Calcium supplements, once believed harmless insurance against osteoporosis, can actually contribute to poor bone development by blocking the absorption of manganese, a key trace element in bone development.
"There is a manganese absorption problem associated with the use of calcium supplements, especially in large doses," said Constance Kies, Ph.D., who works at the University of Nebraska, Lincoln, and with the Dairy Council of California.
"We did not find the same difficulties with foods containing calcium."
"People think that because of the recent recommendations to increase calcium, they need an extra 1,000 milligrams in supplements in addition to their diet," said Dr. Sheldon Margen, a professor of public health nutrition at the University of California, Berkeley.
Currently, 1,000 milligrams are recommended as the total daily calcium intake. A glass of milk has about 300 milligrams of calcium, and calcium supplements are available in single doses of up to 600 milligrams, the level used in the Nebraska study.
Research from UC San Diego, recently showed manganese, a key trace element in bone development, was deficient in the diets of women with osteoporosis, the bone-thinning disease that affects about 20 million Americans.
Calcium supplements taken with meals also seem to inhibit iron absorption, thereby raising the risk for anemia, according to preliminary research from Tufts University, Boston.
Dr. Bess Dawson-Hughes, principal researcher in the study, said it is unclear whether iron supplements taken between meals block absorption, and a follow-up study to validate preliminary findings was initiated.
Dawson-Hughes recommended that younger women, typically deficient in calcium and iron, be particularly careful using mineral supplements and compensate for any potential imbalances by adjusting their diet.
"I recommend using food sources first to get calcium and manganese because the nutrients are better absorbed when combined with other elements found naturally in the foods," Dawson-Hughes said.
Good sources of calcium are low-fat milk, cheese, yogurt, sardines, salmon, almonds, dark green vegetables and molasses. Manganese is plentiful in brown rice, meat, wheat and rice bran, tea, walnuts and whole grains.