Cross-sectional and longitudinal associations between TV viewing and girls' body mass index, overweight status, and percentage of body fat

OBJECTIVE: To assess cross-sectional and longitudinal relations between television (TV) viewing and girls' body mass index (BMI), weight status, and percentage of body fat. STUDY DESIGN: Participants included 169 girls who were measured at ages 7, 9, and 11 years. Height and weight were measured and used to calculate girls' BMI and to classify their weight status. Girls' percentage of body fat was assessed with the use of dual-energy x-ray absorptiometry. Mothers reported the hours per day that girls watched TV on a typical day. RESULTS: No significant cross-sectional associations were identified. Results from longitudinal analyses showed that in comparison to girls who never exceeded the American Academy of Pediatrics TV viewing recommendations (ie, watched 相似文献   

Effect of a novel procedure for limiting motion on body composition and bone estimates by dual-energy X-ray absorptiometry in children

We studied the effect of using the BodyFIX (Medical Intelligence Inc, Schwabmunchen, Germany) to immobilize children during a dual-energy X-ray absorptiometry scan on body composition and bone estimates. Overestimates of soft tissue and bone introduced by the BodyFIX were avoided by using a modified version of the system or were corrected by using mathematical models developed in this study.     

Radiographic vertebral morphology: a diagnostic tool in pediatric osteoporosis

OBJECTIVE: To assess the value of spinal radiographs in determining the significance of reductions in bone mass or density in chronically ill children. STUDY DESIGN: A pediatric scoring method for assessment of osteoporotic vertebral changes, developed on the basis of radiographs of 70 healthy controls and established adult scoring methods, was subsequently used to assess 32 pediatric patients with suspected secondary osteoporosis. Radiographic findings were correlated with bone mineral density (BMD), clinical data, and biochemistry. RESULTS: Thirty-two patients (median age 14.1 years) were included. Assessment of spinal radiographs with the developed scoring method found previously undiagnosed spinal compression deformities in 11 patients (34%) of whom 9 were asymptomatic and 8 had lumbar spine (size-corrected) BMD measurements within +/-2.0 SD of the age- and sex-specific norms. Fracture history and cumulative glucocorticoid (GC) dose did not differ between those with and without compression deformities. CONCLUSIONS: Vertebral compression fractures can be documented in a significant number of chronically ill children and are poorly predicted by single BMD measurements and clinical history. Assessment of vertebral morphology is recommended as an additional tool in the diagnostic workup of pediatric osteoporosis.     

Waist circumference is an independent predictor of insulin resistance in black and white youths

OBJECTIVES: We examined how well waist circumference (WC) reflects total and abdominal fat and whether WC predicts insulin resistance independent of body mass index (BMI) percentile in youths. STUDY DESIGN: Body composition was measured by dual-energy x-ray absorptiometry and abdominal adiposity by computed tomography. Insulin sensitivity was measured by the hyperinsulinemic-euglycemic clamp. RESULTS: Both BMI percentile and WC were significantly associated (P < .01) with total and abdominal fat and insulin sensitivity. WC remained a significant (P < .01) correlate of total and abdominal fat and insulin sensitivity after controlling for BMI percentile. By contrast, BMI percentile did not remain a significant correlate of visceral fat and markers of insulin resistance after controlling for WC. Without exception, WC explained a greater variance in abdominal fat and metabolic profiles than did BMI percentile. CONCLUSIONS: Our findings suggest that the prediction of health risks associated with obesity in youths is improved by the additional inclusion of WC measure to the BMI percentile. Such observations would reinforce the importance of including WC in the assessment of childhood obesity to identify those at increased metabolic risk due to excess abdominal fat.     

Overdiagnosis of osteoporosis in children due to misinterpretation of dual-energy x-ray absorptiometry (DEXA)

OBJECTIVE: Dual-energy x-ray absorptiometry (DEXA) is increasingly used to evaluate children for osteoporosis. However, the interpretation of pediatric DEXA is complicated by growth and development. Because most DEXA scans are performed on adults, we hypothesized that physicians who interpret DEXA may not be aware of these pediatric issues, potentially leading to misdiagnosis. STUDY DESIGN: Children (n=34, aged 4-17 years) diagnosed with low bone mineral density (BMD) based on a DEXA scan were referred for possible inclusion in a childhood osteoporosis protocol. The referral DEXA scans were analyzed for accuracy. RESULTS: Thirty (88%) of the scans had at least one error in interpretation. The most frequent error (62%) was use of T-score (SD score compared with young adults) to diagnose osteoporosis, which is inappropriate for children. Other errors included use of a reference database that does not consider gender or ethnic differences (21%), incorrect bone map (21%), inattention to short stature (15%), and other measurement or statistical error (12%). After correcting for these errors, 53% had normal BMD, whereas only 26% retained the diagnosis of low BMD. The remaining 21% could not be given a definitive diagnosis. CONCLUSION: In children, the diagnosis of osteoporosis is often due to misinterpretation of a DEXA scan.     

Bone measurements by peripheral quantitative computed tomography (pQCT) in children with cerebral palsy

OBJECTIVE: To use peripheral quantitative computed tomography (pQCT) to determine bone measurements in patients with cerebral palsy (CP) age 3 to 20 years and compare them with control subjects. STUDY DESIGN: A total of 13 (5 male) patients with CP, along with 2 sex- and age-matched controls for each, were included in a mixed-model analysis with matched pairs as random effects for pQCT bone measurements of the 20% distal tibia. RESULTS: Tibia length was similar in the CP and control groups (P = .57). Weight was marginally higher in the control group (P = .06). Cortical bone mineral content (BMC), area, thickness, polar strength-strain index (pSSI), and periosteal and endosteal circumferences were greater in the control group (P < .05 for all). Relationships between bone measurements and weight showed that cortical BMC, area, periosteal circumference, and pSSI were greater at higher weights in the control group (group-by-weight interaction, P < .05 for all). Cortical thickness was greater in the control group and was correlated with weight. Cortical volumetric bone mineral density (vBMD) was greater with higher weights in the CP group (group-by-weight interaction, P = .03). CONCLUSIONS: Bone strength, as indicated by pSSI, is compromised in children with CP due to smaller and thinner bones, not due to lower cortical bone density.     

Decreased bone mineral density with off-label use of tenofovir in children and adolescents infected with human immunodeficiency virus

5 of 6 children infected with human immunodeficiency virus (HIV) receiving Tenofovir disoproxil fumarate (TDF) experienced absolute decreases in bone mineral density (BMD). 2 pre-pubertal subjects experienced >6% BMD decreases. 1 subject was the smallest child and experienced a 27% decrease, necessitating withdrawal of TDF. Subsequently, her BMD recovered. Monitoring of children infected with HIV who require treatment with TDF is warranted.     

Lifestyle factors and the development of bone mass and bone strength in young women

OBJECTIVE: To evaluate the contributions of adolescent calcium intake, oral contraceptive use, and exercise on bone mass and bone strength.Study design Eighty white women participated in 10 years of the Penn State Young Women's Health Study, a longitudinal study of community participants. We measured bone mineral mass (g), density (BMD, g/cm(2)), and body composition from dual energy x-ray absorptiometry and estimated proximal femur section modulus (bone bending strength). Calcium intake was determined from 45 days of prospective food records at regular intervals between the ages of 12 and 22 years. Exercise history and oral contraceptive use were assessed by questionnaire. RESULTS: Daily calcium intakes between the ages of 12 and 22 years ranged from 500 to 1900 mg/d and were not significantly associated with bone gain or bone strength. Oral contraceptive use during adolescence was not correlated with bone or body composition measurements. Femoral neck BMD did not change from 17 to 22 years of age, but section modulus increased 3% (P <.05). Only exercise during adolescence was significantly associated with increased BMD and bone bending strength. CONCLUSIONS: Adolescent lifestyle patterns can influence young adult bone strength. Our data suggest that exercise is the predominant lifestyle determinant of bone strength for this cohort.     

Reproducibility of DXA measurements of bone mineral density and body composition in children

Background  The technique of X-ray-based dual photon absorptiometry (DXA) is frequently used in children for the detection of changes in bone mass or body composition. Such changes can only be considered real if the uncertainties arising from the measurement technique are exceeded. Objective  Our objectives were twofold: (1) to determine the reproducibility of bone mineral density (BMD) measurements in children at the spine and the hip and from the whole body, as well as of whole-body measurements of mineral mass, lean body mass and fat mass in children; and (2) to estimate, from the measured precision, the time interval that needs to elapse before a statistically significant change in a DXA variable can be detected. Materials and methods  The reproducibility of techniques for the measurement of BMD and body composition using DXA was measured in 15 young children (9 girls and 6 boys) and 17 older children (9 girls and 8 boys). Results  Reproducibility was derived from the standard deviation of three repeated measurements of spine BMD, total hip BMD, whole-body BMD (WBBMD), whole-body bone mineral content (WBBMC), lean mass and fat mass. Technique precision was better than 0.01 g cm⁻² for spine BMD and for WBBMD. Hip BMD measurements were slightly less precise, particularly in younger children (0.013 g cm⁻²). For body composition variables, technique precision was 13 g for WBBMC, 201 g for lean body mass and 172 g for fat mass in younger children. Technique precision for older children was 18 g, 251 g and 189 g for the corresponding variables. Predictions showed that the absence of a normal increase in WBBMC in a small-for-age girl could be established after 12 months. For spine BMD, a significant increase should be observable after 6 months for boys over the age of 11 years. For younger boys, more than 12 months has to elapse before anticipated changes can be detected with confidence. Conclusion  The time intervals required to elapse before decisions can be made concerning the significance of observed differences between successive measurements of BMD or body composition in children depend upon the age of the child.     

Speed of sound: relation to geometric characteristics of bone in children, adolescents, and adults

OBJECTIVES: To investigate the relation between volumetric bone mineral density (vBMD) and speed of sound (SOS). STUDY DESIGN: Total and trabecular vBMD were measured by peripheral quantitative computed tomography at the forearm in a population of 216 individuals of a pediatric outpatient clinic. Moreover, SOS was measured by a quantitative ultrasound device (QUS) at the thumb, patella, and os calcis. RESULTS: Linear regression analysis revealed that the prediction of SOS by vBMD is relatively weak (R2 < 0.1). Moreover, body height and measures of bone size have a stronger influence on SOS than vBMD. The influence of bone size on SOS also depends on the location of measurement (highest prediction of SOS by body height at patella with R2 = 0.56). Anthropometric characteristics have a stronger influence on SOS than measures of bone mineral density at the thumb and patella in comparison to os calcis (body height predicts SOS at os calcis, with R2 = 0.03). Conclusions QUS is not a suitable method to assess bone density. If QUS is applied for the assessment of bone development and of bone fracture risk, the measurement should be performed with consideration of anthropometric measurements.