Low risk of male suicide and lithium in drinking water.

OBJECTIVE: Recently, several epidemiologic studies reported that lithium in drinking water may be associated with lower rates of suicide mortality at the population level, but other studies failed to confirm the association. The objective of the present study is to determine whether lithium in drinking water is associated with lower suicide rate after adjustment of potential confounding factors.

METHOD: From 2010 to 2013, 274 mean lithium levels of 434 lithium samples in drinking water were examined in relation to suicide standardized mortality ratios (SMRs) in 274 municipalities of Kyushu Island in Japan. Weighted least squares regression analysis adjusted for the size of each population was used to investigate the association of lithium levels with suicide SMRs. The associations of lithium levels in drinking water with suicide SMRs (total, male, and female) were investigated adjusting for proportion of elderly people, proportion of 1-person households, proportion of people with college education or more, and proportion of people engaging in primary industry (adjusted model 1), and further adjustment was performed with overall unemployment rate, annual marriage rate, annual mean temperature, and annual postal savings per person (adjusted model 2).

RESULTS: Lithium levels in drinking water were significantly (β = -.169, P = .019) and inversely associated with male suicide SMRs but not total or female SMRs in the adjusted model 2.

CONCLUSIONS: The present findings suggest that lithium in drinking water may be associated with the low risk of male suicide in the general population. Further studies are required to confirm these findings and investigate gender differences.