Bipolar Disorder, Schizophrenia, and Metabolic Syndrome

To the Editor: In the March issue, Vancampfort et al. (1) reported valuable data by conducting a meta-analysis of published studies on rates of metabolic syndrome among people with bipolar disorder. In the general findings paragraph, they also compared prevalence of metabolic syndrome among different psychiatric disorders. Rates appeared to be significantly higher in bipolar patients, 37.3% (95% confidence interval [CI]=36.1–39.0), than in schizophrenia patients, 32.5% (95% CI=30.1–35.0) (2). The authors advised caution in interpreting this finding because of the lack of data allowing direct comparison between individuals with schizophrenia and bipolar disorder. However, we believe that this is an important issue that should be more thoroughly assessed and commented on. Among articles screened for suitability for inclusion in meta-analysis, 11 provided data on metabolic syndrome prevalence rates of 3,888 unique participants: 1,572 with bipolar disorder and 2,316 with schizophrenia. Therefore, there may well be sufficient data for a supplementary analysis assessing differences on metabolic syndrome rates between these diagnostic subgroups.

A pooled analysis based on a random-effects model and using odds ratio as an association measure is depicted in Figure 1. The number of individuals with metabolic syndrome was 705 among bipolar patients and 890 among schizophrenia patients. The pooled odds ratio (bipolar compared with schizophrenia) was 1.01 (95% CI=0.82–1.24; p=0.93), with low heterogeneity across the studies (I²=31%; p=0.15). In addition, a subanalysis based on four studies reporting significantly higher rates of antipsychotic prescriptions in people with schizophrenia revealed a similar chance of metabolic syndrome for individuals with bipolar disorder (odds ratio=0.98, 95% CI=0.70–1.38; p=0.91). Further subanalyses did not reveal any statistical difference. We believe these findings may well complement those reported by Vancampfort et al. (1). Individuals with bipolar disorder and schizophrenia have comparable chances of having metabolic syndrome. Despite important differences in clinical features, these individuals may actually share a number of health behaviors, including poor physical activity, unhealthy diet, excessive alcohol intake, and smoking habits. Future research should assess the relative contribution to metabolic syndrome not only of different psychiatric diagnoses, but also of components such as genetics, antipsychotic medication use, lifestyle, and health behaviors.