More recently, many calcium supplements have been developed and investigated for a thorough understanding of the mechanism of calcium absorption. The various calcium supplements in the market can be classified into four categories: (i) inorganic calcium salts such as calcium carbonate; (ii) organic acid calcium salts including calcium lactate, calcium acetate and calcium gluconate; (iii) calcium amino acid chelate; (iv) calcium oligo-peptide chelate. In 1960, oligo-peptides were found to transport across the intestinal wall and the absorption rate was higher than that of amino acids (Zhou et al., 2012). Combined with the absorption mechanism of metal ions, calcium oligo-peptide chelate might be absorbed in the pathway of oligo-peptide transport and the bioavailability might be improved.