Bromine is essential for animals
McCall and colleagues showed bromide is a required cofactor for forming sulfilimine cross-links in collagen IV of basement membranes; bromine-deficient fruit flies died and adding bromine back restored viability, making bromine an essential trace element for animals.
As reported in: McCall, Cummings, Bhave et al. (2014). Bromine Is an Essential Trace Element for Assembly of Collagen IV Scaffolds in Tissue Development and Architecture. Cell. doi:10.1016/j.cell.2014.05.009