Iowa Bone Development Study Research Articles

The effect of family and friend support on physical activity through adolescence: a longitudinal study.

BackgroundThis study examined if family and friend support predicted adolescent physical activity (PA) across a five-year time span.MethodsThe Iowa Bone Development Study collected objective measures of physical activity and self-report of physical activity psychosocial factors at ages 13 (n = 306), 15 (n = 356), and 17 yr (n = 317). Total moderate and vigorous-intensity PA (MVPA) and MVPA after 3 pm on weekdays (MVPA-PM Weekday) were measured using ActiGraph accelerometers. Family Support for PA and Friend Support for PA scales were measured using the Choices questionnaire. Models were adjusted for SES (mother’s education) and somatic maturity (Mirwald predictive equations for maturity offset). Spearman correlation coefficients examined tracking of scales at ages 13, 15 and 17. Logistic regression estimated the odds ratio for being in the lowest tertile of each scale at age 17 if in the lowest tertile at age 13. Linear mixed regression models investigated associations between these scales and MVPA outcomes over time.ResultsTwo- and five-year intra-variable tracking associations for Family Support and Friend Support scales were moderate (r = 0.32–0.58), except for the comparison between age 13 and age 17 Friend Support for girls, which resulted in a low association (r = 0.26). Boys and girls in the lowest tertile for support at age 13 were more likely to remain in the lowest tertile at age 17 compared to those in the middle and upper tertiles. The regression models indicated that when all other factors were held constant, an increase in family and/or friend support resulted in an increase in both MVPA outcomesConclusionsFrom early to late adolescence, support for PA from the family and/or support from friends results in higher levels of total and discretionary MVPA. However, the importance of support in predicting MVPA decreased with age.

Automated cortical bone segmentation for multirow-detector CT imaging with validation and application to human studies.

Cortical bone supports and protects human skeletal functions and plays an important role in determining bone strength and fracture risk. Cortical bone segmentation at a peripheral site using multirow-detector CT (MD-CT) imaging is useful for in vivo assessment of bone strength and fracture risk. Major challenges for the task emerge from limited spatial resolution, low signal-to-noise ratio, presence of cortical pores, and structural complexity over the transition between trabecular and cortical bones. An automated algorithm for cortical bone segmentation at the distal tibia from in vivo MD-CT imaging is presented and its performance and application are examined. The algorithm is completed in two major steps-(1) bone filling, alignment, and region-of-interest computation and (2) segmentation of cortical bone. After the first step, the following sequence of tasks is performed to accomplish cortical bone segmentation-(1) detection of marrow space and possible pores, (2) computation of cortical bone thickness, detection of recession points, and confirmation and filling of true pores, and (3) detection of endosteal boundary and delineation of cortical bone. Effective generalizations of several digital topologic and geometric techniques are introduced and a fully automated algorithm is presented for cortical bone segmentation. An accuracy of 95.1% in terms of volume of agreement with manual outlining of cortical bone was observed in human MD-CT scans, while an accuracy of 88.5% was achieved when compared with manual outlining on postregistered high resolution micro-CT imaging. An intraclass correlation coefficient of 0.98 was obtained in cadaveric repeat scans. A pilot study was conducted to describe gender differences in cortical bone properties. This study involved 51 female and 46 male participants (age: 19-20 yr) from the Iowa Bone Development Study. Results from this pilot study suggest that, on average after adjustment for height and weight differences, males have thicker cortex (mean difference 0.33 mm and effect size 0.92 at the anterior region) with lower bone mineral density (mean difference -28.73 mg/cm(3) and effect size 1.35 at the posterior region) as compared to females. The algorithm presented is suitable for fully automated segmentation of cortical bone in MD-CT imaging of the distal tibia with high accuracy and reproducibility. Analysis of data from a pilot study demonstrated that the cortical bone indices allow quantification of gender differences in cortical bone from MD-CT imaging. Application to larger population groups, including those with compromised bone, is needed.

Objectively measured physical activity predicts hip and spine bone mineral content in children and adolescents ages 5-15 years: iowa bone development study.

This study examined the association between physical activity (PA) and bone mineral content (BMC; gram) from middle childhood to middle adolescence and compared the impact of vigorous-intensity PA (VPA) over moderate- to vigorous-intensity PA (MVPA). Participants from the Iowa bone development study were examined at ages 5, 8, 11, 13, and 15 years (n = 369, 449, 452, 410, and 307, respectively). MVPA and VPA (minutes per day) were measured using ActiGraph accelerometers. Anthropometry was used to measure body size and somatic maturity. Spine BMC and hip BMC were measured via dual-energy x-ray absorptiometry. Sex-specific multi-level linear models were fit for spine BMC and hip BMC, adjusted for weight (kilogram), height (centimeter), linear age (year), non-linear age (year2), and maturity (pre peak height velocity vs. at/post peak height velocity). The interaction effects of PA × maturity and PA × age were tested. We also examined differences in spine BMC and hip BMC between the least (10th percentile) and most (90th percentile) active participants at each examination period. Results indicated that PA added to prediction of BMC throughout the 10-year follow-up, except MVPA, did not predict spine BMC in females. Maturity and age neither modify the PA effect for males nor females. At age 5, the males at the 90th percentile for VPA had 8.5% more hip BMC than males in the 10th percentile for VPA. At age 15, this difference was 2.0%. Females at age 5 in the 90th percentile for VPA had 6.1% more hip BMC than those in the 10th percentile for VPA. The age 15 difference was 1.8%. VPA was associated with BMC at weight-bearing skeletal sites from childhood to adolescence, and the effect was not modified by maturity or age. Our findings indicate the importance of early and sustained interventions that focus on VPA. Approaches focused on MVPA may be inadequate for optimal bone health, particularly for females.

Objectively measured physical activity trajectories predict adolescent bone strength: Iowa Bone Development Study

BackgroundPhysical activity improves bone strength and reduces the risk for osteoporotic fractures. However, there are substantial gaps in our knowledge as to when, how and how much activity is optimal...

D-37 Free Communication/Poster - Pulmonary Disease and Exercise

The positive association between muscle mass and bone mass is well known. However, muscle mass and areal bone mineral density are surrogate measures of the more important constructs of muscle function, muscle cross-sectional area (MCSA), and bone strength (as posited in the Mechanostat Theory). PURPOSE: We examined the relationship between lower body muscle power (a measure of muscle function), MCSA, and tibial bone strength in a healthy cohort of 303 17-year-olds. METHODS: This cross-sectional study was part of the ongoing Iowa Bone Development Study. Using peripheral quantitative computed tomography (pQCT), MCSA (66% tibia, mm2), Polar Moment of Inertia (PMI, 38% and 66% tibia, mm4), and Bone Strength Index (BSI, 4% tibia, g/cm3/mm4) were obtained during a clinical visit. Anthropometric measures (ht in cm, wt in kg) and vertical jump height (cm) were also measured. Vertical jump height and the Sayers equation were used to estimate lower body muscle power (Watts). Spearman correlations were calculated for sex-specific associations between muscle power and bone strength measures. Because MSCA is so involved in the relationship between muscle power and bone strength, mediation analysis was used to examine the effect of muscle power and MSCA on bone strength through several pathways. RESULTS: Muscle power estimates were significantly associated with bending and compression measures of bone strength. Associations were greater for bending strength (PMI 38%, 66%: females r=.70, r=.69 males r=.76, r=76) than compression strength (BSI: females r=.48 males r=.59). Mediation analysis indicated that muscle power had a significant effect on MSCA (p<.0001 at all sites), as well as on bone strength independent of MSCA (p<.0005 at all sites). CONCLUSIONS: These results showed a significant association between muscle power and bone strength even when controlling for MSCA. This is consistent with the premise that quality and use of muscle contribute over-and-above muscle size. More fully elucidating physical activity and bone health dose-response may require conceptualizing muscle power movements as a dimension of physical activity. Supported by The National Institute of Dental and Craniofacial Research (R01-DE12101 and R01-DE09551) and The National Center for Research Resources (UL1-RR024979 and M01-RR00059).

Sustained effects of physical activity on bone health: Iowa Bone Development Study

Studies of youth athletics and interventions have shown some maintenance of bone mineral content (BMC; g) after cessation of training, but less is known about sustained effects of everyday physical activity (PA). Using a prospective cohort, this report examined potential effects of childhood PA on adolescent BMC. Participants (N=156 boys, 170 girls) had exams at ages 5, 13, and 15. Body size and maturity were determined using anthropometry. Moderate-to-vigorous-intensity PA (MVPA) and vigorous-intensity PA (Vigorous PA) were measured using accelerometry. BMC of the spine and hip was measured using dual-energy X-ray absorptiometry. Mixed regression models tested whether PA at age 5 affected BMC at ages 13 and 15 after adjustment for age (year), height (cm), weight (kg), maturity (pre-peak height velocity or post), and activity level (min/day). Analysis was repeated to control for age 5 BMC. On average, boys participated in 59, 52, and 38min of MVPA and 13, 17, and 11min of Vigorous PA at ages 5, 13, and 15, respectively. MVPA (β=0.799) and Vigorous PA (β=1.338) at age 5 predicted later spine BMC (p<0.05). MVPA (β=0.480) at age 5 predicted hip BMC. Girls participated in 47, 33, and 26min of MVPA and 10, 9 and 7min of Vigorous PA at ages 5, 13, and 15, respectively. Neither MVPA nor Vigorous PA predicted later spine BMC. MVPA (β=0.302) at age 5 predicted hip BMC. After controlling for BMC at age 5 as well as the other covariates, the effect of MVPA (β=0.695) and Vigorous PA (β=1.079) at age 5 remained significant for boys at the spine. For girls, neither MVPA nor Vigorous PA at age 5 predicted spine or hip BMC. Children's early PA appears to have a modest effect on adolescent BMC at the critical regions of spine and hip; benefits may be greater for geometric changes, which future studies should include.

Effects of Life-long Fluoride Intake on Bone Measures of Adolescents

Controversy persists concerning the impact of community water fluoridation on bone health in adults, and few studies have assessed relationships with bone at younger ages. Ecological studies of fluoride’s effects showed some increase in bone mineral density of adolescents and young adults in areas with fluoridated water compared with non-fluoridated areas. However, none had individual fluoride exposure measures. To avoid ecological fallacy and reduce bias, we assessed associations of average daily fluoride intake from birth to age 15 yr for Iowa Bone Development Study cohort members with age 15 yr dual-energy x-ray absorptiometry (DXA) bone outcomes (whole body, lumbar spine, and hip), controlling for known determinants (including daily calcium intake, average daily time spent in moderate-to-vigorous intensity physical activity, and physical maturity). Mean (SD) daily fluoride intake was 0.66 mg (0.24) for females and 0.78 mg (0.30) for males. We found no significant relationships between daily fluoride intake and adolescents’ bone measures in adjusted models (for 183 females, all p values ≥ .10 and all partial R2 ≤ 0.02; for 175 males, all p values ≥ .34 and all partial R2 ≤ 0.01). The findings suggest that fluoride exposures at the typical levels for most US adolescents in fluoridated areas do not have significant effects on bone mineral measures.

Ten-year objective physical activity tracking: Iowa Bone Development Study.

This study aimed to examine the tracking of physical activity (PA) during a 10-yr period and to investigate whether sex differences in PA trajectories are altered after aligning by maturity instead of age. The Iowa Bone Development Study collected accelerometer data on a cohort of 140 girls and 128 boys at ages 5, 9, 11, 13, and 15 yr. Logistic regression determined the odds ratio of being in lowest PA tertile at 15 yr if in lowest tertile at age 5 yr. Spearman correlation coefficients examined PA tracking from age 5 to 15 yr. Using additional Iowa Bone Development participants at ages 9, 11, 13, and 15 yr (N = 482, 457, 416, and 316, respectively), we examined the stability of PA for chronological and biological age in 2-yr intervals surrounding peak height velocity (PHV) age. Year from PHV was estimated using the Mirwald prediction equation. Girls had significant 10-yr correlations (r = 0.27); boys did not. Girls, not boys, were more likely to be in the lowest tertile for PA at age 15 yr if in the lowest tertile at age 5 yr (moderate to vigorous PA: odds ratio = 3.1, 95% confidence interval = 1.4-6.9; vigorous PA: odds ratio = 2.8, 95% confidence interval = 1.2-6.1). Girls' 2-yr intervals for PA showed moderate associations (r = 0.31-0.56) when aligned chronologically but were moderate to high (r = 0.41-0.63) when aligned biologically. Boys' associations were low to moderate (r = 0.26-0.56) chronologically. When aligned biologically, the associations were low for the -1- to 1-yr interval (1 yr before the 1-yr post-PHV) but moderate to high for the -2- to 0-yr and 0- to 2-yr intervals (r = 0.50-0.61). Physical activity tracking from childhood to adolescence is stronger in girls than that in boys. Intervention programs targeting boys should focus on time surrounding puberty in boys during which activity patterns change.

Which contributes more to childhood adiposity-high levels of sedentarism or low levels of moderate-through-vigorous physical activity? The Iowa Bone Development Study.

To examine the relative importance of sedentarism and moderate-to-vigorous physical activity for adiposity development in children and adolescents. A total of 277 boys and 277 girls (95% white; two-thirds of parents with college graduation or higher education) from the Iowa Bone Development Cohort Study completed body fat and accelerometry measurement at examinations of 8, 11, 13, and/or 15 years of age (during 2000-2009). The main exposure was accelerometry-measured sedentary time, frequency of breaks in sedentary time, and moderate- to vigorous-intensity physical activity time. The outcome was dual energy x-ray absorptiometry-measured body fat mass. Adjusted for age, height, physical maturity, and sedentary time, growth models showed that high moderate-to-vigorous physical activity time was associated with low body fat mass in both boys (coefficient β=-0.10±0.02) and girls (β=-0.05±0.01; P<.01). However, sedentary time and frequency of breaks in sedentary time were not associated with body fat mass. This study does not support an independent effect of sedentarism on adiposity. The preventive effect of moderate- to vigorous-intensity physical activity on adiposity in children and adolescents remained strong after adjusting for the effect of sedentarism.

Breaks in Sedentary Time during Childhood and Adolescence

The frequency of interruptions in sedentary time (sedentary breaks) is an aspect of sedentary behaviors that may be associated with metabolic health outcomes. The aim of this study was to describe the change in the frequency of sedentary breaks during a 10-yr period from ages 5 to 15 yr. The longitudinal Iowa Bone Development Study has collected accelerometry data at approximately 5, 8, 11, 13, and 15 yr. Data from participants who wore an accelerometer at least 10 h·d(-1) and 3 d per data collection episode were used (423 children at age 5 yr, 550 children at age 8 yr, 520 children at age 11 yr, 454 children at age 13 yr, and 344 children at age 15 yr). The frequency of sedentary breaks was determined based on accelerometry data and compared by weekday/weekend, period during the day, gender, and data collection episode. The frequency of sedentary breaks decreased by >200 times per day during a 10-yr period from ages 5 to 15 yr. Linear regression models estimated a 1.84-times-per-hour decrease per year for boys and a 2.04-times-per-hour decrease per year for girls (P values < 0.0001). Both boys and girls showed significantly fewer breaks on weekdays from morning to 3:00 p.m. than on weekends from morning to 3:00 p.m. (P values < 0.0001). The frequency of sedentary breaks was slightly higher among boys than among girls (gender difference ≤ 2 times per hour; P values < 0.01 at ages 11, 13, and 15 yr). Breaks in sedentary time notably decrease during childhood and adolescence. During school hours, boys and girls have fewer breaks in sedentary time than during any other period of weekday or weekend day.

Tracking of accelerometry-measured physical activity during childhood: ICAD pooled analysis

BackgroundUnderstanding of physical activity (PA) tracking during childhood is important to predict PA behaviors and design appropriate interventions. We compared tracking of PA according to PA level and type of day (weekday/weekend) in a pool of five children’s cohort studies.MethodsData from ALSPAC, CLAN, Iowa Bone Development Study, HEAPS, PEACH were extracted from the International Children’s Accelerometry Database (ICAD), resulting in 5,016 participants with age, gender, and accelerometry data at both baseline and follow-up (mean age: 10.3 years at baseline, 12.5 years at follow-up). Daily minutes spent in moderate- and vigorous-intensity PA (MVPA) and vigorous-intensity PA (VPA) was categorized into quintiles. Multinomial logistic regression models were fit to predict follow-up (M)VPA from baseline (M)VPA (reference: 20- < 80%tile), age at follow-up, and follow-up duration.ResultsFor the weekday, VPA tracking for boys with high baseline VPA was higher than boys with low baseline VPA (ORs: 3.9 [95% CI: 3.1, 5.0] vs. 2.1 [95% CI: 1.6, 2.6]). Among girls, high VPA was less stable when compared low VPA (ORs: 1.8 [95% CI: 1.4, 2.2] vs. 2.6 [95% CI: 2.1, 3.2]). The pattern was similar for MVPA among girls (ORs: 1.6 [95% CI: 1.2, 2.0] vs. 2.8 [95% CI: 2.3, 3.6]). Overall, tracking was lower for the weekend.ConclusionsPA tracking was higher on the weekday than the weekend, and among inactive girls than active girls. The PA “routine” of weekdays should be used to help children establish healthy PA patterns. Supports for PA increase and maintenance of girls are needed.

Predictability of TV Viewing Throughout Childhood: Iowa Bone Development Study

PURPOSE: Tracking studies determine the stability and predictability of specific phenomena. This study examined tracking of TV viewing (TV) from middle childhood through early adolescence after adjusting for moderate and vigorous physical activity (MVPA), percentage of body fat (% BF), and maturity. METHODS: TV was measured at ages 5, 8, 11, and 13 yr (n = 434) via parental- and self-report in a population-based cohort. MVPA was measured using the Actigraph, % BF using dual-energy x-ray absorptiometry, and maturity via Mirwald predictive equations. Generalized Estimating Equations (GEE) were used to assess stability and logistic regression was used to predict children "at risk" for maintaining excessive TV (> 2 hr). Additional models examined tracking in overfat children (boys ≥ 25% BF; girls ≥ 32% BF combined). RESULTS: More than half of the sample reported more than 2 hrs of TV daily at each measurement age. The crude GEE coefficients were 0.35 (95% CI = 0.26, 0.44) for boys, 0.34 (0.26, 0.43) for girls, and 0.41 (0.23, 0.59) for overfat. The GEE, adjusted for MVPA, % BF, and maturity, were 0.35 (0.26, 0.44) for boys and 0.32 (0.23, 0.40) for girls. The GEE, adjusted for MVPA, maturity, and gender, in the overfat (boys and girls combined) was 0.45 (0.27, 0.64). Gender (being female) was significant in this model. The adjusted OR were 3.2 (2.0, 5.2) for boys, 2.9 (1.9, 4.6) for girls, and 6.2 (2.2, 17.2) for overfat. That is, boys and girls were 3 times as likely to watch excessive TV later in life if they were excessive TV watchers at age 5 yr. For those overfat at age 5 yr (especially girls), the odds were much higher (6 times as likely). CONCLUSION: TV is moderately stable throughout childhood and predictive of later viewing behavior. It appears to be entrenched in younger children, especially overfat, young girls. Adjusting for MVPA did not significantly alter results suggesting that PA and sedentarism are distinct behaviors. Since habitual patterns of excessive TV in young children tended to continue into adolescence, tailored, early intervention strategies may be warranted to prevent excessive TV before it begins. Supported by the National Institute of Dental and Craniofacial Research (R01-DE12101, R01-DE09551); General Clinical Research Centers Program (M01-RR00059); National Center for Research Resources (UL1 RR024979).

Association Between Light-Intensity Physical Activity and Adiposity in Childhood

The purpose of this study was to examine whether the association between daily light-intensity physical activity (LPA) and total body fat mass changes during childhood. The study sample was 577 children participating in the longitudinal Iowa Bone Development Study. Body fat mass and physical activity (PA) were measured using dual energy X-ray absorptiometry (DXA) and accelerometers, respectively, at approximately 5, 8, and 11 years of age. Age- and gender-specific multivariable linear regression models were fit to predict fat mass by LPA, adjusted for actual age, birth weight, fat-free mass, height, moderate- to vigorous-intensity PA, and physical maturity (only for girls). Among boys, LPA was negatively associated with fat mass at age 11, but not age 5 or 8. Among girls, LPA was negatively associated with fat mass at ages 8 and 11, but not at age 5. LPA may have a beneficial effect against excess adiposity among older children.

Effects of Adiposity on Physical Activity in Childhood

The aim of this study was to examine whether adiposity level is associated with subsequent physical activity (PA) level in childhood. Study participants were 326 children participating in the Iowa Bone Development Study. PA and fat mass were measured using accelerometers and dual-energy x-ray absorptiometry (DXA) at approximately 5, 8, and 11 yr. Data for relevant variables such as parents' education and PA levels and family income were also collected. Gender-specific generalized linear models were fit to examine the association between percentage body fat (%BF) at age 8 and intensity-weighted moderate- to vigorous-intensity PA (IW-MVPA) at age 11. After adjusting for IW-MVPA at age 8, the interval between the age 8 and 11 examinations, residualized change scores of %BF and IW-MVPA from age 5 to 8, and mother's education level, %BF at age 8 was negatively associated with IW-MVPA at age 11 among boys (P < 0.05). After adjusting for IW-MVPA at age 8, physical maturity, and family income, %BF at age 8 was negatively associated with IW-MVPA at age 11 among girls (P < 0.05). Categorical data analysis also showed that the odds ratio (OR) of being in the lowest quartile relative to the highest quartile of IW-MVPA at age 11 for boys and girls with high %BF at age 8 were approximately four times higher than the OR for those with low %BF at age 8 (OR = 4.38, 95% CI = 1.05-18.24 for boys; OR = 4.48, 95% CI = 1.35-14.85 for girls). This study suggests that adiposity level may be a determinant of PA behavior. Specific intervention strategies for overweight children may be needed to promote PA.

Tracking of TV and video gaming during childhood: Iowa Bone Development Study.

BackgroundTracking studies determine the stability and predictability of specific phenomena. This study examined tracking of TV viewing (TV) and video game use (VG) from middle childhood through early adolescence after adjusting for moderate and vigorous physical activity (MVPA), percentage of body fat (% BF), and maturity.MethodsTV viewing and VG use were measured at ages 5, 8, 11, and 13 (n = 434) via parental- and self-report. MVPA was measured using the Actigraph, % BF using dual-energy x-ray absorptiometry, and maturity via Mirwald predictive equations. Generalized Estimating Equations (GEE) were used to assess stability and logistic regression was used to predict children "at risk" for maintaining sedentary behaviors. Additional models examined tracking only in overfat children (boys ≥ 25% BF; girls ≥ 32% BF). Data were collected from 1998 to 2007 and analyzed in 2010.ResultsThe adjusted stability coefficients (GEE) for TV viewing were 0.35 (95% CI = 0.26, 0.44) for boys, 0.32 (0.23, 0.40) for girls, and 0.45 (0.27, 0.64) for overfat. For VG use, the adjusted stability coefficients were 0.14 (0.05, 0.24) for boys, 0.24 (0.10, 0.38) for girls, and 0.29 (0.08, 0.50) for overfat. The adjusted odds ratios (OR) for TV viewing were 3.2 (2.0, 5.2) for boys, 2.9 (1.9, 4.6) for girls, and 6.2 (2.2, 17.2) for overfat. For VG use, the OR were 1.8 (1.1, 3.1) for boys, 3.5 (2.1, 5.8) for girls, and 1.9 (0.6, 6.1) for overfat.ConclusionsTV viewing and VG use are moderately stable throughout childhood and predictive of later behavior. TV viewing appears to be more stable in younger children than VG use and more predictive of later behavior. Since habitual patterns of sedentarism in young children tend to continue to adolescence, early intervention strategies, particularly to reduce TV viewing, are warranted.

A Hip Analysis Protocol for Pediatric Bone Densitometry: The Iowa Bone Development Study

Pediatric proximal femur dual-energy X-ray absorptiometry (DXA) scans present analytic challenges because of the lack of standard points of reference in the growing skeleton. The Iowa Bone Development Study (IBDS) developed a modified pediatric-specific proximal femur analysis protocol using Hologic software. Serial DXA measurements were obtained for 214 children at approximate ages 5, 8, 11, and 13 yr. Standard analysis procedures as described by the manufacturer (Hologic default) were compared with the IBDS protocol. The IBDS protocol yielded lower but more stable results for bone area, bone mineral content (BMC), and bone mineral density for total hip, femoral neck, trochanter, and intertrochanter as a result of more precisely controlling the regions of interest. Linear regression models with body size, age, and gender as predictors were developed to examine variation in measurements. Coefficients of determination ( R 2) with the IBDS protocol were greater for each time point, demonstrating that the modified protocol was better aligned with body size. Similarly, Spearman correlation coefficients between total hip and hip subregions were consistently higher for BMC and bone area with the IBDS protocol with differences more notable among younger children. The IBDS protocol provides a reproducible method for evaluating pediatric proximal femur DXA scans during growth.

Early physical activity provides sustained bone health benefits later in childhood.

This study examined the potential effect of early childhood moderate and vigorous physical activity (MVPA) on later bone health. Three hundred and thirty-three children, participating in the Iowa Bone Development Study, were studied at ages 5, 8, and 11 yr. MVPA (min x d(-1)) was measured using an accelerometry-based physical activity monitor. Bone mineral content (BMC; g) of the whole body, lumbar spine, and hip was measured using dual-energy x-ray absorptiometry. Mixed regression models were used to test whether MVPA at age 5 yr had an effect on BMC at ages 8 and 11 yr after adjustment for concurrent height, weight, age, maturity, and MVPA. The analysis was repeated to control for bone outcomes at age 5 yr. Mixed-model least-squares mean values at the person level of covariates for age group were used to compare the BMC at ages 8 and 11 yr of children in the highest and lowest quartiles of MVPA at age 5 yr. For boys and girls, MVPA at age 5 yr predicted BMC adjusted for concurrent height, weight, age, maturity, and MVPA at ages 8 and 11 yr (P < 0.05). When the analysis was repeated to also control for BMC at age 5 yr, the effect of MVPA at age 5 yr was significant for boys but not for girls. Boys and girls in the highest quartile of MVPA at age 5 yr had 4%-14% more BMC at ages 8 and 11 yr than those in the lowest quartile of MVPA at age 5 yr (P < 0.05). These results provide support for the benefits of early MVPA on sustained bone health during childhood especially for boys. Results indicate the importance of increasing MVPA as a strategy to improve BMC later in childhood.

Eight Year Longitudinal Results from the Iowa Bone Development Study: Activity and Video Gaming Predict Fat Mass Throughout Childhood

PURPOSE: Childhood obesity has multiple causes; however, physical activity (PA) is likely to provide a protective effect. Using a longitudinal observational design spanning 8 years of growth (age 5 to 13), we examined associations between PA and fat mass (FM) in a cohort of healthy children (n=398). METHODS: A total of 188 boys and 210 girls participating in the Iowa Bone Development Study were assessed at least twice in 8 years. PA was measured by the Actigaph physical activity monitor and FM was assessed by dual x-ray absorptiometry (DXA). Data were analyzed using multilevel (random- and fixed-effects) regression models with adjustment for centered age (yr), centered age-squared (yr), height (cm), somatic maturity (0,1), TV viewing (1-5 scale), video gaming (1-5 scale). Quadratic age was included to allow for non-linear growth. Maturity was estimated using predictive equations by Mirwald (maturity offset). TV viewing and video gaming, markers of sedentary activity, were estimated from parent and child reports. The first-level of the models described the child-specific developmental change of FM over the course of the study (random effect). The predictor variables were added in a stepwise fashion as fixed effects to the second-level of the models. Likelihood ratio statistics were used to determine whether the effects of predictor variables were significant contributors to the models. All models were gender-specific and p < 0.05. RESULTS: Throughout childhood, boys and girls who were the most active had the least amount of FM (inverse association). Beta coefficients indicated that if all other variables were held constant, 10 min of PA would result, on average, in.25 kg less FM. In addition, video gaming; but not TV viewing, was positively associated with FM. CONCLUSION: These results provide evidence that greater amounts of everyday PA are associated with a healthy developmental profile for adiposity; whereas video gaming increases the likelihood of excessive adiposity. Increasing the level of PA is likely to be a safe and efficient strategy to counter obesity in children. Supported by NIH Grants R01-DE 12101 and R01-DE09551.

Sustained Effect of Early Physical Activity on Body Fat Mass in Older Children

Physical activity is assumed to reduce excessive fatness in children. This study examined whether the benefits of early childhood moderate-to-vigorous physical activity (MVPA) on fatness are sustained throughout childhood. MVPA minutes per day (min/d) and fat mass (kilograms; kg) were measured using accelerometry and dual-energy x-ray absorptiometry in 333 children aged 5, 8, and 11 years who were participating in the Iowa Bone Development Study. Mixed regression models were used to test whether MVPA at age 5 years had an effect on fat mass at age 8 years and age 11 years, after adjustment for concurrent height, weight, age, maturity, and MVPA. The analysis was repeated to control for fat mass at age 5 years. Using mixed-model least-squares means, adjusted means of fat mass at age 8 years and age 11 years were compared between the highest and lowest quartiles of MVPA at age 5 years. Data were collected between 1998 and 2006 and analyzed in 2008. For boys and girls, MVPA at age 5 years was a predictor of adjusted fat mass at age 8 years and age 11 years (p<0.05). In girls, the effect of MVPA at age 5 years was not significant when fat mass at age 5 years was included. Boys and girls in the highest quartile of MVPA at age 5 years had a lower fat mass at age 8 years and age 11 years than children in the lowest MVPA quartile at age 5 years (p<0.05; mean difference 0.85 kg at age 8 years and 1.55 kg at age 11 years). Some effects of early-childhood MVPA on fatness appear to persist throughout childhood. Results indicate the potential importance of increasing MVPA in young children as a strategy to reduce later fat gains.

Subjective and objective measures of physical activity in relationship to bone mineral content during late childhood: the Iowa Bone Development Study

Subjective and objective measures of physical activity in relationship to bone mineral content during late childhood: the Iowa Bone Development Study