Obesity is highly prevalent and disabling, especially in individuals with severe mental illness including bipolar disorders (BD). The brain is a target organ for both obesity and BD. Yet, we do not understand how cortical brain alterations in BD and obesity interact.

We obtained body mass index (BMI) and MRI-derived regional cortical thickness, surface area from 1231 BD and 1601 control individuals from 13 countries within the ENIGMA-BD Working Group. We jointly modeled the statistical effects of BD and BMI on brain structure using mixed effects and tested for interaction and mediation. We also investigated the impact of medications on the BMI-related associations.

BMI and BD additively impacted the structure of many of the same brain regions. Both BMI and BD were negatively associated with cortical thickness, but not surface area. In most regions the number of jointly used psychiatric medication classes remained associated with lower cortical thickness when controlling for BMI. In a single region, fusiform gyrus, about a third of the negative association between number of jointly used psychiatric medications and cortical thickness was mediated by association between the number of medications and higher BMI.

We confirmed consistent associations between higher BMI and lower cortical thickness, but not surface area, across the cerebral mantle, in regions which were also associated with BD. Higher BMI in people with BD indicated more pronounced brain alterations. BMI is important for understanding the neuroanatomical changes in BD and the effects of psychiatric medications on the brain.

Common mental disorders (CMD) cause large suffering and high societal costs. Cognitive behavioural therapy (CBT) can effectively treat CMD, but access to treatment is insufficient. Guided self-help (GSH) CBT, has shown effects comparable with face-to-face CBT. However, not all patients respond to GSH, and stepping up non-responders to face-to-face CBT, could yield larger response rates. The aim was to test a stepped care model for CMD in primary care by first evaluating the effects of GSH-CBT and secondly, for non-responders, evaluating the additional effect of face-to-face CBT.

Consecutive patients (N = 396) with a principal disorder of depression, anxiety, insomnia, adjustment or exhaustion disorder were included. In Step I, all patients received GSH-CBT. In Step II, non-responders were randomized to face-to-face CBT or continued GSH. The primary outcome was remission status, defined as a score below a pre-established cutoff on a validated disorder-specific scale.

After GSH-CBT in Step I, 40% of patients were in remission. After Step II, 39% of patients following face-to-face CBT were in remission compared with 19% of patients after continued GSH (p = 0.004). Using this stepped care model required less than six therapy sessions per patient and led to an overall remission rate of 63%.

Stepped care can be effective and resource-efficient to treat CMD in primary care, leading to high remission rates with limited therapist resources. Face-to-face CBT speeded up recovery compared with continued GSH. At follow-ups after 6 and 12 months, remission rates were similar in the two groups.