Hip Bone Density is Determined by Teenage Exercise Patterns

The amount of exercise a teenage girl gets between the ages of 12 and 18 is an important determinant in the density and strength of the proximal femur, and thus a crucial factor in the prevention of hip fractures due to osteoporosis in postmenopausal women.

Results from the Penn State Young Women's Health Study indicate that bone mineral density at the proximal femur (the thigh bone that provides the ball portion of the ball and socket joint at the hip) in an 18 year old woman is a product of physical activity. The study is reported in an article by Tom Lloyd and colleagues, in the July, 2000 issue of the journal Pediatrics. Among the 81 healthy white females participating in the study, exercise was found to be a more important factor than calcium intake in reaching peak hip mineral density.

These women are part of a longitudinal (long term) project which has included data collection on their nutrient intake, height and weight gain, level of aerobic fitness, total body bone mineral content, proximal femur mineral density, and sports-exercise scores. The sports-exercise scores for the participants were determined by their own reported levels of involvement in school-based sports activities like soccer and track, extramural classes and activities like ballet and swimming, and individual exercise and sports pursuits - hiking, running, tennis, martial arts, etc. The measurements and sports-exercise scores were collected at regular intervals over the period when the girls were aged 12 to 18.

As the girls aged they gained 42% of their total bone mineral content and 19% of their bone mineral density. Bone mineral density had a positive correlation with sports-exercise scores, fitness measurements, and with total body weight. This means that as the level of physical activity (and fitness, and weight) increased, so did bone mineral density.

This does not mean that calcium is not important. The researchers emphasize that these were healthy girls, and while most of them reported calcium intake somewhat below the RDI or recommended daily intake, their intake was above the national average, and they were not undernourished in any way. There is still debate about how much calcium is needed to optimize bone mass development. And peak mineralization occurs in different parts of the skeleton at different ages so not all studies that relate diet to bone density can be compared with each other.

The take-home message of the study is that for healthy white females, it appears that the risk of hip fracture in older adulthood can be reduced by nearly 20% if adolescent and teenage girls engage in healthy levels of daily physical activity.

Each year, Medical College of Wisconsin physicians care for more than 180,000 patients, representing nearly 500,000 patient visits. Medical College physicians practice at Children's Hospital of Wisconsin, Froedtert Memorial Lutheran Hospital, the Milwaukee VA Medical Center, and many other hospitals and clinics in Milwaukee and southeastern Wisconsin.