Obesity comorbidity in unipolar major depressive disorder: refining the core phenotype

While a significant body of research has demonstrated high comorbidity rates between depression and obesity, the vast majority of this work has considered depression as a unitary diagnosis. Given that increased appetite and weight gain are highly characteristic of the "atypical" subtype of depression, while classic depression is characterized by decreased appetite and weight loss, it would be important to examine whether increased obesity risk is consistent across the major vegetative subtypes of depression or is limited to the atypical subtype.

Using data from the 2001-2002 National Epidemiologic Survey on Alcohol and Related Conditions (NESARC), we identified 5,092 US adults with past or current major depression based on DSM-IV-TR criteria and 1,500 gender-matched controls. Each depressed subject was designated as having classic, atypical, or undifferentiated depression based on core vegetative symptoms. Logistic regression models examined rates of current obesity (defined as a current body mass index [kg/m2] > 30) across the 3 depressive subgroups and nondepressed controls, adjusting for demographic differences. To limit the possible effect of current depressive symptoms on observed obesity rates, secondary analyses were completed in individuals with past depression only.

Subjects with atypical depression had markedly elevated obesity rates compared to population controls and to other depressed subjects, with corresponding pairwise odds ratios consistently greater than 2.0 (P < .001). In contrast, obesity rates were not significantly different in subjects with classic depression and nondepressed controls. These results were manifest in individuals with either current or past depression and were independent of gender and age.

While many individuals with classic depression will present with obesity due to the high prevalence of both disorders, only atypical depression is associated with an elevated risk of obesity relative to the population at large. Refining the target phenotype(s) for future work on depression and obesity might improve our understanding, prevention, and treatment of this complex clinical problem.