Bone mineral density by single photon X-ray absorptiometry in Chilean children and adolescents

To assess bone mineralization in healthy Chilean children and adolescents, considering sex, age, height, and puberty.

In a descriptive cross sectional study, the appendicular bone mineral density (BMD) was measured by single photon x-ray absorptiometry at distal (D-BMD) and ultradistal (UD-BMD) regions of the forearm, in 571 healthy children and adolescents of Valparaíso and Viña del Mar, Chile, considering their age, sex, height, calcium intake, and pubertal development according to Tanner.

Physical activity was regular; daily average calcium intake was 580 +/- 100 mg and the D-BMD and UD-BMD showed a 3 step growth pattern: Slow increments between 4 and 8 years of age in girls (r = 0.07 and r = 0.37, respectively) and between 4 and 12 years in boys (r = 0.17 and r = 0.39); sharp increases between 8 and 19 years in female adolescents (r = 0.78 and r = 0.73) and between 12 and 20 years in male adolescents (r = 0.82 and r = 0.67); and deceleration of growth from 19 years in female adolescents and 20 years in males. Considering Tanner classifications (T), boys had significant differences in mean D-BMD between T3 and T4 (p < 0.001) and between T4 and T5 (p < 0.001) and in mean UD-BMD between T3 and T4 (p < 0.001). They achieve higher values than women in adulthood. Girls showed significant differences in mean D-BMD between T3 and T4 (p = 0.003) and T4 and T5 (p < 0.001), and in mean UD-BMD between T3 and T4 (p = 0.016). Considering menarche, there was an important increment in bone mass up to 3 years after menarche, and it was significant until 2 years after for D-BMD (p < 0.02) and 1 year after for UD-BMD (p < 0.001). In girls and boys, bone mass increments did not correlate with height increments. A delay in bone mass increments was observed at early Tanner stages.

Between 4 and 8 years in girls and 4 and 12 years in boys, there is a slow increment in bone density correlated with age and sex. A steeper slope in bone growth started with puberty, correlated with Tanner stage. Bone mineral increments did not correlate with height increments. At the end of pubertal development bone acquisition slowed down. Men achieved higher bone density values than women.