The invention provides, in one aspect, compositions for delivering a bioactive metal ion to a mammal, the compositions comprising (a) an effective amount of a source of the bioactive metal ion, (b) a phosphoprotein preparation obtained by partially cross linking a partial hydrolysate of casein or a caseinate, and (c) one or more physiologically acceptable diluents or carriers. Also provided are compositions for remineralising tooth enamel and/or for treating or preventing dental caries, tooth erosion, dentinal hypersensitivity or gingivitis in a mammal, wherein the compositions comprise an effective amount of such a phosphoprotein preparation, in combination with one or more carriers or diluents. In related aspects, the invention provides methods of using such compositions. Also provided are novel phosphoprotein preparations suitable for use in such compositions and methods.