Self-reported ballet classes undertaken at age 10-12 years and hip bone mineral density in later life

The major effect of weightbearing exercise on adult bone mass may be exerte d during childhood. We examined the relationship between reported hours of ballet classes per week undertaken as a child and adult bone mineral densit y (BMD) at the hip, spine, and forearm. We performed a retrospective cohort study in 99 female retired dancers (mean age 51 years, SD 14 years) and 99 normal controls, derived from a twin study, matched hierarchically for age , height, weight and menopausal status. Starting age of ballet was recalled and weekly hours of ballet as a child was self-reported on two occasions. BMD was measured using dual-energy X-ray absorptiometry and reported as a Z -score. Self-reported hours of ballet class undertaken per week at each age between 10 and 12 years was positively associated with a difference in BMD between dancers and controls at both the femoral neck site (beta = 0.73, p = 0.001) and the total hip site (beta = 0.55, p < 0.01). These association s were unaffected by adjustment for covariates including measures of adult activity (current physical activity, years of fulltime ballet), measures of menstrual disturbance (age of menarche, history of irregular menses): diet ary history (calcium intake as a child, adolescent or adult) or lifestyle f actors (lifetime smoking, lifetime alcohol). Although starting age of balle t was negatively associated with weight-adjusted within-pair hip BMD differ ence, it was no longer associated after adjustment for weekly hours of ball et. There was no relationship between hours of ballet undertaken as a child and differences in BMD at the lumbar spine or upper limb, at any age. Our data suggest that classical ballet classes undertaken between the ages of 1 0 and 12 years are independently and positively associated with a differenc e in hip BMD between dancers and controls. The findings are consistent with the hypothesis that this age range identifies a stage of development when the proximal femur is particularly responsive to weightbearing exercise.