Obesity and common mental disorders, such as anxiety and depression, independently account for a substantial proportion of the global burden of disease and its associated economic costs, so it is important to determine the interaction between the two conditions. In the linked prospective cohort study (British Whitehall Study II; doi:10.1136/bmj.b3765), Kivimäki and colleagues looked for a bidirectional association between obesity and common mental disorders.1 Between 1985 and 1988, they recruited civil servants who were aged 35-55 years at baseline and studied them in three waves over 19 years. They found that common mental disorders were associated with an increased risk of obesity, and that the risk of obesity increased with the number of episodes of depression or anxiety. In contrast, they found weaker non-significant associations between obesity and the risk of common mental disorders.

Kivimäki and colleagues’ findings are consistent with previous cohort studies showing that baseline depression or anxiety predict obesity,2 3 4 but …