The words "ADDED CALCIUM" are splashed on the labels of many food products, from bread to orange juice to soft drinks. But all that added calcium may not provide much health benefit -- in fact, it may cause some harm.
"Manufacturers will put in whatever amount of nutrients will help sell their product," said Lora Sporny, a professor of nutrition at Columbia University in New York. "But we have to recognize that there's a downside to all this calcium supplementation."
Calcium is an important nutrient, aiding the body in bone development, nerve function, muscle contraction, and blood clotting. In addition to its role in preventing osteoporosis, calcium may also help prevent PMS.
Most dietary experts agree that 1,000 mg of calcium daily is sufficient for healthy individuals under the age of 50. Over the age of 50, 1,200 mg per day is recommended.
"The real problem with calcium," said Sporny, "is that when too much gets dumped into your digestive tract, it affects absorption of other nutrients. The two most important nutrients are iron and zinc."
Ironically, those women who are most conscientious about their diets may be the ones most at risk. Because calcium blocks absorption of iron and zinc, women who have diets high in calcium are often deficient in these two important minerals.
"Women of childbearing age need enough calcium for bone mineralization," Sporny said. But if these women over-fortify their diets with calcium supplements, "day after day they become iron deficient."
Calcium intake is also an issue for the elderly.
"Calcium use has been shown to cause zinc deficiencies in elderly people," said Dr. Sattar Hadi, assistant professor of medicine at Vanderbilt University's Center for Human Nutrition in Nashville, Tenn. "That needs to be studied more thoroughly."
The easy availability of over-the-counter supplements is another issue. "A lot of time, patients don't get the information they need for taking these OTC supplements, and may not know how they interact with one another," Hadi said.
Sporny points to breakfast as a good example of a meal where calcium over-fortification is a risk, since many popular breakfast foods have added calcium.
"Total cereal has 100 percent of the recommended daily allowance of calcium," she said. But one serving of that cereal is just three-quarters of a cup, "and women may be eating two to three servings."
When calcium-rich milk is poured over that cereal, and a glass of calcium-fortified orange juice is served, a woman may be getting several days' worth of calcium at one breakfast. "All that calcium can cause iron absorption to drop 30 [percent] to 50 percent," Sporny said.
So how do women know how much calcium is enough?
There is no one-size-fits-all answer, though staying near the recommended daily allowances should be sufficient for most women. "It's hard to make a blanket statement when so many women are not getting enough calcium. The key is striking the right balance," Sporny said.
"We've evolved as a species with nutrients found in food, where nutrients are presented in very small doses," she said. "Anything like iron and calcium are best absorbed when presented to the digestive tract in smaller doses throughout the day."