Rainy Day

Cause or Effect? Depression in Obesity

A new study of depression in obesity just published in the British Journal of Psychiatry finds that high BMI likely does not cause depression. The two conditions have long been associated and much speculation about a cause and effect relationship can be found.

In this new study, Chi-Fa Hung and colleagues analyzed data from the 3,222 subject in the case-controlled RADIANT study of major depression.  In their analyses, they factored in data on the FTO SNP genotype and a genetic risk score based on 32 genotypes well-known to be associated with obesity.

As expected, they found an association between obesity and depression. But they conducted two instrumental variable analyses that led them to conclude that excess weight is likely not an important cause of major depression. The association, they concluded, “might be explained by reverse causality and/or residual confounding.”

In other words, it might be that depression causes obesity. Or it might be that some other factor, as yet unknown, explains the link between these conditions.

Clearly this study is not the final word. For an individual, it’s easy to understand how obesity might be a trigger for depression. And it’s easy to understand how depression might lead to eating behaviors that lead to obesity.

But this study makes it hard to support a sweeping conclusion that obesity causes depression.

Find out the cause of this effect,
Or rather say, the cause of this defect,
For this effect defective comes by cause.

— William Shakespeare, Hamlet

Click here to read the study and here to read more about depression and obesity from the Obesity Action Coalition.

Rainy Day, photograph © Nebojsa Mladjenovic / flickr

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