Bone Gains in New Mothers

Childbearing and nursing do not appear to permanently diminish the density of new mothers’ bones, according to a recent study by scientists at the Children’s Nutrition Research Center at Baylor College of Medicine in Houston. The center is funded by the Agricultural Research Service, the primary science research agency of the U.S. Department of Agriculture.

Led by Judy M. Hopkinson, a lactation physiologist and assistant professor of pediatrics at Baylor, the researchers scrutinized postpartum changes in the bone mass and density of 76 new mothers during a two-year period. Half breast-fed their infants, while half chose to feed formula to theirs. The scientists measured bone densities at regular intervals using a sensitive bone scan called DXA, which can detect small changes in specific bones and bone regions.

Earlier studies suggested that breast-feeding may lead to a loss of bone that could later increase the risk of osteoporosis. In fact, decreases of 4 to 6 percent in lumbar spine bone mineral density (BMD) during lactation have been shown. Nursing mothers lose about 210 milligrams of calcium each day in their breast milk, which can trigger bone loss in areas prone to fractures later in life.

Hopkinson’s study confirmed earlier ones suggesting that new mothers who formula- feed do not experience decreases in bone mass or density. She found bone loss only in breast-feeding mothers. However, she also found that women who breast-fed had complete bone recovery by two years after delivery. Those who breast-fed for nine months or less had nearly 3 percent more bone than right after delivery, while those who nursed up to 24 months also gained bone, but at a slower rate.

Hopkinson believes that this bone loss and recovery cycle allows the nursing mother’s body to repair tiny flaws in her bones, making them stronger than they might otherwise be. She is now monitoring bone densities in women before and after giving birth, to learn more about how pregnancy affects maternal bone formation.

ARS is the U.S. Department of Agriculture's chief scientific research agency.