June 11, 2004 -- Exercise works better than calcium in building strong bones, a new study shows. It's a new advisory for teen girls: Physical activity is more important than drinking milk for offsetting osteoporosis.
That finding disputes the current message given to women and girls, writes lead researcher Tom Lloyd, PhD, an epidemiologist with the Penn State University College of Medicine. His paper appears in the current issue of the Journal of Pediatrics.
"Although calcium intake is often cited as the most important factor for healthy bones, our study suggests that exercise is really the predominant lifestyle determinant of bone strength in young women," Lloyd says in a news release.
The advent of high-tech bone density screening -- dual energy X-ray absorptiometry (DEXA) -- has given researchers a tool to measure bone density and indirectly measure bone strength. That has also helped researchers understand the importance that various factors like calcium and physical activity play in building bone and preventing osteoporosis.
Studies have shown that as much bone is built between ages 13 and 15 as that which is lost to aging and osteoporosis during the last four decades of life. Therefore, it's crucial that a girl works on optimizing the bone-building process during adolescence as the best protection against osteoporosis, writes Lloyd.
To better understand the factors at work, Lloyd studied 80 girls about 12 years old when the study began.
For 10 years, he and his colleagues tracked the girls' bone strength through yearly DEXA scans of hip bones. They also got information on calcium intake, birth control use (which is reported to help build bone), and physical activity the girls got -- whether it was sports, marching band, dance, aerobics classes, running, walking, or another activity.
- Calcium intake and birth control pill use had no significant affect on bone strength, Lloyd reports.
- Sports and exercise did make a big difference -- increasing the young women's bone mineral density at the hip 3%-5%.
"We have shown that ages 12 to 16 are important years for bone [building] and that adolescent physical activity is positively related to [bone muscle density] and bone strength of the young adult hip," writes Lloyd.
His study has one limitation: It only involved white girls. Other ethnic and racial groups must be studied to provide a more complete picture of osteoporosis, calcium, and physical activity, he writes.