March 20, 2002 -- Calcium alone can't build strong bones and tissues. New research shows calcium needs phosphorus to maximize its bone-strengthening benefits, and taking a lot of calcium supplements without enough phosphorus could be a waste of money.
Researchers say it's the first time the two elements have been shown to be co-dependent for bone health. Both calcium and phosphorus are found naturally in dairy products, but most calcium supplements and calcium-fortified foods and beverages don't contain phosphorus.
More than half of all bone is made from phosphate, and small amounts are also used in the body to maintain tissues and fluids.
But the study, presented at a meeting of osteoporosis experts, found that taking large amounts of calcium from supplements can interfere with phosphorus absorption.
Women trying to prevent or treat osteoporosis typically take 1,000-1,500 mg of calcium a day in the form of supplements. Researchers found this amount of calcium can bind up to 500 mg of phosphorus -- making it unavailable to the body.
"Although this would present no serious problem for many people, it could impact women over 60 years of age who have diets that contain less than the National Academy of Sciences recommended daily allowance of 700 mg of phosphorus," says study author Robert P. Heaney, MD, of Creighton University, in a news release.
"For these women, the usual calcium supplement, calcium carbonate, may block most of the absorption of phosphorus. If this happens, the calcium won't do much good because bone material consists of both calcium and phosphorus," says Heaney.
Researchers say their study shows both calcium and phosphorus are needed to support any increase in bone mass, and a calcium supplement that contains phosphorus would be preferable to one that provides calcium alone.
Other dietary sources of phosphates include eggs, cereals, and meats.
Rhodia, a major producer of calcium phosphates, partially funded this research.