Soy milk is growing in popularity because of many perceived health benefits by the public of consuming soy. The present study by Heaney et al. in The American Journal of Clinical Nutrition examines the comparative bioavailability of calcium in soy milk when compared to cow's milk, and finds soy milk less calcium-rich at current levels of fortification.
16 healthy men received 300 mg loads of labeled calcium in either soy or cow's milk during a light breakfast. Calcium absorption was evaluated from the concentration of calcium in serum 5 hours after oral dosing. The brand of soy milk tested by the researchers achieved three-quarters of the absorbability of calcium as cow's milk.
The authors recommend that a standard fortification of 500 mg of tricalcium phosphate per serving would result in the same amount of calcium absorbed from a serving of soy milk as would be absorbed from a serving of cow's milk containing 300 mg calcium.
Heaney R P et al. Bioavailability of the calcium in fortified soy imitation milk, with some observations on method. Am J Clin Nut 2000;71:1166-1169.