Lithium is a trace element in human nutrition. Although there are indications of a possible essential function of the alkali metal in the animal kingdom, none has yet been sufficiently defined and proven, thus leaving lithium to be categorized as potentially essential. This work focuses on the impact of dietary lithium on two competitive life-history traits, longevity and fecundity, in the model organism Drosophila melanogaster, with respect to lithiums potential of modulating glycogen synthase kinase-3 (GSK-3) activity.