Girls' diets call for more calcium

Mother Nature's best efforts to protect growing bones come up short when girls' diets contain too little calcium, according to a study at the USDA Children's Nutrition Research Center at Baylor College of Medicine in Houston.

"We know a substantial proportion of adolescent girls have very calcium-poor diets. Yet, little was known about how well their bodies can adapt to minimize the effect of this nutritional challenge," said Dr. Steven Abrams, a BCM professor of pediatrics who studies calcium metabolism at the CNRC, a joint effort with Texas Children's Hospital.

Bone development peaks during puberty, which is why calcium recommendations for children over the age of eight jump to 1,300 milligrams per day, or the equivalent of about four cups of milk, Abrams said. However, dietary surveys suggest that one in five adolescents consumes one-fourth that amount -- or less.

For the study, thirty-six 9- to 13-year-old Caucasian and African-American girls followed either a very-low-calcium or a high-calcium dietary regime for three weeks. The very-low-calcium regime provided one-third the amount of calcium recommended for this age group each day and the high-calcium regime provided the recommended amount. Changes in calcium retention, which is the amount of calcium the girls absorbed from the diets minus natural body losses, was monitored using non-radioactive tracers.

Following a six-week break, the girls switched dietary regimes and repeated the study.

"Since factors such as ethnicity, age, and maturity influence calcium metabolism, the study required that each girl complete both dietary regimes," Abrams said. Once the study was complete, this enabled the researchers to use each individual's high-calcium study results as a baseline, or control, to accurately determine the effect of the very-low-calcium regime on calcium retention.

"Although the girls responded to the low-calcium regime by boosting the percent of calcium they absorbed by nearly 50 percent, their calcium retention was still less than half that achieved on the high-calcium regime," Abrams said.

Because calcium retention determines how much calcium the body can deposit into bones during puberty, the 50 percent shortfall in calcium retention with the very-low-calcium regime is troubling.

The study results are a red flag that strongly suggest that following very-low-calcium diets over a prolonged period of time can put adolescent girls' long-term skeletal health in jeopardy and increase their risk of debilitating bone diseases like osteoporosis.

"Teens and parents need to understand that there are limits to the body's ability to adapt to a diet that is short on calcium or other key nutrients," Abrams said.