ReviewThe relationship between abdominal obesity and depression in the general population: A systematic review and meta-analysis
Introduction
It is widely accepted that obesity is strongly correlated with a variety of medical conditions such as cardiovascular diseases, type 2 diabetes and some types of cancer [1], [2], [3]. Two types of obesity are presented among literature, which are general obesity, estimated by the body mass index (BMI); and abdominal obesity, commonly evaluated by waist circumference (WC) or waist hip ratio (WHR). A review article by Shoelson and colleagues suggests that adiposity increases the risk of diseases by promoting a chronic, subacute status of inflammation, for which the adiposity accumulated on the abdomen is particularly a main contributor [4]. By definition, BMI indicates overall fat distribution, thus is not as effective as WC in reflecting abdominal fat [5]. Corresponding to the statement of the role abdominal obesity played in inflammatory pathogenesis, other researchers have observed that BMI combined with WC did not increase the predictive value of health risk compared to WC alone [6], suggesting a greater emphasis needs to be placed on WC [7].
As much the same way as the causal linkage to physical diseases, the mechanism of the relationship between abdominal obesity and depression is associated with inflammatory markers and dysregulation of the hypothalamic–pituitary–adrenocortical (HPA) axis [8], [9]. Impaired feedback regulation of HPA axis is commonly presented in patients with depression [9] and is thought to be responsible for inducing sickness behaviors that are indistinguishable from human major depression (e.g. sleep disturbance, social isolation, feeling down) [10]. At the biological level, dysfunction of HPA feedback regulation is believed to be mediated by a reduced number of glucocorticoid receptors (GR), which result in elevated concentration of cortisol, ultimately interrupting normal regulation [11]. Meanwhile, a decreased level of GR is found to be inhibited by a variety of cytokines [12], [13]. In the immune system, adipose tissue is an endocrine organ that releases cytokines and other molecules, which influence the immune activation by mechanisms stated earlier and eventually lead to, or exacerbate symptoms of depression. Of particular importance to the current research is that abdominal adiposity produces a greater effect on systemic inflammation than other sites of adiposity [4]; therefore, in relation to depression, the role of abdominal fat should be emphasized.
The last decade witnessed an increasing number of studies examining the relationship between obesity and depression among the general population, which is evidenced by emerging publications of systematic reviews for both cross-sectional and prospective relationships of these two constructs [14], [15], [16], [17]. Despite the well detailed description of the relationship between obesity and depression, obesity in these reviews is commonly defined by BMI [14], [15], [16], [17], an indicator of general fat distribution. Given the stronger effect of abdominal fat on the immune system and the greater ability to predict health outcomes, summarizing the relationship between abdominal obesity and depression is clearly a necessity. Meanwhile, although the relationship between abdominal obesity and depression is discussed when reviewing the correlation between metabolic syndrome and depression [18], [19], no systematic review and meta-analysis have been conducted to systematically assess the relationship between abdominal obesity and depression. The purpose of this review is to quantify the relationship between depression and abdominal obesity. Previous systematic reviews for cross-sectional [14] and longitudinal [15] relationships between general obesity and depression have examined the potential moderating effect of gender, age, measurement of depression and study quality indicator. These factors together with the measurement of abdominal obesity have also been examined in subgroup analysis in the study to enable comparison.
Section snippets
Study selection
The search strategy was constructed in consultation with a qualified university librarian, and was considered comprehensive enough to capture all relevant sources of information. Electronic databases were searched for publications up to the end of September 2009. These included PubMed, Cumulative Index to Nursing and Allied Health (CINAHL), PsycINFO, PsychoARTICLE, SPORTDiscus, and ProQuest Psychological Journal. Evidence Based Medicine Reviews Multi-file was also searched including ACP Journal
Results
As shown in Fig. 1, out of the 150 potentially relevant articles selected for further screening, 96 articles were excluded due to no measures of abdominal obesity or depression, use of a clinical population, investigation of weight gain, not available, not relevant to the topic or were commentaries without statistics. The reference lists of the 13 identified review articles were manually searched before exclusion, and no new studies were found. Further, 4 longitudinal studies examining the
Pooled effect size of the relationship between abdominal obesity and depression
Data from the 15 cross-sectional studies using OR as an effect size were meta-analyzed to examine the association between abdominal obesity and depression. Prior to the calculation of pooled effect size, the presence of outliers was examined. The mean OR of studies in this review was 1.49 ± 0.59; therefore, an outlier was any observation beyond the range of −0.28 to 3.26 in the current review. The range of effect size was from 0.75 to 2.86, thus, no outlier was identified based on the above
Discussion
The analysis of 15 cross-sectional studies based on a general population showed a moderate magnitude relationship between abdominal obesity and depression (OR, 1.38; 95% CI, 1.22–1.57), which is stronger than that between general obesity and depression as revealed by the previous study (OR, 1.26) [14]. The observed greater association confirmed the hypothesis of the important role abdominal obesity plays in relation to depression. This finding stresses a clear need to place more emphasis on
Conflict of interest statement
There is no conflict of interest to be declared.
Acknowledgement
Nil.
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