Predictors of skeletal calcium accretion in adolescents from pooled metabolic balance studies
Abstract
Peak bone mass (PBM) attained in the first few decades of life is a major determinant of risk of late life osteoporosis. From our pooled database of 487 observations on 265 boys and girls aged 10 to 16 years, the influence of calcium intake, race, sex, body size, sexual maturation, growth factors, calcium homeostatic hormones, and physical activity on skeletal calcium accretion was assessed. Our first objective was to determine predictors of calcium retention in adolescent boys as done previously in girls to provide a starting point for further predictive models. In a nonlinear model of calcium retention in boys, calcium intake explained 21.7% of the variation in calcium retention and serum IGF-1 explained an additional 11.5%, where higher serum IGF-1 predicted higher calcium retention. Using a two-phase regression model of calcium retention in the entire pooled database, calcium intake, BMI, race, and sex predicted 26% of the variability in calcium retention, and there was a significant BMI and calcium intake interaction. Calcium retention was higher with greater BMI only at higher calcium intakes. This indicates that overweight and obese adolescents may benefit more from increasing calcium intake compared to normal weight adolescents, which may decrease the increased rate of childhood fractures observed in overweight adolescents. Additional predictors of calcium retention were identified. In boys, calcium intake, BMI, serum IGF-1, and serum 25OHD explained 40.5% of the variation in calcium retention. In girls, calcium intake, BMI, race, age, and serum PTH explained 27.9 % of the variation in calcium retention. The greatest predictor of calcium retention in both models was calcium intake, explaining 31.0% and 11.0% of the variation in calcium retention in boys and girls, respectively. As only 20-40% of the variation in PBM is determined by environmental factors, calcium intake is a major lifestyle factor for determining PBM. Measures of body size, growth and maturity, race, and regulators of calcium metabolism were additional factors that influenced calcium retention. Further experimental intervention data is needed to test if our predictions for calcium retention translate into actual skeletal gains in adolescents.
Degree
Ph.D.
Advisors
Weaver, Purdue University.
Subject Area
Nutrition
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