Lithium has long been used as a psychotherapeutic drug, and treatment with lithium demonstrably reduces incidence of suicide. Lithium also occurs naturally in groundwater to varying degrees. This study explores the relative amount of Lithium in groundwater and suicide in 18 municipalities in Oita prefecture, Japan over a period running from 2002 to 2006. There are two principle findings:
1) There is a negative correlation between standardized (adjusted) suicide rates and the amount of lithium in the water; and
2) It does not take much lithium to produce this effect.
The study reports that the levels of lithium that seem to have this (as yet replicated) effect are much lower than clinical doses used for stabilizing mood and dealing with more serious psychiatric disorders. This would suggest that lithium has a prophylactic effect that is unrelated to its effects as used in more typical situations, or that long term (life long) exposure produces the observed effect.
Here’s the pretty picture of the data:
Ohgami, H., Terao, T., Shiotsuki, I., Ishii, N., & Iwata, N. (2009). Lithium levels in drinking water and risk of suicide The British Journal of Psychiatry, 194 (5), 464-465 DOI: 10.1192/bjp.bp.108.055798