He fit of these equations, assess for overfitting (adjusting as necessary), and calibrate using external samples. Methods We evaluated potential overfitting using the original Pediatric Bone Mineral Accrual Study (PBMAS; 79 boys and 72 girls; 7.5–17.5 yr). We assessed change in R2 and standard error of the estimate (SEE) with the addition of predictor variables. We determined the effect of within-subject correlation using cluster-robust variance and fivefold random splitting followed by forward-stepwise regression. We used dominant predictors from these splits to assess predictive abilities of various models. We calibrated using participants from the Healthy Bones Study III (HBS-III; 42 boys and 39 girls; 8.9–18.9 yr) and Harpenden Growth Study (HGS; 38 boys and 32 girls; 6.5–19.1 yr). Results Change in R2 and SEE was negligible when later predictors were added during step-by-step refitting of the original equations, suggesting overfitting. After redevelopment, new models included age × sitting height for boys (R2, 0.91; SEE, 0.51) and age × height for girls (R2, 0.90; SEE, 0.52). These models calibrated well in external samples; HBS boys: b0, 0.04 (0.05); b1, 0.98 (0.03); RMSE, 0.89; HBS girls: b0, 0.35 (0.04); b1, 1.01 (0.02); RMSE, 0.65; HGS boys: b0, −0.20 (0.02); b1, 1.02 (0.01); RMSE, 0.85; HGS girls: b0, −0.02 (0.03); b1, 0.97 (0.02); RMSE, 0.70; where b0 equals calibration intercept (standard error (SE)) and b1 equals calibration slope (SE), and RMSE equals root mean squared error (of prediction). We subsequently developed an age × height alternate for boys, allowing for predictions without sitting height. Conclusion Our equations provided good fits in external samples and provide an alternative to commonly used models. Original prediction equations were simplified with no meaningful increase in estimation error....

In this cross-sectional study, we aimed to predict age-related changes in bone microarchitecture and strength at the distal radius (DR) and distal tibia (DT) in 644 Canadian adults (n = 442 women and 202 men) aged 20 to 99 years. We performed a standard morphologic analysis of the DR and DT with high-resolution peripheral quantitative computed tomography (pQCT) and used finite-element analysis (FEA) to estimate bone strength (failure load) and the load distribution. We also calculated a DR load-to-strength ratio as an estimate of forearm fracture risk. Total bone area, which was 33% larger in young men at both sites, changed similarly with age in women and men at the DT but increased 17% more in men than in women at the DR (p < .001). Trabecular number and thickness (Tb.Th) were 7% to 20% higher in young men than in young women at both sites, and with the exception of Tb.Th at the DR, which declined more with age in men (−16%) than in women (−2%, p < .01), the age-related decline in these outcomes was similar in women and in men. In the cortex, porosity (Ct.Po) was 31% to 44% lower in young women than in young men but increased 92% to 176% more with age in women than in men (p < .001). The DR cortex carried 14% more load in young women than in young men, and the percentage of load carried by the DR cortex did not change with age in women but declined by 17% in men (p < .01). FEA-estimated bone strength was 34% to 47% greater in young men, but the predicted change with age was similar in both sexes. In contrast, the load-to-strength ratio increased 27% more in women than in men with age (p < .01). These results highlight important site- and sex-specific differences in patterns of age-related bone loss. In particular, the trends for less periosteal expansion, more porous cortices, and a greater percentage of load carried by the DR cortex in women may underpin sex differences in forearm fracture risk. © 2011 American Society for Bone and Mineral Research.

Background: The menopausal transition is characterized by rapid bone loss. Few data exist on the role of nutrition. Objective: The objective of the study was to ascertain which dietary factors influence perimenopausal skeletal loss. Design: A longitudinal study was conducted of 891 women aged 45–55 y at baseline and 50–59 y at follow-up 5–7 y later. Bone mineral density (BMD) was measured by using dual-energy X-ray absorptiometry at the lumbar spine and femoral neck (FN). Nutrient intakes were assessed after the baseline visit and 5 y later, by using the same food-frequency questionnaire. Results: After adjustment for energy intake and other confounders, higher intakes of calcium were correlated with change in FN BMD (ie, reduced loss) (r = 0.073, P < 0.05), and the intake of modest amounts of alcohol was associated with less lumbar spine bone loss (P < 0.01 for quartile of alcohol intake). Greater FN BMD loss was associated with increased intake of polyunsaturated fatty acids (r = −0.110, P < 0.01), monounsaturated fatty acids (r = −0.069, P < 0.05), retinol (r = −0.067; P < 0.05), and vitamin E (r = −0.110; P < 0.01). The latter 2 nutrients were highly correlated with polyunsaturated fatty acids. For premenopausal women, calcium and nutrients found in fruit and vegetables (vitamin C, magnesium, and potassium) were associated with FN BMD, and calcium, vitamin C, and magnesium were associated with change in FN BMD. Conclusions: Although menopausal status and hormone replacement therapy use dominate women's bone health, diet may influence early postmenopausal bone loss. Fruit and vegetable intake may protect against premenopausal bone loss.

Increases in cortical porosity (Ct.Po) and decreases in cortical thickness (Ct.Th) are associated with increased bone fragility. The purpose of this study was to validate an autosegmentation method for high-resolution peripheral quantitative computed tomography (HR-pQCT) scans to measure Ct.Po and Ct.Th and use it to compare Ct.Po and Ct.Th between pre- and postmenopausal women with normal, osteopenic, and osteoporotic areal bone mineral density (aBMD). The Ct.Po and Ct.Th measurements were validated using cadaver forearms (n = 10) and micro-computed tomography (µCT) as the gold standard. The analysis was applied to distal radius and tibia HR-pQCT scans from a subset of participants from the Calgary, Alberta, cohort of the Canadian Multicentre Osteoporosis Study (n = 280, 18 to 90 years). Analysis of covariance compared Ct.Po and Ct.Th outcomes between 63 normal premenopausal (dual-energy X-ray absorptiometry femoral neck T-score > −1), 87 normal postmenopausal, 121 osteopenic postmenopausal, and 9 osteoporotic postmenopausal women. Linear regression analysis and Bland-Altman plots were used to assess the agreement between the HR-pQCT and µCT measurements, resulting in r2 values of 0.80 for Ct.Po and 0.98 for Ct.Th. At both sites, Ct.Po was higher in postmenopausal (all groups) than in premenopausal women (3.2% to 12.9%, p < .001). Ct.Th was not significantly different between normal premenopausal and postmenopausal women at either site; however, both osteopenic and osteoporotic women had thinner (−12.8% to −30.3%, p < .01), more porous (2.1% to 8.1%, p < .001) cortices than normal postmenopausal women. Our method offers promise as a valuable tool to measure Ct.Po and Ct.Th in vivo and investigate associations among cortical bone structure, age, and disease status. © 2010 American Society for Bone and Mineral Research.

The purpose of this study was twofold: 1) to evaluate the effectiveness of a school-based physical activity intervention, Action Schools! BC (AS! BC), for maintaining academic performance in a multiethnic group of elementary children, and 2) to determine whether boys and girls' academic performance changed similarly after participation in AS! BC. This was a 16-month cluster randomized controlled trial. Ten schools were randomized to intervention (INT) or usual practice (UP). One INT school administered the wrong final test, and one UP school graded their own test, so both were excluded. Thus, eight schools (six INT, two UP) were included in the final analysis. Children (143 boys, 144 girls) in grades 4 and 5 were recruited for the study. We used the Canadian Achievement Test (CAT-3) to evaluate academic performance (TotScore). Weekly teacher activity logs determined amounts of physical activity delivered by teachers to students. Physical activity was determined with the Physical Activity Questionnaire for Children (PAQ-C). Independent t-tests compared descriptive variables between groups and between boys and girls. We used a mixed linear model to evaluate differences in TotScore at follow-up between groups and between girls and boys. Physical activity delivered by teachers to children in INT schools was increased by 47 min x wk(-1) (139 +/- 62 vs 92 +/- 45, P < 0.001). Participants attending UP schools had significantly higher baseline TotScores than those attending INT schools. Despite this, there was no significant difference in TotScore between groups at follow-up and between boys and girls at baseline and follow-up. The AS! BC model is an attractive and feasible intervention to increase physical activity for students while maintaining levels of academic performance.