Mendelian randomization investigation highlights different roles of selenium status in mental disorders

Observational studies have suggested a relationship between selenium status and mental disorders (MDs). However, it remains unclear whether selenium status was causally associated with MDs. Thus, we performed a two-sample Mendelian randomization analysis using genome-wide association studies (GWAS) summary statistics to investigate the causal effects of selenium levels on seven MDs, including schizophrenia, major depressive disorder (MDD), autism spectrum disorder (ASD), bipolar disorder (BD), anorexia nervosa (AN), attention-deficit/hyperactivity disorder (ADHD), and panic disorder (PD). Strong genetic instruments of blood selenium (n = 9) and blood-toenail selenium (n = 12) were applied to the above seven MDs GWAS datasets from Psychiatric Genomics Consortium, which were further replicated in the FinnGen Biobank. The inverse-variance weighted method was employed to calculate the causal effects. The results showed that genetically predicted blood selenium levels were associated with a decreased risk of schizophrenia (odds ratio [OR] = 0.90, 95% CI: 0.87-0.95) and AN (OR = 0.87, 95% CI: 0.77-0.97). However, both blood and blood-toenail selenium levels were linked to an increased risk of MDD (blood: OR = 1.08, 95% CI: 1.05-1.12; blood-toenail: OR = 1.08, 95% CI: 1.04-1.13) and ASD (blood: OR = 1.11, 95% CI: 1.05-1.17; blood-toenail: OR = 1.13, 95% CI: 1.05-1.21), respectively. No obvious associations were found between selenium levels and BD as well as ADHD. Our findings highlighted a protective role of selenium in SZ and AN, while a risk effect in MDD and ASD. Further studies are required to verify the underlying mechanism mediating the unequal effects of Se on different MDs, which will pave a new path for the intervention of MDs.