Prevalence of underweight in people with severe mental illness: Systematic review and meta-analysis

People with severe mental illness (SMI) have a higher prevalence of obesity as compared with the general population, however, there is mixed evidence about the prevalence of underweight. Thus, the aim of this study is to determine the pooled prevalence of underweight in people with SMI and its association with socio-demographic factors; and to compare the prevalence of underweight between SMI and the general population. MEDLINE, PsycINFO, and EMBASE databases were searched to identify observational studies assessing the prevalence of underweight in adults with SMI (schizophrenia, major depressive disorder with psychotic features, and bipolar disorders). Screening, data extraction, and risk of bias assessments were performed independently by two co-authors, with disagreements resolved by consensus. Random effect estimates for the pooled prevalence of underweight and the pooled odds of underweight in people with SMI compared with the general population were calculated. Subgroup analyses were conducted for the type of SMI, setting, antipsychotic medication, region of the world, World Bank country income classification, data collection, and sex. Forty estimates from 22 countries were included. The pooled prevalence of underweight in people with SMI was 3.8% (95% confidence interval [CI] = 2.9–5.0). People with SMI were less likely to be underweight than the general population (odds ratio [OR] 0.65; 95% CI = 0.4–1.0). The pooled prevalence of underweight in SMI in South Asia was 7.5% (95% CI = 5.8–14.1) followed by Europe and Central Asia at 5.2% (95% CI = 3.2–8.1) and North America at 1.8% (95% CI = 1.2–2.6). People with SMI have lower odds of being underweight compared to the general population. People with schizophrenia had the highest prevalence of underweight compared to other types of SMI. Japan and South Asia have the highest prevalence of underweight in people with SMI.