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Marriage, like other close relationships, exerts considerable influence on health. Married people experience lower morbidity and mortality across such diverse health threats as cancer, heart attacks, and surgery. Simply being married, as well has the quality of one’s marriage, has been linked to diverse measures of health. Research has examined the social-cognitive, emotional, behavioral and biological processes involved in these links.

Compared to Other Relationships
Beyond marriage, social relationships more broadly have a powerful impact on health. A meta-analysis of 148 studies found that those with stronger social relationships had a 50% lower risk of all-cause mortality. Conversely, loneliness predicts increased risk for cardiovascular disease, and all-cause mortality. Little work has directly compared the health impacts of marriage compared to those of non-romantic relationships, such as connections with friends or colleagues. However, there are several reasons why marriage may exert a greater health impact than non-cohabiting relationships. Married couples spend time together during a wide variety of activities, such as eating, leisure, housekeeping, child-care and sleep. Spouses also share resources and investments, such as joint finances or home-ownership. Relative to other relationships, the increased interdependence of marriage serves as a source for more intense support and strain.

Romantic couples who live together, but are unmarried may represent a middle ground in health benefits between those who are married, and those who are single. However, people live together without getting married for many different reasons; cohabitation sometimes serves as a prelude to marriage, sometimes not. Selection factors of race, ethnicity and social-economic status predispose certain groups to cohabit unmarried, and these factors also affect the health benefits of marriage and cohabitation.

Measuring Health
Research on the links between marriage and health has measured diverse outcomes. These are broadly categorized as clinical endpoints, and surrogate endpoints, and biological mediators .Clinical endpoints are variables which affect how people feel, function, and survive. They are recognized as important outcomes by health care providers and patients, for instance being hospitalized, or having a heart-attack.

Surrogate endpoints and biological mediators are types of biomarkers—objective indicators of normal or pathological physiological processes. Surrogate endpoints serve to substitute for clinical endpoints. They are expected to predict clinical endpoints, based on scientific evidence. For example, elevated blood pressure has been found to predict cardiovascular disease.

Biological mediators reflect short-term sources of stress which affect health outcomes through repeated or persistent activation. These processes do not have a sufficient evidence base linking them to clinical endpoints in order be elevated to the class of surrogate endpoints. Examples include changes in hormone levels, or immune measures.

Selection and Protection
The health benefits of marriage can be described in terms of selection and protection. People with better health, more resources, and less stress are more likely to marry, and marriage brings resources, and social support. The health benefits of marriage persist even after controlling for selection effects, indicating that being married is protective of health.

Social Support: Two Models
Research on marriage and health is part of the broader study of the benefits of social relationships. Social ties provide people with a sense of identity, purpose, belonging and support. Two main models describe how social support influences physical health.

The main-effects model proposes that social support is good for one’s health, regardless of whether or not one is under stress. The stress-buffering model proposes that social support acts as a buffer against the negative effects of stress occurring outside the relationship ( . Both models have received empirical support, depending on how social support is conceptualized and measured (. Marriage should be a strong source of social support in both models.

Marital Quality
While simply being married is associated on average with better health, the health impacts of marriage are affected by marital quality. High marital quality is typically characterized as high self-reported satisfaction with the relationship, generally positive attitudes toward one’s spouse, and low levels of hostile and negative behavior. Conversely, low marital quality is characterized as low self-reported satisfaction with the relationship, generally negative attitudes toward one’s spouse, and high levels of hostile and negative behavior. A troubled marriage is a significant source of stress, and limits one’s ability to seek support from other relationships. Unmarried people are, on average, happier than those unhappily married. A meta-analysis of 126 studies found that greater marital quality is related to better health, with effect sizes comparable to those of health behaviors such as diet and exercise. Explanations for the links between marital quality and health focus on social-cognitive and emotional processes, health behaviors, and a bidirectional association with mental illness.

Social-Cognitive Processes
People in happy marriages may think about their relationship differently than people in troubled marriages. Unhappily married people often hold their partner responsible for negative behaviors, but attribute positive behavior to other factors —for example, “she came home late because she doesn’t want to spend time with me; she came home early because her boss told her to.” Blaming one’s partner for their negative behavior was associated with prolonged elevations of the stress hormone cortisol after an argument. Spouses in troubled marriages are also likely to misattribute their partners’ communication as criticism. However, the links between these social-cognitive processes and health remain understudied.

Emotional Processes
Emotional processes may also link marital quality and health. People in troubled marriages experience more negative emotions, particularly hostility. Negative emotions have been linked to elevated blood pressure and heart rate, and to increased levels of stress hormones, which may lead to ill health. Emotional disclosure often occurs in well-functioning marriages, and is linked to a host of health benefits, including fewer physician visits and missed work days. However, people in troubled marriages are less skillful in emotional disclosure. Thus, higher levels of negative emotions and less effective emotional disclosure may be involved in linking marital quality and health.

Health Behaviors
Health behaviors such as diet, exercise and substance use, may also affect the interplay of marital quality and health. The health behaviors of married couples converge over time, such that couples who have been married many years have similar behavior. One explanation is that spouses influence or control one another’s health behaviors. A spouse’s positive control techniques, such as modeling a healthy behavior, increase their partner’s intentions to improve health behaviors, whereas negative control techniques, such as inducing fear, do not affect intentions. Marital support may increase the psychological resources—such as self-efficacy, and self-regulation—needed to improve one’s health behaviors.

Mental Illness
Marital problems predict the onset of mental illness, including anxiety, mood, and substance use disorders. Much research has focused on depression, showing a bidirectional connection with marital conflict. Marital distress interacts with existing susceptibility, increasing risk for depression. Conversely, depressive behavior such as excessive reassurance-seeking can be burdensome for one’s spouse, who may respond with criticism or rejection. The links between depression and ill health are well established ; depression is associated with immune system dysregulation, and poor health behaviors, such as lack of exercise, poor sleep and diet, and increased substance abuse.

Biological Pathways
Dysregulation of the cardiovascular, neuroendocrine and immune systems is implicated in the links between marital quality and health.

Cardiovascular Reactivity
Marital conflict, and seeking change from one’s spouse evokes a cardiovascular reaction, increasing heart rate and blood pressure. Couples who are more hostile during arguments have stronger cardiovascular reactions. Heightened cardiovascular reactions are associated with increased risk for cardiovascular disease.

Neuroendocrine System
Hormones produced by the sympathetic-adrenal-medullary axis (SAM) and hypothalamic-pituitary-adrenal axis (HPA) have wide ranging effects across the body. Both axes have been implicated in the links between psychological factors and physical health. SAM activity can be measured by levels of circulating catecholamines—epinephrine and norepinephrine. Negative interactions with one’s spouse have been linked to elevated catecholamine levels, both during and after conflict.

Daily fluctuations in the level of cortisol—a stress hormone—are an important marker of health; flatter slopes of cortisol change throughout the day are strongly associated with cardiovascular disease and related mortality. Lower marital satisfaction has been linked with flatter cortisol slopes across the day, lower waking levels of cortisol , and higher overall cortisol levels. However a meta-analysis found no relationship between marital quality and cortisol slopes.

Immune Pathways
Low marital satisfaction, and hostility during arguments with one’s spouse is associated with increased inflammation. Inflammation part of a healthy response to injury and infection, however chronic and persistent inflammation damages the surrounding tissue. Chronic inflammation is implicated as central mechanism linking psychosocial factors and diseases such as atherosclerosis and cancer Beyond inflammation, lower marital quality is also related to poorer functioning of the adaptive immune system. Marital dissatisfaction and hostility during arguments with one’s spouse are related to poorer ability to control the Epstein-Barr Virus, a latent virus which infects most adults.