Heterogeneity of fracture pathogenesis in urban South African children: The birth to twenty cohort

Abstract

South African black children fracture less than white children. Differences in bone mass, body composition, and physical activity may be contributing risk factors. This study aimed to investigate the association between fracture prevalence, bone mass, and physical activity in South African children. Using the Bone Health cohort of the Birth to Twenty longitudinal study, we retrospectively obtained information of lifetime fractures until age 15 years in 533 subjects. Whole-body bone mineral content (BMC), bone area (BA), fat mass (FM), and lean mass (LM) (measured by dual-energy X-ray absorptiometry [DXA]), anthropometric data, physical activity scores, and skeletal maturity were obtained at ages 10 and 15 years. Nonfracturing black females were used as the control group and comparisons were made between those who did and did not fracture within the same sex and ethnic groups. Of the 533 subjects, 130 (24%) reported a fracture (black, 15%; white, 41.5%; p < 0.001). White males who fractured were significantly taller (10 years, p < 0.01), more physically active (15 years, p < 0.05) and had higher LM (10 years, p ¼ 0.01; 15 years, p < 0.001), whereas white females who fractured were fatter (10 and 15 years, p ¼ 0.05 and p < 0.05, respectively), than their nonfracturing peers. White males who fractured had greater BA and BMC at all sites at 10 and 15 years compared to their nonfracturing peers after adjusting for differences in height and weight; BA and BMC were similar in each of the other sex and ethnic groups. No anthropometric or bone mass differences were found between black children with and without fractures. The factor associated with fractures in white males appears to be participation in sports activities, while in white females obesity appears to play a role. No contributing factors in black males and females were found, and needs further elucidation. ß

Fracture patterns and bone mass in South African adolescent–mother pairs: the Birth to Twenty cohort

“…However, in our earlier study of the Bt20 cohort [30], we did not find an inverse association between fracture history prevalence and bone mass at two time points during childhood and adolescence. In fact, in white males, there was a positive association between fracture risk and bone mass [30], possibly associated with increased contact sport participation [19]. Thus, the association between maternal LS BMC and adolescent fracture risk might be a proxy for structural differences in the adolescents, with low maternal BMC indicating poorer adolescent bone strength rather than differences in bone mass per se.…”

“…Intuitively, this association should not be surprising as several studies, although not all [25–28], have shown that children who had fracture(s) tend to have reduced BMC and BA compared to their peers who had no fractures, and genetic inheritance (maternal and paternal bone mass) plays a large role in determining childhood BMC, BA and peak bone mass [29]. However, in our earlier study of the Bt20 cohort [30], we did not find an inverse association between fracture history prevalence and bone mass at two time points during childhood and adolescence. In fact, in white males, there was a positive association between fracture risk and bone mass [30], possibly associated with increased contact sport participation [19].…”

“…Eighty-nine percent (42/48) had confirmed that they had had a radiograph performed, three did not and two could not remember. Finally, this study did not include confounding variables such as vitamin D levels, calcium intake, physical activity scores or socioeconomic status, but the relationship between sports activities and fractures has been reported previously in this cohort [30]. …”

Calcium and Vitamin D Metabolism in Children in Developing Countries

“…These results differ from those reported for African-American and non-black children in the USA, where African-American children have greater bone area and BMC at all measured sites (lumbar spine, hip, radius, and whole body) than non-black children [48]. In South Africa, despite the lower calcium intakes and the poorer growth of black children, they have a fracture incidence approximately half that of white children even though X-ray absorptiometry-measured bone mass is similar at most skeletal sites [51]. …”

Racial Disparity in Fracture Risk between White and Nonwhite Children in the United States

“…A study of English children (3, 4) suggested a higher fracture rate in whites compared with non-whites, although statistical significance was not established. A study of South African children found the rate of fractures for white children to be almost twice that of children of African ancestry (5, 6). The purpose of this prospective, multi-center study was to examine race/ethnicity as a risk factor for fracture in a large, diverse cohort of children and adolescents from different regions across the United States (U.S.).…”