Obesity affects the cognitive skills of people with depression, Canadian study finds

Obesity and depression. More detail has been uncovered about the link between them.

A new study from researchers at the Women’s College Hospital in Toronto, the University of Toronto and McMaster University has found that obesity negatively impacts the cognitive skills and functioning of people dealing with a major depressive disorder.

Obesity has become a major health concern in Canada, where the percentage of obese men and women has risen from 15 per cent in 2003 to 20.2 per cent in 2014, according to Statistics Canada. The health risks of obesity are many, ranging from heart disease and stroke to diabetes, some cancers and osteoarthritis, while the direct economic costs of obesity in Canada have been estimated at up to $7 billion a year.

Concerning depression, major depressive disorder (MDD) is expected to become the main cause of disability worldwide by the year 2020. And while the connection between MDD and obesity has been well-established (one study in the United States found that people with MDD have a 21 per cent higher risk of developing obesity than the general population), the precise impact of obesity on those with MDD, particularly with reference to cognitive functioning, is less understood.

To that end, the new study involved three groups of participants, two (obese individuals and obese individuals with MDD) from a list of people who had bariatric surgery for weight loss performed at St. Joseph’s Healthcare in Hamilton and a third group of control participants with body mass indices within the normal range, recruited from the surrounding community. Participants completed a battery of neuropsychological testing looking at memory function, self-control and self-regulation functioning, processing speed and attention.

The results showed a “consistent pattern,” according to the study’s authors, with healthy controls performing better than both groups of bariatric patients across the majority of tests. Further, the bariatric group without MDD outperformed the bariatric MDD group.

“To our knowledge, this is the first study to attempt to examine the potentially deleterious effects of obesity, its comorbidities, and depression on cognitive performance,” say the study’s authors. “When comparing performance patterns across groups, MDD (including both past and current diagnosis) seemed to have an additive negative effect on cognition in the presence of obesity, with comparisons between bariatric MDD and healthy controls resulting in significantly different levels of performance on several cognitive tasks.”

The study’s authors suggest that further research is needed to untangle the interaction between mood disorder diagnosis, obesity and cognitive performance, noting that as obesity appears to add to the cognitive burden for those dealing with preexisting mental health challenges, health care efforts should be focused at reducing the effect of obesity (through weight management programs, for instance) on those with MDD.

An estimated 4.7 per cent of Canadians meet the criteria for major depression. The Centre for Addiction and Mental Health reports that one in five Canadians experiences a mental health or addiction problem in any given year, and only about half of Canadians experiencing a major depressive episode receive “potentially adequate care.”

The study was published in the journal Plos One.