for their potential downstream implications for health.
The primary aim of this study was to examine the association between current marital status and daily cortisol levels and slopes. Based on previous literature showing that being currently married is associated with better health and less interpersonal stress, we hypothesized that married individuals would show lower daily cortisol levels and steeper negative cortisol slopes compared to previously married and never married people. We also explored the possibility that lower levels of cortisol among married individuals may stem from their marital status providing protection (stress-buffering) from the consequences of life stress (Cohen and Wills, 1985, Burman and Margolin, 1992, Hostinar et al., 2014). Models of stress buffering contend that close social relationships provide an individual with psychological and material resources that improve coping (Thoits, 1986, Cohen, 2004). To examine this hypothesis, we tested whether perceived stress was associated with less HPA activation among the married than among the previously and never married (perceived stress by marriage status interaction).
To evaluate our hypotheses, we collected multiple measures of salivary cortisol across the waking period of each of three non-consecutive days and compared married, previously married, and never married participants on average area under the curve and steepness of diurnal slopes across the three sampling days. We controlled for demographics, body mass index (BMI), seasons of the year the samples were collected, as well as extraversion, neuroticism, and agreeableness, personality characteristics that may be associated with both selection into marriage as well as cortisol outcomes (Miller et al., 1999).
Section snippets
Participants
We examined archival data combined from three viral-challenge studies. Pittsburgh Cold Study 2 (PCS2) was conducted from 1997 to 2001, Pittsburgh Mind-Body Center Study (PMBC) from 2000 to 2004, and Pittsburgh Cold Study 3 (PCS3) from 2007 to 2011. All three studies were conducted by our laboratory. Full descriptions and data from each study can be found at www.commoncoldproject.com.
In total, 740 participants completed the studies. We excluded those younger than 21 (n = 109) because one of the
Marital status and waking day cortisol levels
Adjusting for the control variables, we found an association between marital status and total levels of cortisol. Specifically, relative to currently married individuals, we found higher cortisol levels among those who were either never married, b = 0.05, p = 0.01, 95% CI = [0.01, 0.09], d = 0.25, or previously married, b = 0.06, p = 0.01, 95% CI = [0.01, 0.10], d = 0.28 (see Fig. 1). These findings were not attenuated by further adjusting the model simultaneously for individual differences in extraversion,
Discussion
Both cross-sectional and prospective studies of the association of marital status and health suggest that married individuals are healthier than either individuals who were never or previously married (divorced, separated, or widowed). These effects are often attributed to higher levels of interpersonal stress experienced by unmarried people. Elevated levels of cortisol, a potential biological consequence of interpersonal stress, is one candidate mechanism accounting for the association of
Role of the funding source
The funding sources had no further role in the writing of this article.
Conflict of interest statement
All authors declare there are no conflicts of interest.
Acknowledgements
Preparation of this paper was supported by a grant from the National Center for Complementary and Integrative Health (AT006694); the conduct of the studies was supported by grants from the National Institute of Mental Health (MH50429), National Heart, Lung, and Blood Institute (HL65111; HL65112), and National Institute for Allergy and Infectious Diseases (R01 AI066367); and secondary support was provided by a grant from the National Institutes of Health to the University of Pittsburgh Medical
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