What biological roles does it play?
There is evidence to suggest that lithium is also an essential plant element (Macrae et al. 1993)
The corresponding associations with the incidence rates of robbery, burglary, and theft were statistically significant withp<0.05. These results suggest that lithium has moderating effects on suicidal and violent criminal behavior at levels that may be encountered in municipal water supplies.
Comparisons of drinking water lithium levels, in the respective Texas counties, with the incidences of arrests for possession of opium, cocaine, and their derivatives (morphine, heroin, and codeine) from 1981–1986 also produced statistically significant inverse associations, whereas no significant or consistent associations were observed with the reported arrest rates for possession of marijuana, driving under the influence of alcohol, and drunkenness.
These results suggest that lithium at low dosage levels has a generally beneficial effect on human behavior, which may be associated with the functions of lithium as a nutritionally-essential trace element. Subject to confirmation by controlled experiments with high-risk populations, increasing the human lithium intakes by supplementation, or the lithiation of drinking water is suggested as a possible means of crime, suicide, and drug-dependency reduction at the individual and community level.
Zarse K., Terao T., Tian J., Iwata N., Ishii N., Ristow M.
European Journal of Nutrition. 50 (5) (pp 387-389), 2011
. Because of lithium's stabilizing effect on glutamate receptors, scientists are also studying whether this medication can protect from the cell death that occurs in conditions such as Parkinson's, Huntington's and Alzheimer's.
Lithium is taken up by all plants, although it appears not to be required for their growth and development. However, this question is not yet completely resolved, since, in the ppb range, stimulatory effects of lithium on plant growth have been observed .