Orange juice is one of the most convenient fortified products, and companies have been quick to realize its potential for a range of health conditions with the launch of value-added products such as Minute Maid's Heart Wise with cholesterol-lowering plant sterols, and Tropicana Pure Premium Calcium and Vitamin D.
But in the case of calcium, there is not necessarily a correlation between content listed on the nutritional label and actual nutritional value, say researchers at Creighton University, as some forms of the mineral are better absorbed by the body than others.
For their study, 25 healthy premenopausal women consumed one of two commercially marketed calcium-fortified orange juices in an amount providing 500mg of calcium.
One of the juices was fortified with calcium citrate malate and the other with a combination of tricalcium phosphate and calcium lactate.
The participants drank the juice at breakfast time following an overnight fast, and their serum calcium levels were measured over a nine-hour period. Overall, the women who drank the calcium citrate malate fortified product absorbed 48 percent more calcium than the tricalcium phosphate/calcium lactate group.
Lead researcher Dr Robert Heaney has responded to detractors, who say that his findings show that fortified orange juice is inferior to natural sources of calcium.
"While it's great for consumers to get calcium from natural sources like milk, dairy products and dark green vegetables, fortification has proven to be invaluable in supplementing the intake of calcium in the diet," he said.
Although the study used fortified orange juice, the conclusions could bear relevance to other types of fortified foods and supplements too.
Heaney added that he is in favor of manufacturers evaluating absorption of their calcium-fortified products to ensure their effectiveness, and displaying this information on labels to prevent consumers from buying products that do not give them as much nutritional benefit as they think.
This is not the first time that Heaney has carried out research that has questioned the quality of fortified beverages. In another study published in Nutrition Today in February, he concluded that the calcium actually available in some soy and rice drinks can be as much as 85 percent lower than the amount on the product label, owing to the mineral settling at the bottom of the pack.
Calcium is known to help build healthy bones and teeth, and prevent osteoporosis, a brittle bone disease that can affect older women. It is also believed to play a role in the normal clotting of blood, the transmission of nerve impulses, enzyme regulation, insulin secretion and muscle function regulation.
The recommended daily intake of calcium is 1300mg for teenagers, between 1000 to 1200mg for adults and up to 1500mg for postmenopausal women, the group most at risk of osteoporosis.