High bone density in young Hutterite children

We previously reported greater than average aBMD in adult Hutterites; however, it is unknown whether higher aBMD occurs at younger ages. We examined Hutterite children to test the hypotheses that aBMD Z-scores in younger (< 15 years) Hutterite children would be similar to reference data; but greater in older children after they enter the adult workforce at age 15. A secondary aim was to determine lifestyle factors associated with bone measures among Hutterite children. Hip, femoral neck, and spine BMC and aBMD were measured in 323 Hutterite children aged 8 through 19 years: 186 (108 girls) were < 15 years (younger) and 137 (87 girls) were ≥ 15 years (older). Anthropometric measurements and activity and dietary recalls were obtained. Overall, children were lighter (Z = − 0.29 ± 0.72 [mean ± SD]), shorter (Z = − 0.15 ± 0.86, and had lower BMI's (Z = − 0.27 ± 0.70) than other South Dakota children residing in the same counties (all, p ≤ 0.002). Older girls and boys had higher percent time in moderate + vigorous activity (21 ± 10% and 29 ± 11% [mean ± SD]) than younger girls and boys (15 ± 10% and 18 ± 10%, both p < 0.001). Younger girls and boys had high hip aBMD Z-scores (0.30 ± 1.0, 0.44 ± 0.97; both greater than 0 at p ≤ 0.002). Younger males had low spine Z-score (− 0.27 ± 1.15, p = 0.04). None of the Z-scores for the older ages were different from 0. Controlling for covariates, miles walked/day and grip strength were associated with greater hip bone area among girls (both, p < 0.05). Grip strength was associated with hip and femoral neck BMC and hip aBMD among boys (all, p < 0.05). Femoral neck bone area was inversely associated with calcium intake among boys (p ≤ 0.05), while higher hip BMC and spine BMC and aBMD were associated with increased vitamin D intake (all, p ≤ 0.05). Lean mass was an independent predictor of all bone measures, while fat mass was inversely associated with most measures of bone area. In summary, contrary to our hypothesis younger Hutterite children had greater hip aBMD Z scores than the normative DXA database, whereas older children did not. We speculate that high activity levels during the rapid growth phase leads to increased bone turnover and bone size; following bone consolidation later in young adulthood this will result in greater bone size and aBMD.