Obesity and mental disorders in the adult general population

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Abstract

Objective

The aim of this study was to investigate (i) the associations between mental disorders (in particular the anxiety disorders) and obesity in the general population and (ii) potential moderators of those associations (ethnicity, age, sex, and education).

Methods

A nationally representative face-to-face household survey was conducted in New Zealand with 12,992 participants 16 years and older, achieving a response rate of 73.3%. Ethnic subgroups (Maori and Pacific peoples) were oversampled. Mental disorders were measured with the Composite International Diagnostic Interview (CIDI 3.0). Height and weight were self-reported. Obesity was defined as a body mass index (BMI) of 30 kg/m2 or greater.

Results

Obesity was significantly associated with any mood disorder (OR 1.23), major depressive disorder (OR 1.27), any anxiety disorder (OR 1.46), and most strongly with some individual anxiety disorders such as post-traumatic stress disorder (PTSD) (OR 2.64). Sociodemographic correlates moderated the association between obesity and mood disorders but were less influential in obesity–anxiety disorder associations. Adjustment for the comorbidity between anxiety and mood disorders made little difference to the relationship between obesity and anxiety disorders (OR 1.36) but rendered the association between obesity and mood disorders insignificant (OR 1.05).

Conclusion

Stronger associations were observed between anxiety disorders and obesity than between mood disorders and obesity; the association between PTSD and obesity is a novel finding. These findings are interpreted in light of research on the role of anxiety in eating pathology, and deserve the further attention of researchers and clinicians.

Introduction

The prevalence of obesity is fast on the rise globally, a trend which began earlier in the industrialized countries of the West [1], [2]. In countries such as Britain, the United States and New Zealand where substantial proportions of the populations are obese, there are far-reaching implications for the current and future burden of chronic disease such as Type II diabetes, cardiovascular disease, certain forms of cancer, and osteoarthritis [1], [3], [4].

While the public health context of the obesity problem is clear, it has been less clear as to whether there is also a mental health dimension to obesity. Obese persons seeking obesity treatment have higher levels of psychopathology, especially binge eating disorders and depression, relative to non-treatment-seeking obese persons [5], [6]. However, evidence on a link between obesity and psychopathology in the general population has been much less reliable, and indeed, some earlier studies suggested that obese persons had better mental health than the nonobese, leading to the “jolly fat” hypothesis [7]. As Friedman and Brownell [8] point out in their extensive review of the earlier research, the variability of findings on this topic is not surprising given the variability in methodologies and measures of mental health, together with the heterogeneity of the obese population and the lack of attention to potential moderators of the relationship between obesity and mental disorders (such as age, sex, socioeconomic status and ethnicity) [8], [9], [10]. Where mental disorders, rather than symptoms, have been investigated, a further limitation is the narrow range of mental disorders included, often confined to major depressive disorder.

There are both cross-sectional and prospective studies reporting associations between obesity and major depressive disorder in older adults [7], [11] and in young adults [12], [13], but relatively few studies have investigated the relationship between diagnosed mental disorders and obesity in general populations spanning a range of ages. Two North American surveys investigating depression found it was associated with obesity in women but not in men [10], [14]. Carpenter et al. [10] additionally looked at ethnicity but found no differences across ethnic subgroups. Neither study looked at age. A German population sample which investigated depression, any anxiety disorder, any somatoform disorder, and any substance use disorder found elevated rates only of any anxiety disorder and only among obese men [15]. In the United States component of the World Mental Health (WMH) Surveys, Simon et al. found significant associations between obesity and lifetime major depression, bipolar disorder, and panic disorder/agoraphobia and that some of these associations were strongest for those with more education and non-Hispanic whites, but they did not find significant sex differences [16]. By contrast, in the New Zealand component of the WMH surveys, sex moderated the relationship between overweight (including obesity) and mental disorders [17], but age and ethnicity were not explored in that study.

In sum, a small number of studies have found a relationship between major depressive disorder and obesity in the general population, and this has frequently been confined to women, while age and ethnicity remain relatively underexplored. But particularly underexplored are the anxiety disorders. As far as we are aware, of the general population studies, those by Simon et al. [16] and Hach et al. [15] are the only ones to include anxiety disorders; Simon et al. investigated only three [generalized anxiety disorder (GAD), panic disorder and agoraphobia], while Hach et al. investigated anxiety disorders as a group, with posttraumatic stress disorder (PTSD), obsessive–compulsive disorder (OCD), and GAD excluded from that group.

There is, therefore, a dearth of information on the relationship between individual anxiety disorders and obesity in the general population. Such an investigation requires a large sample size. The New Zealand Mental Health Survey (NZMHS) [18] is one of the larger of the WMH surveys and one of the few to oversample its ethnic minorities (the indigenous Maori people and Pacific peoples originally emigrating from South Pacific Islands), making it well placed to provide information on the demographic variation in associations between obesity and mood, anxiety, and substance use disorders. The present study therefore uses the NZMHS to investigate the following: (1) Which (if any) mental disorders are associated with obesity in the general population? (2) Are any associations observed moderated by the sociodemographic variables of age, sex, ethnicity, and education?

Section snippets

Sample

Te Rau Hinengaro: the New Zealand Mental Health Survey[18] was a nationally representative household survey involving face-to face interviews with 12,992 people 16 years and older. Interviews were conducted from October 2003 to December 2004 with a response rate of 73.3%. Internal subsampling was used to reduce respondent burden by dividing the interview into two parts. Part 1 included the core diagnostic assessment of mood disorders, alcohol use disorders, most of the anxiety disorders, and

Sample characteristics

Table 1 shows the weighted proportions in each BMI group among the demographic subgroups. Obesity prevalence does not differ meaningfully across males and females, but it is more prevalent among those with less education and among Maori and Pacific ethnic groups, consistent with national health survey estimates using measured height and weight [24].

BMI and mental disorders

The prevalences of any mood disorder, any anxiety disorder, and any substance use disorder in the 11 BMI categories reveal a roughly u-shaped

Discussion

The first question this study aimed to answer was which mental disorders, if any, are associated with obesity in the general population. Previous studies have frequently just focused on depression, so it is interesting that this study found a stronger association between obesity and anxiety disorders rather than mood disorders, and with PTSD in particular. PTSD has not, to our knowledge, been studied previously in connection with obesity in a general population sample. No relationship was

Acknowledgments

Te Rau Hinengaro: the New Zealand Mental Health Survey was funded by the Ministry of Health, the Alcohol Advisory Council of New Zealand and the Health Research Council of New Zealand. Work on this paper was supported in part by the New Zealand Lottery Grants Board. The survey was carried out in conjunction with the World Health Organization WMH Survey Initiative. We thank the WMH staff for assistance with instrumentation, fieldwork, and data analysis. These activities were supported by the US

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