The physical state of calcium fortification of 14 calcium-fortified beverages available to consumers was evaluated and compared with unfortified, fat-free milk. Fortification was evaluated by extrinsic labeling of each beverage with a calcium isotope, followed by equilibration in the refrigerator for 17 hours, and then by centrifugation and separation of the calcium into solid and soluble moieties. Exchangeability of the 2 physical components was evaluated by measuring how well the isotope partitioned between the calcium in the 2 phases. The cow milk referent had 11% of its total calcium separable by centrifugation, but that calcium had achieved 91% of the tracer level predicted for its calcium content, indicating a high degree of exchangeability. All of the soy and rice beverages had most of their calcium in a separable, particulate form, in amounts ranging from 82% to 89% of the total calcium of the beverage. The orange juices had lesser amounts of their calcium separable by centrifugation (range: 8.1%-50.4%). Tracer equilibration of the particulate calcium ranged from a low of 17% of predicted to a high of 85% for the orange juices, and from 25% to 79% for the soy and rice beverages. Two of the orange juices had profiles comparable to cow milk, but most of the remainder fell between the extremes of cow milk and the milk substitute soy beverages. An earlier study had shown that poorly exchangeable, particulate calcium in a fortified beverage exhibited reduced bioavailability in human tests. Many of the beverages tested in this study exhibited similar physical characteristics, suggesting that their bioavailability would be compromised as well. We conclude that the quality of calcium fortification in currently available beverages is uneven at best, with the result that consumers are likely to be misled with respect to the calcium benefit the beverage is presumed to confer. The beverage industry should establish standards that would ensure a uniform, high quality of calcium fortification.
Its important to consider bioavailability
Robert P. Heaney obtained his MD from Creighton University and his research training at the Oklahoma Medical Research Foundation and the National Institutes of Health, Bethesda, Md. He is currently holder of the all-University, John A. Creighton Chair at Creighton University in Omaha, Neb. His research focuses on bone biology, calcium nutrition, and vitamin D.
Karen Rafferty is a registered dietitian and licensed medical nutrition therapist. She is the senior research dietitian with the Osteoporosis Research Center, with a primary focus on calcium nutrition throughout the lifecycle.
June Bierman, BS, MT (ASCP), is the chief laboratory technician in the Osteoporosis Research Center biochemistry laboratory.
Corresponding author: Robert P. Heaney, MD, Creighton University, 601 N30th St, Suite 4841, Omaha, NE 68131 (e-mail: firstname.lastname@example.org).