Relationship between suicide mortality and lithium in drinking water: A systematic review and meta-analysis

Background: : Lithium at therapeutic doses has protective effects against suicide in clinical practice. This meta-analysis aimed to investigate the relationship between lithium concentration in drinking water and suicide mortality in the general population. Methods: : A systematic search was conducted in Web of Knowledge, PubMed, ScienceDirect, and Scopus to find papers reporting the crude relationship between drinking water lithium and suicide incidence in the general population until June 2019. The pooled effect measure was expressed as odds ratio (OR) and 95% confidence interval (CI) using the random-effects model. Results: : We retrieved 308 English original articles, of which 13 ecologic studies with a total sample size of 939 regions and one cohort study with a sample size of 3,740,113 people were eligible for the meta-analysis. A significant relationship was found between the lithium concentration in drinking water and reduced suicide mortality (OR= 0.42; 95% CI: 0.27-0.67; p-value <0.01). Ten studies reported gender-specific responses to lithium, with the pooled estimates as follows: OR= 0.54; 95% CI: 0.35-0.84; p-value <0.01 for men, OR= 0.70; 95% CI: 0.48-1.01; p-value =0.057 for women, and OR= 0.63; 95% CI: 0.47-0.83; p-value <0.01 for total. Limitations: : The study was limited to the assessment of the crude relationship between lithium exposure and suicide rate without considering the role of confounders. Conclusions: : Lithium in drinking water is dose-dependently associated with reduced suicide mortality at least in ecological studies. However, we need well-designed clinical trials to confirm the protective effect of drinking water lithium intake against suicide.