Newswise — South Dakota State University research shows that a child with leaner body mass, or muscle, builds bigger bones than a child who weighs the same but has a greater percentage of fat. "We were interested in the relative influence of lean mass, which is muscle, versus fat mass on how bone grows as kids grow," said Howard Wey, an associate professor in SDSU's College of Nursing. Wey and professor Bonny Specker, director and chair of the Ethel Austin Martin Program in Human Nutrition at SDSU, are continuing to study the issue. They have analyzed data Specker and her team have assembled by taking bone and body composition measurements of rural Hutterite children in South Dakota. "There's a little bit of controversy because weight itself has a positive influence on bone," said Wey. "Heavier individuals tend to have more bone just to support their weight." The SDSU study was designed to look deeper at that issue to see whether there are differences in how lean mass and fat mass correlate with bone development. Wey presented the findings at the annual meeting of the Pediatric Academic Societies in Baltimore in early May. "A larger child is going to have larger bones just because he's heavier," Wey said. "But if you have two kids at the same weight, the one whose weight is dominated by fat mass is more likely to have smaller bones than the one whose weight is dominated by lean mass. Smaller bones are weaker than larger bones." The study is an offshoot of SDSU's ongoing South Dakota Rural Bone Health Study, directed by Specker. To date the project has tracked more than 1,700 individuals over a three-year period to evaluate how lifestyle affects bone density in three groups of people: Hutterites, rural non-Hutterites and non-rural non-Hutterites.

The National Institutes of Health funds that research. The Ethel Austin Martin Endowed Program in Human Nutrition also supports SDSU's ongoing bone research. To study fat mass versus lean mass as a factor in bone development, the SDSU researchers gathered two to three measurements over a 36-month period on about 150 male and about 200 female Hutterite children ages 8 to 18. Because they are growing children, all the children in the study showed increases in bone mass, area and density, Wey noted. But there were clear differences in rates of change. "We looked at multiple measurements over time. We found that lean mass had a positive effect on rates of change," Wey said. "Kids with higher lean mass, or muscle, tended to have greater rates of change, and kids with higher fat mass tended to have lower rates of change." Wey said the results are preliminary but are fairly consistent. They also confirm what Specker's research team has learned in a cross-sectional study of Hutterite children. That study — essentially a look at an entire group of children at one point in time — suggests that lean mass has a positive effect on bone. The ongoing SDSU research will add to what scientists know about bone development. The new knowledge is one factor that can help the medical community in forming guidelines about diet and exercise to deal with health issues such as childhood obesity and the subsequent influence on adult disorders such as osteoporosis.