Obesity may aggravate bipolar neuropathology

By Eleanor McDermid, Senior medwireNews Reporter

Being overweight may result in increased white matter loss in key brain regions in patients with bipolar disorder, research suggests.

“Our results… immediately suggest a neurobiological mechanism to explain the link between obesity and poor psychiatric outcomes in [bipolar disorder],” say Lakshmi Yatham (University of British Columbia, Vancouver, Canada) and colleagues.

The findings “are all the more remarkable considering the weight distributions of our participants,” they add, in Biological Psychiatry.

The average body mass index (BMI) of the 57 patients in the study was normal, at 24.1 kg/m²; just 26% were overweight, and 9% were obese. The 55 mentally healthy control participants had a similar weight distribution.

In the patients, increased BMI was significantly associated with reduced white matter volume in a large area covering the right frontal and temporal lobes and a number of subcortical areas. There was also a smaller area of reduced white matter that included the left temporal lobe and subcortical areas.

In addition, elevated BMI was associated with reduced gray matter volume in the right superior, middle, and inferior temporal gyri and uncus. For all three areas, BMI was a stronger predictor of reduced tissue volume than were age, gender, or use of mood stabilizing medication.

“There is little doubt that the weight-related volume reductions in our patients were in brain areas relevant to [bipolar disorder],” say Yatham et al.

For example, they say that the gray matter reduction associated with BMI occurred in an area known to be involved in emotional processing, and the white matter reductions involved areas identified as abnormal in a meta-analysis of imaging studies in bipolar disorder patients.

In controls, by contrast, elevated BMI was associated only with reduced gray matter volume in the occipital lobes.

The researchers caution that the cross-sectional study design cannot establish causality, but say: “Nonetheless, our results have implications for understanding neuroprogression and the neuroinflammatory hypothesis of mood disorders and create a compelling argument for examining the neurobiological impact of obesity in other mental illnesses with high obesity rates, such as major depressive disorder and schizophrenia.”

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