Teenage pregnancy may put girls at risk for osteoporosis

More than one million teenage girls become pregnant each year in the United States, and one-half million of these pregnancies result in live births. In addition to the socio-economic challenges that often accompany early parenthood, pregnant teens face dramatic nutritional demands. A recent study by researchers with the Center for Human Nutrition at the Johns Hopkins Bloomberg School of Public Health was the first to examine the impact of early childbearing on calcium absorption in teens. The study, conducted with a group of teenagers ages 13 to 18 in Baltimore, Md., showed that one-third of these young mothers had a bone mass that meets the definitions of osteoporosis or osteopenia (the precursor condition to osteoporosis) shortly after pregnancy. The study results appear in the December 2003, issue of the American Journal of Clinical Nutrition.

"Adolescents have a narrow window of opportunity to build bone mass and the added demands of pregnancy mean that a mother and her fetus have to compete for calcium," explained Kimberly O'Brien, PhD, principal investigator for the study. "Our study showed that adolescent pregnancy may compromise a girl's ability to reach optimal bone growth and that she may need to consume more calcium than is currently recommended to offset bone loss," added Dr. O'Brien, who is an associate professor with the School's Center for Human Nutrition and Department of International Health.

Dr. O'Brien, who specializes in the study of mineral metabolism in populations with increased nutritional needs, used stable isotope technology to compare rates of calcium absorption during the girls' third trimester of pregnancy and the early post-partum period. Calcium absorption more than doubled in the third trimester, which is comparable to the existing data for pregnant adults. Unlike adult women, however, girls must accrue forty percent of their total bone mass during adolescence.

Girls who consumed more calcium during pregnancy showed less bone loss when tested post-partum than those with poor or average calcium intakes. A related study by this research group also found that a low calcium intake limits fetal bone growth in pregnant teens. Investigators say that more studies are needed to determine the long-term impact of early pregnancy and breastfeeding on a girl's ability to reach peak bone mass. "By characterizing the rates of calcium absorption and bone turnover in adolescent pregnancy, this study was a critical first step towards new recommendations to insure that girls get adequate calcium to prevent or minimize losses and avert any detrimental, long-term effects on bone growth," said Dr. O'Brien.

"Calcium absorption is significantly higher in adolescents during pregnancy than in the early postpartum period" was written by Kimberly O'Brien, Maureen Schulman Nathanson, Jeri Mancini and Frank R. Witter.

Funding for this research study was provided by National Institutes of Health.

News releases from the Johns Hopkins Bloomberg School of Public Health are available at www.jhsph.edu/Press_Room. Information about the Johns Hopkins Center for Human Nutrition is available at www.jhsph.edu/chn/.

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