A time release composition is provided containing: a chromium complex having formula 3 [Cr.sub.3O(carboxylate).sub.6(ligand).sub.3].sup.+ (3) wherein carboxylate is a C2-C5 alkyl carboxylate and wherein `ligand` is a ligand that (i) renders the chromium complex insoluble or only slightly soluble in water and (ii) is acid labile, being readily displaced under acidic conditions below pH=4 and replaced by water to make the resulting water soluble complex 2 [Cr.sub.3O(carboxylate).sub.6(H.sub.2O).sub.3].sup.+, (2) and the use of the time release composition for the time release delivery of complex 2.