Racial Differences in Cortical Bone Mass, Size and Estimated Strength at the Tibial Diaphysis in Early Pubertal Children

poster abstractOsteoporotic fracture rates differ according to race, with blacks having up to half the rate of whites. The reduced fracture rate in blacks has been suggested to be due to their superior bone mass; however, mass is not the sole determinant of bone strength. Bone strength, and consequent fracture risk, is also influenced by how bone material is distributed or structured. It is likely bone structure also contributes to the lower incidence of fractures in blacks and that racial differences in bone structure have roots in childhood. The aim of this study was to assess the influence of race on pQCT-derived cortical bone mass, size and estimated strength at the tibial diaphysis in early pubertal children. 160 children were recruited, with equal subjects according to race (black, n=80; white, n=80) and sex (female, n=80; male, n=80). Subjects were at sexual maturation stages 2 or 3. Tomographic slices of the tibial diaphysis at 66% proximal from the medial malleolus were acquired using pQCT. Slices were assessed for cortical volumetric BMD (Ct.vBMD), cortical BMC (Ct.BMC), total (Tt.Ar) and cortical (Ct.Ar) area, density weighted maximum (IMAX) and minimum (IMIN) second moments of area, density-weighted polar strength-strain index (SSIP), and muscle cross-sectional area (mCSA). Group differences were assessed by two-way analysis of covariance, with race (black vs. white) and sex (female vs. male) as independent variables. Covariates included predicted years from peak height velocity (maturity offset), tibial length and mCSA. There were no interactions between race and sex (all P=0.50-0.98) or main effect for sex (all P=0.08-0.45). Blacks had 15.7% more Ct.BMC, and 10.8-11.8% larger Tt.Ar and Ct.Ar than whites (all P<0.001). The greater enhancement of Ct.BMC relative to Ct.Ar resulted in blacks having 3.6% greater Ct.vBMD than whites (P<0.001). The combination of increased cortical bone mass, size and density in blacks contributed to enhanced estimated bone strength, with IMAX, IMIN and SSIP being 20.0%, 34.5% and 25.2% greater in blacks than whites, respectively (all P<0.001). These data indicate that early pubertal black children have enhanced bone mass, size and estimated bone strength at the tibial diaphysis versus whites, independent of tibial length and mCSA. They suggest bone structural differences may contribute to observed racial differences in fracture rates and that structural divergence between races develops during childhood

Evidence for fire in the pliocene arctic in response to amplified temperature

The mid-Pliocene is a valuable time interval for investigating equilibrium climate at current atmospheric CO2 concentrations because atmospheric CO2 concentrations are thought to have been compara

Vitamin D Supplementation Does Not Impact Insulin Resistance in Black and White Children

CONTEXT: Vitamin D supplementation trials with diabetes-related outcomes have been conducted almost exclusively in adults and provide equivocal findings. OBJECTIVE: The objective of this study was to determine the dose-response of vitamin D supplementation on fasting glucose, insulin, and a surrogate measure of insulin resistance in white and black children aged 9–13 years, who participated in the Georgia, Purdue, and Indiana University (or GAPI) trial: a 12-week multisite, randomized, triple-masked, dose-response, placebo-controlled vitamin D trial. DESIGN: Black and white children in the early stages of puberty (N = 323, 50% male, 51% black) were equally randomized to receive vitamin D3 (0, 400, 1000, 2000, or 4000 IU/day) for 12 weeks. Fasting serum 25-hydroxyvitamin D (25(OH)D), glucose and insulin were assessed at baseline and weeks 6 and 12. Homeostasis model assessment of insulin resistance was used as a surrogate measure of insulin resistance. Statistical analyses were conducted as intent-to-treat using a mixed effects model. RESULTS: Baseline serum 25(OH)D was inversely associated with insulin (r = −0.140, P = 0.017) and homeostasis model assessment of insulin resistance (r = −0.146, P = 0.012) after adjusting for race, sex, age, pubertal maturation, fat mass, and body mass index. Glucose, insulin, and insulin resistance increased (F > 5.79, P < .003) over the 12 weeks, despite vitamin D dose-dependent increases in serum 25(OH)D. CONCLUSIONS: Despite significant baseline inverse relationships between serum 25(OH)D and measures of insulin resistance, vitamin D supplementation had no impact on fasting glucose, insulin, or a surrogate measure of insulin resistance over 12 weeks in apparently healthy children

Voluntary Wheel Running Has Beneficial Effects in a Rat Model of CKD-Mineral Bone Disorder (CKD-MBD)

Background Reduced bone and muscle health in individuals with CKD contributes to their higher rates of morbidity and mortality. Methods We tested the hypothesis that voluntary wheel running would improve musculoskeletal health in a CKD rat model. Rats with spontaneous progressive cystic kidney disease (Cy/+ IU) and normal littermates (NL) were given access to a voluntary running wheel or standard cage conditions for 10 weeks starting at 25 weeks of age when the rats with kidney disease had reached stage 2–3 of CKD. We then measured the effects of wheel running on serum biochemistry, tissue weight, voluntary grip strength, maximal aerobic capacity (VO2max), body composition and bone micro-CT and mechanics. Results Wheel running improved serum biochemistry with decreased creatinine, phosphorous, and parathyroid hormone in the rats with CKD. It improved muscle strength, increased time-to-fatigue (for VO2max), reduced cortical porosity and improved bone microarchitecture. The CKD rats with voluntary wheel access also had reduced kidney cystic weight and reduced left ventricular mass index. Conclusions Voluntary wheel running resulted in multiple beneficial systemic effects in rats with CKD and improved their physical function. Studies examining exercise interventions in patients with CKD are warranted