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Fitting of BMD with consideration of confounding parameters
Abstracts / Bone 45 (2009) S59–S111 h Department of Physiology, School of Medicine, University of Granada, Granada, Spain
Introduction and objectives: Physical activity has an important osteogenic effect. Osteocalcin (OC), aminoterminal propeptide of type I procollagen (PINP) and beta crosslaps have been described as markers of bone metabolism. We aimed to describe the association between the concentrations of those markers and objectively measured physical activity. Methods: Both blood samples and objectively measured PA were obtained in 89 Spanish adolescents (41 males and 48 females), aged 12.5–17.5 years, within the framework of the HELENA study. Serum osteocalcin, PINP and beta crosslaps concentrations were determined by electrochemiluminescence immunoassay. Physical Activity (PA) was measured during 7 days using ActiGraph accelerometers. Subjects were divided into sedentary and active groups according to PA recommendations [1]. The sedentary group included subjects who did less than a mean of 1 h/day of Moderate–Vigorous Physical Activity (MVPA); and the active group included those who did a mean of one or more hours of MVPA. Independent Samples T-Test was applied to determine gender and active/sedentary differences for each bone marker. Pearson correlations were applied to determine the association between bone markers and objectively measured physical activity. Results: Osteocalcin correlated with low (r = 0.401, p < 0.05) and moderate intensity PA (r = 0.338, p < 0.05) and n-telopeptides also correlate with low intensity PA (r = 0.460, p < 0.05) in males. In females, PINP correlated with moderate (r = − 0.301, p < 0.05), vigorous (r = − 0.304, p < 0.05) and MVPA (r = −0.354, p < 0.05). Table 1 shows concentration of osteocalcin, PINP and beta crosslaps in sedentary and active males and females. PINP were significantly higher in sedentary females compared with active females (p < 0.05). Table 1 Bone marker concentrations according to active or sedentary lifestyle. Male
Sed
Act
p
Female
Osteocalcin (ng/mL)
PINP (ng/mL)
Beta crosslaps (ng/mL)
Osteocalcin (ng/mL)
PINP (ng/mL)
Beta crosslaps (ng/mL)
111.88 ± 47.1
775.56 ± 497.98 n = 20 673.35 ± 353.72 n = 17 0.484
1.71 ± 0.59 n = 13 1.43 ± 0.49 n = 13 0.208
64.92 ± 44.96 n = 37 54.16 ± 28.26 n = 11 0.459
321.11 ± 236.65 n = 35 185.34 ± 105.11 n = 10 0.013
1.05 ± 0.66 n = 26 0.72 ± 0.14 n=7 0.196
n = 21 133.3 ± 56.46 n = 20 0.194
Conclusions: There was a significant relationship between low and moderate PA intensity for osteocalcin; and again low PA intensity with PINP in males. PINP correlated inversely with MVPA in females. References [1] Strong WB, Malina RM, Blimkie CJ, et al. Evidence based physical activity for school-age youth. J Pediatr. 2005;146:732–7. doi:10.1016/j.bone.2009.04.123
PT-22 Fitting of BMD with consideration of confounding parameters T.N. Hangartnera, D.F. Shorta, B.S. Zemelb, V. Gilsanzc, H.J. Kalkwarfd, J.M. Lappee, S. Oberfieldf, J.A. Shepherdg, K. Winerh a Wright State University, Dayton, OH, USA b Children's Hospital of Philadelphia, Philadelphia, PA, USA c Children's Hospital Los Angeles, Los Angeles, CA, USA d Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA e Creighton University, Omaha, NE, USA f Columbia University, New York, NY, USA
S87
g
University of California at San Francisco, San Francisco, CA, USA National Institute of Child Health and Human Development, Bethesda, MD, USA h
This study evaluated a strategy of creating normal BMD data, taking into account potentially relevant anthropometric and other variables. The Bone Mineral Density in Childhood Study1, is a prospective, longitudinal study of ∼ 2000 healthy children ages 6 to 20 years. 7661 observations from this longitudinal study were used. The variables included spine BMD, age, gender, race, height, weight, whole-body percent fat and sexual maturity. Due to the relatively small number of data points when subgroups of age, gender, race, weight, etc., were considered, a smoothing approach was required. An additional concern was the mutual dependency of variables, for which smoothing of one parameter might result in undesired smoothing of another parameter. We transformed the given variable space first into an orthogonal space of independent variables. We then applied smoothing to these orthogonal variables and back transformed them into the original space. The goodness of fit was evaluated by omitting variables to determine which predictive parameters were most relevant. We found that (i) an age/gender/race (black/non black) model provides a root mean square error (RMSE) of 0.1029 g/cm2, similar to that of a previous publication2; (ii) omitting race and adding weight and percent body fat improves the model's RMSE to 0.0862 g/cm2; (iii) replacing weight by height increases the RMSE by 15% to 0.0989 g/ cm2; and (iv) male and female sexual maturity indicators with weight in the model improve the RMSE only by 0.001 g/cm2; with height but not weight in the model, the sexual maturity indicators improve the RMSE by 0.006 g/cm2. Our model presents a possible approach to account for height, as suggested by the ISCD3, or other anthropometric parameters in interpreting BMD in pediatrics. 1 Sponsored by the National Institute for Child Health and Human Development. 2 Kalkwarf H. et al., J Clin Endocrinol Metab 92:2087–2099, 2007. 3 http://www.iscd.org/Visitors/positions/OfficialPositionsText. cfm#PEDIATRIC. doi:10.1016/j.bone.2009.04.124
PT-23 Predictors of bone mineral density and content in 7 year old children H. Hrafnkelsson, G. Sigurdsson, K. Magnusson, E. Johannsson, E. Sigurdsson University of Iceland, Reykjavik, Iceland Introduction: It is likely that the bone mass attained during childhood is an important determinant of the risk of fracture later in life. The purpose of this study was to evaluate bone the lumbar vertebrae and hips of 7 years old children in Iceland and see if gender, height, lean tissue mass and fat mass does predict BMD and BMC in the lumbar vertebra and hip. Material and methods: This study is a cross-sectional study of seven-year-old children from six elementary schools in Reykjavík. All children attending second class in these six schools were invited to participate. 211 (65%) out of 326 children did have Dual energy X-ray absorptiometry (DXA) scan with paediatric program. Results: Both BMD and BMC had a positive correlation to height, lean tissue mass and fat mass but when analyzed with linear regression it was only the lean tissue mass that predicted BMC in the hip explaining about 54% of the variance (R square). Lean tissue mass could explain 57% (R square) of BMC in the vertebra but this did increase to 60% when height and gender was put in the model. Fat mass did not show positive relation to BMC or BMD in linear
Introduction and objectives: Physical activity has an important osteogenic effect. Osteocalcin (OC), aminoterminal propeptide of type I procollagen (PINP) and beta crosslaps have been described as markers of bone metabolism. We aimed to describe the association between the concentrations of those markers and objectively measured physical activity. Methods: Both blood samples and objectively measured PA were obtained in 89 Spanish adolescents (41 males and 48 females), aged 12.5–17.5 years, within the framework of the HELENA study. Serum osteocalcin, PINP and beta crosslaps concentrations were determined by electrochemiluminescence immunoassay. Physical Activity (PA) was measured during 7 days using ActiGraph accelerometers. Subjects were divided into sedentary and active groups according to PA recommendations [1]. The sedentary group included subjects who did less than a mean of 1 h/day of Moderate–Vigorous Physical Activity (MVPA); and the active group included those who did a mean of one or more hours of MVPA. Independent Samples T-Test was applied to determine gender and active/sedentary differences for each bone marker. Pearson correlations were applied to determine the association between bone markers and objectively measured physical activity. Results: Osteocalcin correlated with low (r = 0.401, p < 0.05) and moderate intensity PA (r = 0.338, p < 0.05) and n-telopeptides also correlate with low intensity PA (r = 0.460, p < 0.05) in males. In females, PINP correlated with moderate (r = − 0.301, p < 0.05), vigorous (r = − 0.304, p < 0.05) and MVPA (r = −0.354, p < 0.05). Table 1 shows concentration of osteocalcin, PINP and beta crosslaps in sedentary and active males and females. PINP were significantly higher in sedentary females compared with active females (p < 0.05). Table 1 Bone marker concentrations according to active or sedentary lifestyle. Male
Sed
Act
p
Female
Osteocalcin (ng/mL)
PINP (ng/mL)
Beta crosslaps (ng/mL)
Osteocalcin (ng/mL)
PINP (ng/mL)
Beta crosslaps (ng/mL)
111.88 ± 47.1
775.56 ± 497.98 n = 20 673.35 ± 353.72 n = 17 0.484
1.71 ± 0.59 n = 13 1.43 ± 0.49 n = 13 0.208
64.92 ± 44.96 n = 37 54.16 ± 28.26 n = 11 0.459
321.11 ± 236.65 n = 35 185.34 ± 105.11 n = 10 0.013
1.05 ± 0.66 n = 26 0.72 ± 0.14 n=7 0.196
n = 21 133.3 ± 56.46 n = 20 0.194
Conclusions: There was a significant relationship between low and moderate PA intensity for osteocalcin; and again low PA intensity with PINP in males. PINP correlated inversely with MVPA in females. References [1] Strong WB, Malina RM, Blimkie CJ, et al. Evidence based physical activity for school-age youth. J Pediatr. 2005;146:732–7. doi:10.1016/j.bone.2009.04.123
PT-22 Fitting of BMD with consideration of confounding parameters T.N. Hangartnera, D.F. Shorta, B.S. Zemelb, V. Gilsanzc, H.J. Kalkwarfd, J.M. Lappee, S. Oberfieldf, J.A. Shepherdg, K. Winerh a Wright State University, Dayton, OH, USA b Children's Hospital of Philadelphia, Philadelphia, PA, USA c Children's Hospital Los Angeles, Los Angeles, CA, USA d Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA e Creighton University, Omaha, NE, USA f Columbia University, New York, NY, USA
S87
g
University of California at San Francisco, San Francisco, CA, USA National Institute of Child Health and Human Development, Bethesda, MD, USA h
This study evaluated a strategy of creating normal BMD data, taking into account potentially relevant anthropometric and other variables. The Bone Mineral Density in Childhood Study1, is a prospective, longitudinal study of ∼ 2000 healthy children ages 6 to 20 years. 7661 observations from this longitudinal study were used. The variables included spine BMD, age, gender, race, height, weight, whole-body percent fat and sexual maturity. Due to the relatively small number of data points when subgroups of age, gender, race, weight, etc., were considered, a smoothing approach was required. An additional concern was the mutual dependency of variables, for which smoothing of one parameter might result in undesired smoothing of another parameter. We transformed the given variable space first into an orthogonal space of independent variables. We then applied smoothing to these orthogonal variables and back transformed them into the original space. The goodness of fit was evaluated by omitting variables to determine which predictive parameters were most relevant. We found that (i) an age/gender/race (black/non black) model provides a root mean square error (RMSE) of 0.1029 g/cm2, similar to that of a previous publication2; (ii) omitting race and adding weight and percent body fat improves the model's RMSE to 0.0862 g/cm2; (iii) replacing weight by height increases the RMSE by 15% to 0.0989 g/ cm2; and (iv) male and female sexual maturity indicators with weight in the model improve the RMSE only by 0.001 g/cm2; with height but not weight in the model, the sexual maturity indicators improve the RMSE by 0.006 g/cm2. Our model presents a possible approach to account for height, as suggested by the ISCD3, or other anthropometric parameters in interpreting BMD in pediatrics. 1 Sponsored by the National Institute for Child Health and Human Development. 2 Kalkwarf H. et al., J Clin Endocrinol Metab 92:2087–2099, 2007. 3 http://www.iscd.org/Visitors/positions/OfficialPositionsText. cfm#PEDIATRIC. doi:10.1016/j.bone.2009.04.124
PT-23 Predictors of bone mineral density and content in 7 year old children H. Hrafnkelsson, G. Sigurdsson, K. Magnusson, E. Johannsson, E. Sigurdsson University of Iceland, Reykjavik, Iceland Introduction: It is likely that the bone mass attained during childhood is an important determinant of the risk of fracture later in life. The purpose of this study was to evaluate bone the lumbar vertebrae and hips of 7 years old children in Iceland and see if gender, height, lean tissue mass and fat mass does predict BMD and BMC in the lumbar vertebra and hip. Material and methods: This study is a cross-sectional study of seven-year-old children from six elementary schools in Reykjavík. All children attending second class in these six schools were invited to participate. 211 (65%) out of 326 children did have Dual energy X-ray absorptiometry (DXA) scan with paediatric program. Results: Both BMD and BMC had a positive correlation to height, lean tissue mass and fat mass but when analyzed with linear regression it was only the lean tissue mass that predicted BMC in the hip explaining about 54% of the variance (R square). Lean tissue mass could explain 57% (R square) of BMC in the vertebra but this did increase to 60% when height and gender was put in the model. Fat mass did not show positive relation to BMC or BMD in linear