Obesity, bipolarity may have common mechanisms

By Eleanor McDermid, Senior medwireNews Reporter

The presence of obesity in patients with major depression could be a sign of underlying bipolarity, say researchers.

Giulio Perugi (University of Pisa, Italy) and co-workers found that obese patients were more likely than nonobese patients to have bipolar, rather than unipolar, depression.

In their study of 571 patients having a major depressive episode, 21% had bipolar I or II depression. Overall, 86 patients were obese (body mass index [BMI]≥30 kg/m²), and 31% of these had bipolar disorder, compared with just 19% of the nonobese patients.

The rate of bipolar disorder was even higher among patients with a BMI of 35 kg/m² or above, at 42%, the team reports in the Journal of Affective Disorders.

Obese patients were more likely than nonobese patients to have Hypomania Check List-32 total scores higher than 14 (61 vs 46%), and they had a higher average number of lifetime (hypo)manic symptoms (14.6 vs 12.3).

The researchers say that overlapping symptoms may partly account for the association between bipolar disorder and obesity, explaining that “bipolar depression may include atypical features such as increased appetite, overeating, reduced physical activity and weight gain.”

Obese patients were significantly less educated than nonobese patients, and were more likely to be married. However, having a bipolar disorder diagnosis was a stronger predictor for obesity than was educational level or marital status, increasing the likelihood more than twofold.

Perugi et al say that the obese patients seemed to be well aware of the negative health consequences of obesity, yet were unable to control their food intake “and, in a certain sense, can be considered food addict[s].”

They therefore believe that “[h]ypomanic symptoms and mood instability may represent the background of the impulsive-addictive behaviors frequently observed in bipolar spectrum patients.”

The team suggests that future studies should assess whether obese patients with bipolar depression can control food intake better if treated with mood-stabilizing agents rather than antidepressants.

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