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Back To Blog > The Relation Between BMI and Psychiatric Disorders

This post is by Monica Velici of Sparta Health

The World Health Organization (WHO) estimated that in 2014, almost 40% of adults were overweight (body mass index [BMI] ≥25 kg/m2) with nearly a third of them being classified as obese (BMI ≥30 kg/m2) (WHO, 2014).

Although the physical comorbidity burden in obesity is well established in literature and among clinicians, its relation to psychiatric disorders is relatively less explored. In the last couple of decades however, evidence has been slowly accumulating relating to the link between various psychiatric disorders and BMI, particularly among those seeking treatment for the same. Despite this, knowledge gaps exist about the strength and the direction of the association between obesity and various psychiatric conditions.

Genetics studies have found an association between BMI and psychiatric disorders such as schizophrenia, bipolar disorder and major depression. According to a genome-wide association study, published in JAMA Psychiatry journal there is evidence for overlapping genetic risk variants between BMI and major psychiatric disorders.

According to Ole A. Andreassen, MD, PhD, of the Institute of Clinical Medicine at the University of Oslo in Norway, individuals with major depression and bipolar disorder have an increased genetic risk for a larger BMI. This, together with lifestyle, dietary options, and medication account for the increased weight that many individuals experience. On the other hand, in schizophrenia, the increased BMI can be explained by lifestyle and medication alone, as opposed to an increased genetic risk. In fact, individuals with schizophrenia have been found to be slimmer compared with those with major depression and bipolar disorder. 

Andreassen and colleagues argued that genetic studies have highlighted a relationship between BMI and major psychiatric disorders, with increased weight associated with treatment response across the three psychiatric disorders: bipolar disorder, major depression, and schizophrenia. To determine the extent of the overlap between BMI and these psychiatric disorders, as well as to identify the genes shared between them, the researchers analysed data from genome-wide association studies. Data was available for 1,380,284 participants. Specifically, they focused on statistics such as BMI, schizophrenia, bipolar disorder, and major depression using a conditional false discovery rate statistical framework. This framework increases power of discovery, so in other words, it can accurately identify the shared genetic risk factors between increased BMI and psychiatric disorders. 

Researchers found that the genetic correlation – or the connection between BMI and major psychiatric disorders varied. BMI shared 63 genes with schizophrenia, 17 genes with bipolar disorder, and 32 genes with major depression. Essentially, these findings mean that the same genes responsible for schizophrenia, bipolar disorder, and major depression also account for increased BMI.

According to statistical analyses, the overlapping genes are involved in several pathways including intracellular processes, neurotransmitter signalling and neurodevelopment. The intracellular processes are responsible for the wake-sleep circle – such as, sleeping at night and being awake during the day. Neurotransmitter signalling facilitates the communication between brain and body areas, for example it transmits signals from one neuron to another “target” neuron and then to a muscle. Neurodevelopment refers to the brain's development of neurological pathways that influence performance or functioning (e.g., intellectual functioning, reading ability, social skills, memory, attention or focus skills).

According to Andreassen, these findings provide new insights into the relationship between brain and body by showing an unexpected high number of overlapping genetic risk factors. Firstly, these results demonstrate that mind and body are interrelated, being able to shape the basis for future experimental studies identifying the functional mechanisms involved. Secondly, surprisingly schizophrenia risk variants mainly protected against increased BMI, while the opposite effects were observed for major depression and bipolar disorder.  

About Monica Velici

Monica joined Sparta Health in February 2020 as part of the rehabilitation service support team. She has a degree in Psychology, an MSc in Clinical Neurodevelopmental Sciences, and a keen interest in dementia and mental health. Monica aims to become a fully accredited therapist.


Andreassen, O. A., Bahrami, S., Steen, N. E., Shadrin, A. et al., (2020). Shared Genetic Loci Between Body Mass Index and Major Psychiatric Disorders: A Genome-wide Association Study. Jama Psychiatry. 77(5): 503 – 512. doi:10.1001/jamapsychiatry.2019.4188

World Health Organization. World Health Statistics 2014. Geneva: World Health Organization; 2014. [Last cited on 2016 Nov 20]. Available from: . [Google Scholar]


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