In a study carried out by Purdue University and published in the Journal of Clinical Endocrinology and Metabolism (April), researchers discovered that Caucasian girls lose more calcium in their urine than African-American girls, but both races lose calcium at an accelerated rate when they consume a high-salt diet.
"While we found a racial difference in calcium retention in adolescents, we also confirmed that blacks retain more sodium on a high-salt diet than whites," said Connie Weaver, head of Purdue's department of foods and nutrition. "This proves that salt is processed differently in the races, but too much salt in the diet reduces bone density in both races."
She explained that sodium causes water retention, which leads to high blood pressure - a condition that could be related to the high prevalence of hypertension in adult blacks.
"So even though salt intake is less critical to blacks with respect to building bones, we still have to be concerned about how sodium affects heart health," she said.
The results were based on figures from Purdue's 'Camp Calcium' - a summer camp, funded by the National Institutes of Health, that is designed to investigate various aspects of calcium metabolism in adolescent girls and boys.
Thirty-five campers were selected to participate in two, 20-day summer camps separated by two weeks. During the trial, the girls ate a controlled diet that provided certain amounts of calcium and other nutrients under 24-hour supervision.
The participants included 22 African-American girls and 13 Caucasian girls between the ages of 10 and 15. Berdine Martin, research associate and Camp Calcium project director, said the age range was important because calcium absorption is highest just after a girl's first menstrual cycle.
During the first session, half of the girls received a low-sodium diet and half received a high-sodium diet. The diet was reversed during the second session.
The researchers found that adolescent girls need to have the equivalent of four cups of milk a day to take full advantage of the time when their bodies can develop peak bone mass.
Moreover, they keep 25 per cent of the net calcium they consume, but by the time they are young women, it drops to 5 percent.
"Salt intake affects how the body uses calcium at a critical time of bone development in young girls, but in whites more than in blacks," said Weaver. "This is something that should be easy to monitor in order not only to ensure healthy bones in adults, but also to reduce health-care costs of our aging populations."
Weaver admitted that a longer study could reaveal more information, but thought it would be difficult to control diets so strictly.
However, the camp will be continue its research, this time looking at Asian adolescents.