Psychological well-being and metabolic syndrome: findings from the midlife in the United States national sample.

Growing research addresses the salubrious health effects of positive psychological functioning, which converges with the World Health Organization's view of health as a state of well-being and more than the absence of disease [1]. Evidence supports independent health benefits of psychological well-being, which is more than the absence of negative psychological functioning, such as depression, anxiety, or anger [2]. Indeed, well-being is a multidimensional domain that has been differentiated into related, but distinct, components. Hedonic well-being typically encompasses constructs such as positive affect, happiness, and life satisfaction. Eudaimonic well-being, in contrast, refers to evaluative judgments about people's lives, such as their sense of purpose and meaning and whether they perceive that personal talents and abilities are being realized [3,4]. Major reviews have synthesized the wealth of evidence linking both hedonic and eudaimonic well-being to optimal health, including in the realm of cardiovascular risk, morbidity, and mortality [5,6]. For example, purpose in life, a key component of eudaimonic well-being, has been found to prospectively predict both reduced risk of myocardial infarction [7] as well as reduced risk of stroke [8], independent of traditional cardiovascular risk factors. This work suggests that well-being predicts lower cardiovascular morbidity and mortality in both healthy and patient populations, independent of health behaviors and traditional risk factors. Identifying links between well-being and reduced cardiovascular morbidity and mortality invites inquiry into the biological processes mediating such associations. Hypothesized mediators include autonomic and neuroendocrine regulation (hypothalamic pituitary adrenal axis and sympathetic nervous system activation), inflammation, and cardiometabolic functioning (e.g., obesity, blood pressure, cholesterol, and glucose regulation). In the current report, we focus on cardiometabolic functioning, assessed via metabolic syndrome, using a large sample of adults across five decades of age. Metabolic syndrome is a constellation of central obesity, hypertension, dysregulated lipids, and insulin resistance or hyperglycemia. Individuals with metabolic syndrome have increased risk for cardiovascular disease, stroke, and type II diabetes [9]. Metabolic syndrome has a high prevalence rate (over 30%) among US adults, with rates increasing in recent years [10]. There are several definitions of metabolic syndrome in the literature, including the National Cholesterol Education Program's Adult Treatment Panel III (ATP III), the World Health Organization, and the International Diabetes Foundation, which vary somewhat in the clinical cut points defining risk [9]. In the current study, our primary outcome was based on ATP III criteria given that this is the definition most commonly used for studies of psychological factors and metabolic syndrome [11]. Although no prior studies have examined links among hedonic or eudaimonic well-being with diagnostic metabolic syndrome, several have documented associations among well-being and individual components comprising metabolic syndrome. For example, HDL cholesterol has been linked with greater optimism in the present sample [12] as well as with greater positive affect, personal growth, and purpose in life in a sample of older women [13]. In the same sample of older women, positive affect further predicted lower levels of glycated hemoglobin over time [14]. Positive emotions were associated with lower rates of hypertension in a sample of older Mexican Americans [15], and happiness was inversely related to ambulatory blood pressure in the Whitehall psychobiology study [16]. A related positive psychological construct, perceived control, was cross-sectionally associated with higher HDL cholesterol and lower glycated hemoglobin and waist circumference in a national sample of middle aged and older Americans [17]. Finally, life satisfaction was inversely associated with excess weight in a community sample of adolescents and young adults [18]. In a recent review, emerging evidence supported associations among well-being and metabolic function, although limited evidence precluded drawing meaningful distinctions among different types of well-being [6]. Findings were also less consistent regarding associations among eudaimonic well-being and glucose regulation and body composition. Few studies have incorporated both hedonic and eudaimonic well-being measures, which is essential to empirically test their comparative effects [cf., 12,18–22]. Although hedonic and eudaimonic well-being measures are moderately correlated, they have previously demonstrated unique associations with central and peripheral health outcomes [4,6,13,23]. The aim of the current study was thus to examine associations between both hedonic and eudaimonic well-being with metabolic syndrome in a national sample of adults known as MIDUS (Midlife in the U.S.). In line with prior evidence, we hypothesized that both types of well-being, although capturing distinct components of positive psychological experience, would be associated with lower risk of metabolic syndrome. That is, both feeling good and being actively engaged in life, may predict reduced risk for cardiometabolic factors implicated in multiple disease outcomes. Our initial analyses focused on cross-sectional associations, but we augment the analyses with longitudinal associations between a subset of well-being assessments, measured 9-10 years earlier, and currently assessed metabolic syndrome.