Obesity–depression associations in the population
Introduction
Obesity and depression are increasingly prevalent and associated with various health complications. Obesity is associated with hypertension, dyslipidemia, diabetes mellitus, coronary heart disease, stroke, as well as increased all-cause mortality [1]. Depression is associated with increased risk of coronary heart disease, myocardial infarction, heart failure in patients with systolic hypertension, low bone mineral density, and increased mortality [2], [3], [4], [5], [6], [7]. Over 60% of the adult US population is overweight or obese [1], and depression is one of the most common psychiatric disorders among patients seeking outpatient care [8]. These disorders incur substantial costs to society [9], [10] and the individual [11], [12].
Obesity and depression research, by and large, have evolved as two independent disciplines. With respect to common etiological models, there have been few developments since early psychodynamic models [13]. With respect to clinical innovations, the two fields rarely overlap. During the past 50 years, it has largely been assumed that relative body weight (RBW: weight adjusted for height) is unrelated to depression in the population. This may be true. However, the relationship may be more complicated than originally believed [14].
This article reviews data on the associations between RBW and depression in the population and summarizes potential moderators and mediators of these covariations. We conclude that there may be multiple covariations and that greater insights will be achieved through increased collaboration between obesity and depression specialists.
Section snippets
Cross-sectional studies
An extensive literature spanning several decades has addressed the relationships among obesity, general psychopathology, and depression in particular [13]. This literature includes community- and clinic-based studies. Results from this literature, on balance, do not suggest a strong or simple relationships among these variables. Most community studies find no significant association [14], [15], some studies reported significantly less anxiety and depression among obese individuals [16], [17],
Identifying moderators and mediators of potential RBW–depression covariations
The mechanisms underlying RBW–depression covariation are largely unknown. However, potential moderators and mediators have been identified in the literature and suggest important avenues for research and clinical intervention. Potential moderators and mediators are summarized in Table 1 and reviewed below. Moderators are defined as variables upon which obesity–depression covariation is conditional. Thus, one may observe an association in one level of a moderator variable but not another (e.g.,
Sociodemographic factors
Demographic variables such as socioeconomic status (SES), income, education, gender, and ethnicity may moderate RBW–depression covariation [14]. The classic “Midtown Manhattan Study” provided perhaps the earliest evidence. In a community study of 1660 New York City residents, the association between obesity and depression significantly varied as a function of gender and SES in persons 20–39 years old (see Fig. 1). Among men, the difference in the percentage of depressed between obese and normal
Negative verbal commentary
History of negative verbal commentary (i.e., weight teasing) is associated with significantly greater depression among obese individuals [50]. In a 3-year prospective study of adolescents, teasing history mediated the relationship between obesity status and subsequent levels of depression [51]. In this model, baseline obesity status elicited teasing, which in turn elicited increased depression 3 years later through increased appearance dissatisfaction (Fig. 5). In a sample of 115 obese females
Conclusions
Fig. 6 pictorially summarizes four generic research models or strategies that have been used to address questions concerning obesity–depression associations. The “bivariate model” tests simple associations between body fat and depression measures, without examining putative moderators and mediators. This strategy has been the most common approach in the literature and, arguably, will yield few new insights by itself at this time. “Moderation models” test whether the relationship between obesity
Acknowledgements
This work was supported in part by NIH Grant No. K08MH01530.
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