Consuming lots of calcium won't help protect your bones from fractures any more than a moderate amount of the mineral, according to the surprising results of a Swedish study.
"More is not better," said one of the researchers, Karl Michaelsson of Uppsala University.
Scientists have long known that bones lose calcium as people grow older and the risk of suffering from osteoporosis and fractures increases. To safeguard bones, doctors have urged the public - especially older women - to increase their intake of calcium either through dietary sources or supplements.
But there's no agreement about how much calcium is enough. As a result, public health recommendations vary greatly. In Britain, women over 50 are urged to consume 700 milligrams a day; in Scandinavia the level is set at 800 mg; and in the United States and Canada it's 1,200 mg. Australia and New Zealand top the list with 1,300 mg.
Hoping to shed some light on the controversy, Swedish researchers examined data from 61,000 women who were observed for 19 years as part of a mammogram screening trial. Each woman filled out a series of lifestyle and dietary questionnaires that allowed the researchers to estimate calcium intake from food and supplements. A quarter of them had a fracture during the follow-up period.
Over all, the researchers found that women who consumed less than 700 mg of calcium a day had a higher risk of fractures than those who took in larger amounts. But an intake of more than 700 mg per day didn't seem to provide any additional protection, according to the results published in the British Medical Journal.
"As the amount of calcium increases, you would expect the risk of fractures to decrease, but we didn't see that," said the study's lead author, Eva Warensjo, also of Sweden's Uppsala University. "There are no further benefits of increasing your intake beyond 700 mg."
It seems the body can make use of only so much calcium at one time. The excess is excreted rather than absorbed.
Dr. Michaelsson said very few of the Swedish study participants - between 5 and 15 per cent - took calcium supplements. The practice of supplementation, he noted, is far more common in North America.
"If you have a normal diet, you should get sufficient amounts of calcium," he added. "One glass of milk contains 300 mg of calcium - or almost half of what's needed in day. It is not necessary to take supplements." (About 175 ml of plain yogurt and 42 grams of cheese each contain about 300 mg.)
If the Swedish findings are confirmed by further studies, it may help put to rest another simmering controversy regarding calcium. Several recent studies by New Zealand researchers have suggested that taking calcium supplements (but not calcium from food) may increase a woman's chances of developing cardiovascular disease. Indeed, if supplements aren't really required, then concern about potential side effects becomes a moot point.