Using a large, population-based sample from NHANES, we found that, among overweight and obese adults, waist circumference and/or abdominal obesity was significantly associated with increased prevalence and likelihood of having major depressive symptoms or moderate-to-severe depressive symptoms, suggesting abdominal obesity is a strong correlate of depression, particularly for adults who were overweight by their BMI status.
The relationship between depression and waist circumference or abdominal obesity as a component of metabolic syndrome has been explored previously in studies examining the associations of metabolic syndrome with mental illness [39
]. The inconsistent results of these studies may have resulted from differences in the populations being studied, in the measures of depression used, or in the number and type of covariates controlled for across studies. For example, three studies that were conducted in participants aged 35-55 years in London using the 4-item depression subscale of the General Health Questionnaire [39
], in participants aged 25-84 years in Australia using the Hospital Anxiety and Depression Scale [40
], and in Japanese men aged 20-67 years using the Profile of Mood States of the Likert-scale questionnaire [43
] showed a significant association between waist circumference and depression. However, two studies conducted in Finland, one in participants aged 31 years using the Hopkins Symptom Checklist-25 questionnaire [41
] and the other in participants aged 36-55 years using the Beck Depression Inventory [42
], failed to observe a significant association as did studies conducted in Chinese elderly (aged ≥ 55 years) using the Geriatric Depression Scale-15 items [23
] and in participants aged ≥ 25 years in New Zealand using self-reported, physician-diagnosed depression [21
]. Moreover, two studies conducted in middle-aged women (mean age 50.4 years) using the Center for Epidemiological Studies Depression scale [27
] and in overweight premenopausal women using the Zung's Self-Rating Depression Scale [44
] reported that central obesity measured as visceral fat (but not subcutaneous fat) was significantly associated with an increased likelihood of having depression; surprisingly, waist circumference as an indicator of central obesity was not associated with depression in the study conducted by Everson-Rose et al [27
]. A recent study using the PHQ-9 reported that waist circumference in the third and fourth quartiles was significantly associated with an increased likelihood of moderate-to-severe depression but not major depression [45
], however, that study was conducted in U.S. adult women only, and only age- or age- and BMI-adjusted odds ratios were reported [45
]. Our study using the data from both men and nonpregnant women who were overweight and obese further demonstrated that waist circumference and abdominal obesity were significantly associated with both major depressive symptoms and moderate-to-severe depressive symptoms after adjusting for multiple potential confounders. However, we did not conduct sex-stratified analyses because interactions between sex and waist circumference or abdominal obesity on outcome measures were not significant in the present study. In addition, we did not include BMI as a covariate because we only focused on people who were overweight and obese and also because of the high correlation between waist circumference and BMI [46
]. Whether or not BMI should be included as a covariate in studies like ours or in studies dealing with metabolic syndrome [39
] remains controversial at present.
Our stratified analyses by BMI and abdominal obesity revealed that overweight adults with abdominal obesity were more likely to have depressive symptoms (by both definitions) than overweight adults without abdominal obesity; however, there were no differences in obese adults with and without abdominal obesity. The fact that about 96% of obese adults have abdominal obesity may explain this observation. Nevertheless, our finding is consistent with previous research in obese women reported by Ma and Xiao [45
]. Moreira et al.[29
] reported that increasing in waist circumference was significantly associated with an increased prevalence of depressive symptoms and mood disorders in obese women; however, in that study, only simple correlation analysis was conducted and potential confounders were not taken into account. Taken together, the negligible differences in the prevalence and the odds ratios of having depressive symptoms between overweight and obese adults with abdominal obesity in the present study further suggest that waist circumference or abdominal obesity may be a preferred predictor of depression in this population.
Our study is subject to several limitations. First, the causal relationship between waist circumference or abdominal obesity and having depressive symptoms cannot be established based on the nature of our cross-sectional study. A growing body of evidence has shown that a bidirectional relationship may exist. Obesity in adolescence was associated with later depression in young adulthood [22
]. The poor social relationships, low socioeconomic status, and the multiple chronic diseases associated with obesity may have predisposed obese people to impaired mental health. On the other hand, longitudinal studies have shown that baseline depression is a significant predictor of visceral fat accumulation and obesity [48
] and is associated with increased adrenal gland volume [49
]. The latter suggests a long-term increased production of stress hormones from the hypothalamic-pituitary-adrenal (HPA) axis is involved in depression, which contributes to body fat accumulation [51
]. Second, our study was conducted only in overweight and obese participants representing a high risk population; this may have affected the generalizability of our results. Third, we conducted our analyses from combined data from both men and women mainly due to lack of interactions between sex and waist circumference or abdominal obesity on outcome measures and due to relatively small sample size. Future studies using sex-stratified data analyses are warranted to further explore sex disparities in the associations of depression with waist circumference and abdominal obesity and to study the potential effects of menopause on the associations. Fourth, we used PHQ-9 as a measure of depressive symptoms rather than a clinical diagnosis of depression. Although the PHQ-9 depression assessment has been validated in the general population including people who are overweight and obese as well as in patients with diabetes, coronary artery disease, or chronic heart failure, research on specific validation of this instrument in obese adults is currently not available. Thus, studies on clinical diagnosed depression and its association with abdominal obesity are warranted. Finally, antidepressant treatments, which are associated with weight gain [53
], were not taken into account in the present study.