Familial resemblance of bone mineralization, calcium intake, and physical activity in early-adolescent daughters, their mothers, and maternal grandmothers.

OBJECTIVE

To describe familial relationships among bone mineral density (BMD), calcium intake, and physical activity in early-adolescent daughters, their premenopausal mothers, and postmenopausal maternal grandmothers.

SUBJECTS

Healthy, early-adolescent daughter and premenopausal mother pairs (n=72) were enrolled in the study. In addition, a cohort of 22 postmenopausal maternal grandmothers were measured for comparison of related triads (n=22).

DESIGN

Cross-sectional measurements of hip (three sites) and lumbar spine BMD by dual energy x-ray absorptiometry (DXA), body height and weight, menstrual function, current calcium intake, and current and past physical activity patterns were assessed using recalls and questionnaires.

STATISTICAL ANALYSIS

Correlational analysis was used to establish relationships between bone characteristics and body size, menstrual function, calcium intake, and physical activity. Multiple regression analyses with backward elimination were used to examine heritability of bone characteristics in daughter-mother and mother-grandmother pairs and daughter-mother-grandmother triads. Quick cluster analysis and cross-tabulation with Pearson's chi(2) were used to evaluate familial patterns for bone characteristics and lifestyle practices.

RESULTS

Height, weight, and lumbar spine BMD were significantly correlated within mother-daughter pairs. Current and past calcium intakes were not related within pairs or triads or to BMD in the daughters or the grandmothers. A weak inverse relationship between calcium intake and the hip trochanter and lumbar spine BMD was observed in the mothers (R(2)=-0.25; P=.05). Physical activity, independent of calcium intake, was strong predictor of BMD for daughters and mothers. Among the daughters, the hertiability estimates for trochanter and lumbar spine BMD were 0.56 and 0.70, respectively (P<.01). The heritability estimate for premenopausal mothers were significant for lumbar spine BMD (h(2)=0.66; P<.01). Daughter-mother-grandmother triads with low physical activity had low femoral neck BMD whereas those with high physical activity had high femoral neck BMD (P<.001).

APPLICATIONS

Making physical activity a part of the daily routine, in addition to an adequate intake of calcium and bone-related nutrients, is an important goal for maintaining or improving bone health for women of all ages.