Background Body mass index (BMI) is correlated negatively with subjective well-being and positively with depressive symptoms. Whether these associations reflect causal effects is unclear.
Methods We examined bidirectional, causal effects between BMI and mental health with Mendelian randomisation using summary-level data from published genome-wide association studies (BMI: n=339 224; subjective well-being: n=204 966; depressive symptoms: n=161 460). Genetic variants robustly related to the exposure variable acted as instrumental variable to estimate causal effects. We combined estimates of individual genetic variants with inverse-variance weighted meta-analysis, weighted median regression and MR-Egger regression.
Results There was evidence for a causal, increasing effect of BMI on depressive symptoms and suggestive evidence for a decreasing effect of BMI on subjective well-being. We found no evidence for causality in the other direction.
Conclusion This study provides support for a higher BMI causing poorer mental health. Further research should corroborate these findings and explore mechanisms underlying this potential causality.
- health behaviour
- mendelian randomisation
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Contributors JLT, KJHV and JMV were responsible for the study concept and the design of the study. NvdB, JLT and KJHV performed the data analyses, under supervision of JMV. NvdB and JLT drafted the manuscript. JKL, MV, KJHV and JMV provided critical revision of the manuscript for important intellectual content. All authors contributed to the interpretation of data and approved the final version for publication.
Funding JMV and JLT were supported by the European Research Council (grant number 284167: ‘Beyond the Genetics of Addiction’, principal investigator JMV). JLT was supported by the Netherlands Organization for Scientific Research (NWO) (Rubicon grant project number 446-16-009).
Competing interests None declared.
Patient consent Not required.
Ethics approval This study made use of publicly available data.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement All data used for this study are publicly available.