Are field measures of adiposity sufficient to establish fatness-related linkages with metabolic outcomes in adolescents?

OBJECTIVE: To examine the associations between the adiposity-related information conveyed by field fatness measures: body mass index (BMI), waist circumference (WC) and sum of triceps and subscapular skinfolds (SUM SF) relative to dual-energy X-ray absorptiometry (DXA), beyond their common intercorrelations, with three important metabolic variables in US adolescents. METHODS: We analyzed data on adiposity and insulin resistance (HOMA-IR), serum triglycerides (TGs) and total cholesterol (TC) from three US national surveys. In two-stage least-square modeling, we first calculated the common adiposity variance, and then used multivariate linear and quantile regressions to access residual associations with each measure. RESULTS: Basic associations for each of the adiposity measures were similar but differences emerged in residual adiposity analyses scaled by s.d. units. While a 1 s.d. change in residual variance in DXA total fat beyond that accounted for by BMI (DXA|BMI) was strongly and significantly associated with all outcomes, associations with DXA accounting for SUM SF (DXA|SUM SF) and WC (DXA|WC) were weak or nonsignificant. Contrasted amongst themselves, the residual score association between BMI|SUM SF (ß=0.06, P<0.0001) and HOMA-IR was weaker, and half as strong as that for the converse, SUM SF|BMI (ß=0.13, P=0.020). SUM SF|WC was stronger than WC|SUM SF (ß=0.08, P<0.0001 vs SUM SF|WC ß=0.13, P<0.0001). Associations were similar for TGs and TC. CONCLUSIONS: Laboratory methods like DXA offer minimal explanatory advantage over field methods in assessing adiposity-related contributions to metabolic outcomes in adolescents. Among the simple fatness measures, skinfolds convey additional information beyond BMI and WC when estimating associations both at the population mean and at the upper extremes of metabolic factors.

Comparability of skinfold thickness to DXA whole-body total fat in their associations with serum triglycerides in youths.

OBJECTIVE: To determine the comparability of triceps and subscapular skinfold thicknesses with dual X-ray absorptiometry (DXA) whole-body total fat (kg) in relation to serum triglyceride (TG) levels and increased risk of elevated TG levels, and identified optimum skinfold cutoffs for screening purposes in US adolescents. SUBJECTS/METHODS: Data from triceps and subscapular skinfold thickness, DXA whole-body total fat and serum TGs were obtained from 1505 US adolescents ages 12.00-17.99 years, who participated in two continuous National Health and Nutrition Examination Survey (NHANES) cycles 2001-2004. Study associations were examined with linear and logistic models, and ROC (receiver operating characteristic) analyses were used to derive skinfold cutoffs for identifying the risk of elevated TG levels. RESULTS: Using area under the curves (AUCs) as metrics of prediction accuracy (with bootstrapped 95% CIs), no significant differences were found between skinfolds and DXA logistic models for predicting elevated TG levels. Similarly, skinfold and DXA models had comparable precision in predicting continuous serum TG from bootstrapped root mean squared errors for both sexes. Population-adjusted marginal mean estimates indicated that youths whose skinfolds are in the top quartile had TG levels within 83-108 mg/dl. Skinfold cutoffs for predicting elevated estimated TG using ROC analyses showed that cutoffs decreased with age and ranged from 13 to 30 mm for ages 12-17, in yearly intervals. CONCLUSION: Skinfold thicknesses were comparable to DXA whole-body total fat in predicting serum TG levels. These skinfold cutoffs could be used in practical settings as a first pass screener for identifying US adolescents at risk of elevated serum TGs.

A two-part model for reference curve estimation subject to a limit of detection.

Reference curves are commonly used to identify individuals with extreme values of clinically relevant variables or stages of progression which depend naturally on age or maturation. Estimation of reference curves can be complicated by a technical limit of detection (LOD) that censors the measurement from the left, as is the case in our study of reproductive hormone levels in boys around the time of the onset of puberty. We discuss issues with common approaches to the LOD problem in the context of our pubertal hormone study, and propose a two-part model that addresses these issues. One part of the proposed model specifies the probability of a measurement exceeding the LOD as a function of age. The other part of the model specifies the conditional distribution of a measurement given that it exceeds the LOD, again as a function of age. Information from the two parts can be combined to estimate the identifiable portion (i.e. above the LOD) of a reference curve and to calculate the relative standing of a given measurement above the LOD. Unlike some common approaches to LOD problems, the two-part model is free of untestable assumptions involving unobservable quantities, flexible for modeling the observable data, and easy to implement with existing software. The method is illustrated with hormone data from the Third National Health and Nutrition Examination Survey.

Otitis media and associations with overweight status in toddlers.

INTRODUCTION: Otitis media (OM) is a significant disease that affects nearly all children early in life. Recently, childhood overweight has become an epidemic. Past research has demonstrated that a history of OM is related to food preferences and overweight through proposed physiological mechanisms. The purpose of this study was to explore the relationship between recurrent OM (ROM)/tympanostomy tube treatment and overweight status. METHODS: Data were analyzed from a prospective cohort of mothers and children recruited from 1991-1996 from a local health maintenance organization. ROM and tympanostomy tube status were obtained through a combination of physical exam and medical record abstraction. ROM and tympanostomy tube status were analyzed as categorical variables with weight-for-length (WFL) data from well child checks. Chi-square and logistic regression for univariate and multivariate analyses were performed. RESULTS: 11.4% of children had a WFL measure at two years of age ≥ 95 th percentile. Those children with a history of tympanostomy tube treatment had a significantly increased risk of having a WFL ≥ 95 th percentile after controlling for birth weight, maternal prenatal smoking, maternal education, and family income (OR 3.32, 95% CI 1.43-7.72). The alternative hypothesis that children with larger WFL at two month of age would have a greater number of OM episodes by two years of age was not significant. CONCLUSION: The findings of this study are consistent with the hypothesis and prior research that OM treated with tympanostomy tubes is associated with overweight status.

Association of inflammation with worsening HOMA-insulin resistance.

AIMS/HYPOTHESIS: We examined the cross-sectional and longitudinal relationships between C-reactive protein (CRP), a marker of low-grade inflammation, and insulin resistance and whether the association was independent of obesity and oxidative stress. METHODS: CRP and insulin resistance (homeostasis model assessment of insulin resistance [HOMA-IR]) data were obtained in a population-based, prospective observational study, Coronary Artery Risk Development in Young Adults (CARDIA), during 1992-2006. RESULTS: CRP showed a significant positive association with insulin resistance, both cross-sectionally and longitudinally (5 year follow-up). The estimated increment in HOMA-IR was 0.34 log(e)(pmol/l x [mmol/l]/156.25) (p value for trend <0.0001) in the highest vs lowest CRP quartiles in cross-sectional analysis, whereas the corresponding estimate was 0.12 (p trend <0.0001) in the highest vs lowest CRP quartiles longitudinally over 5 years. The gradient of HOMA-IR across CRP was attenuated but remained statistically significant after controlling for body fat measurements (0.06 in the highest vs lowest CRP in both cross-sectional [p value for trend = 0.001] and longitudinal analyses [p value for trend = 0.01]), and was little changed by further adjustment for oxidative stress markers (F(2)-isoprostanes and oxidised LDL). There were consistent increments in the levels of HOMA-IR with increasing concentrations of CRP over time. In contrast, higher HOMA-IR did not predict future increases in CRP. Findings were similar using fibrinogen as the predictor variable. CONCLUSIONS/INTERPRETATION: Although a substantial portion of this association was explained by obesity, CRP was independently related to concurrent and future insulin resistance.

Growth and endocrine function in patients with Hurler syndrome after hematopoietic stem cell transplantation.

Short stature is characteristic of Hurler syndrome, or mucopolysaccharidosis type IH (MPS IH). Hematopoietic stem cell transplantation (HSCT) is used to treat children with MPS IH. While HSCT corrects some of the metabolic features of MPS IH, its effects on growth are not well delineated. We investigated growth in patients with MPS IH after HSCT and described accompanying endocrine abnormalities. A cohort of 48 patients with MPS IH who had received HSCT between 1983 and 2005 were included. The prevalence of short stature (height <-2 s.d. score, SDS) before HSCT was 9%, and increased to 71% at last follow-up (6.9+/-5.1 years after HSCT). Short stature was positively associated with increased age at HSCT (P=0.002) and TBI (P=0.009). In total, 23% had growth hormone deficiency and/or low insulin-like growth factor-1, one female patient had premature adrenarche, one precocious puberty and 27% had clinical or subclinical hypothyroidism. Growth failure is highly prevalent in children with MPS IH after HSCT. Children who had no TBI exposure and were younger at the time of HSCT had a better height outcome.

A randomized trial of a brief intervention to increase fruit and vegetable intake: a replication study among callers to the CIS.

BACKGROUND: Results are reported from a large randomized trial designed to increase fruit and vegetable consumption among callers to the National Cancer Institute's Cancer Information Service (CIS) (n = 1,717). METHODS: CIS callers assigned to the intervention group (n = 861) received a brief proactive educational intervention over the telephone at the end of usual service, with two follow-up mailouts. Key educational messages and print material derived from the NCI 5 A Day for Better Health program were provided to intervention participants. Participants were interviewed by telephone at 4 weeks (n = 1,307), 4 months (n = 1,180), and 12 months for follow-up (n = 1,016). RESULTS: Results obtained from a single-item measure of fruit and vegetable consumption indicate a significant intervention effect of 0.88 servings per day at 4 weeks follow-up (P < 0.001), 0.63 servings per day at 4 months follow-up (P < 0.001), and 0.43 servings per day at 12 months follow-up (P < 0.001). Using a 7-item food frequency measure, an intervention effect of 0.63 servings per day was obtained at 4 weeks follow-up (P < 0.001), compared with 0.39 servings per day at 4 months follow-up (P = 0.002) and 0.44 servings per day at 12 months follow-up (P = 0.002). A 24-h recall assessment included in the 4-month interviews also yielded a significant intervention effect of 0.67 servings per day (P = 0.015). The vast majority of callers (90%) endorsed the strategy of providing 5 A Day information proactively within the CIS. CONCLUSIONS: This brief educational intervention was associated with higher levels of self-reported fruit and vegetable intake at both short- and long-term follow-up. Additional research is recommended to test this or a similar intervention in diverse populations.

Reliability and validity of parental measurements of infant size.

This study evaluates the reliability and validity of parental measurements of infant size, using illustrated instructions and simple measuring tools. Following pilot tests, final methods were evaluated on a sample of 28 parents (26 mothers and 2 fathers) of infants from 1 to 6 weeks of age. Parents independently measured twice the infant's head circumference (HC), mid-upper arm circumference (MUAC), abdominal circumference (AC), and recumbent length (RL). Infants were also measured twice by a trained observer. Mean parental measures were correlated (intraclass R) with the observer criterion measures at the levels of 0.81 for RL, 0.70 for AC, 0.80 for MUAC, and 0.94 for HC. Relative differences in the means for measurements obtained by parents and the trained observer were small, ranging from 0.3% for HC and RL, to 3.8% for AC. Intraclass correlations of reliability between the two parental measurements ranged from R = 0.84 for MUAC to 0.96 for RL. Given the reliability and validity of the results, the methods tested yield measurements that are suitable for ranking individuals and for use in group-level analyses, and at least in the case of head circumference, for individual-level analyses.

Validity and reliability of self-reported stature and weight of US adolescents.

Validity and reliability of self-reported stature and weight were investigated for U.S. adolescents (12.0-17.0 years) who were participants in the Third National Health and Nutrition Examination Survey (NHANES III). Data were collected on 1,635 youth and were statistically weighted to represent the national population. Self-reported weights are missing from 40% of 12 year olds and 25% of 13 year olds. Those who refused or were unable to provide self-reported weights were younger, shorter, and lighter than those who did. Among those who provided self-reports, the average bias and random error in reporting were largest for the youngest youth. Biases in reporting stature and weight were consistently negative following the NHANES III protocol. The intraclass coefficients between measured and self-reported dimensions within age and gender groups ranged from 0.57 to 0.91 and from 0.85 to 0.98, for stature and weight, respectively. Self-reported stature and weight are not recommended as proxies for measured dimensions for youth less than 14 years of age.

Associations of periodontal disease with femoral bone mineral density and estrogen replacement therapy: cross-sectional evaluation of US adults from NHANES III.

The objectives of this study were to evaluate the possible association of periodontal disease with (1) femoral bone mineral density (BMD), and (2) estrogen replacement therapy in a large sample of US adults (N= 11,655). The mean clinical attachment loss (CAL) per person was the main outcome variable. Based on the total BMD of the proximal femur and using the WHO diagnostic criteria, subjects were classified as having osteoporosis, osteopenia, or normal BMD. After adjusting for confounders, females with high calculus scores and low BMD had significantly more CAL than females with normal BMD and similar calculus scores (p<0.0001). No association was observed among women with low and intermediate levels of calculus. The greater CAL present among women with low BMD was associated with gingival recession. Patterns of findings were similar but equivocal among men, of whom only 66 were osteoporotic. After adjustment for possible confounders, postmenopausal women who reported having used estrogen replacement therapy presented significantly less mean CAL than those who never used estrogen. These findings indicate that in the presence of high calculus scores, females with osteoporosis are at increased risk for attachment loss and that this risk may be attenuated by the use of estrogen replacement therapy.

Differences and trends in antioxidant dietary intake in smokers and non-smokers, 1980-1992: the Minnesota Heart Survey.

PURPOSE: Differences and secular trends in dietary antioxidant vitamin intake (vitamins E, C, and beta-carotene) in current non-smokers, light smokers, and heavy smokers were examined as part of the Minnesota Heart Survey. METHODS: Three cross-sectional surveys were conducted in adults ages 25-74 years in 1980-82 (N = 1682), 1985-87 (N = 2326), and 1990-92 (N = 2487). Dietary information was obtained from a 24-hour dietary recall. Smoking was assessed through self-report. Intakes were adjusted for age, energy intake, body mass index, education level, and exercise level (vitamins E, C and beta-carotene). RESULTS: Antioxidant vitamin intakes were significantly higher in non-smokers than in light (1-20 cig/day) and heavy smokers (>20 cig/day) when all three survey periods were combined. In men, mean vitamin E intake was 9.2 mg, 8.6 mg, and 7.8 mg for non-smokers, light smokers, and heavy smokers, respectively. Results were similar in men for beta-carotene (non-smokers 1408 microg, light smokers 1287 microg, and heavy smokers 1064 microg), and vitamin C (non-smokers 81 mg, light smokers 67 mg, and heavy smokers 56 mg). Women had results of similar magnitude and direction. From 1980-92, secular trends in men showed non-significant increases from 1980-82 to 1990-92 in beta-carotene (+6.1%), while decreases were observed in vitamins E (-1.1%) and C (-2.6%). In contrast, women had large decreases in all antioxidant vitamin intakes: vitamin E (-13%), vitamin C (-18.6%), and beta-carotene (-16.2%). CONCLUSIONS: Light and heavy smokers had a significantly lower overall mean dietary antioxidant vitamin intake than non-smokers. Over the decade, antioxidant dietary intake remained relatively stable in men and decreased in women in Minneapolis-St. Paul, despite improvements in access to antioxidant rich fruits and vegetables.

Estimation of body fat from anthropometry and bioelectrical impedance in Native American children.

OBJECTIVE: Obesity, as measured by body mass index, is highly prevalent in Native American children, yet there are no valid equations to estimate total body fatness for this population. This study was designed to develop equations to estimate percentage body fat from anthropometry and bioelectrical impedance as a critical part of Pathways, a multi-site study of primary prevention of obesity in Native American children. DESIGN: Percentage fat was estimated from deuterium oxide dilution in 98 Native American children (Pima/Maricopa, Tohono O'odham and White Mountain Apache tribes) between 8 and 11 y of age. The mean fat content (38.4%+/-8. 1%) was calculated assuming the water content of the fat-free body was 76%. Initial independent variables were height, weight, waist circumference, six skinfolds and whole-body resistance and reactance from bioelectrical impedance (BIA). RESULTS: Using all-possible-subsets regressions with the Mallows C (p) criterion, and with age and sex included in each regression model, waist circumference, calf and biceps skinfolds contributed least to the multiple regression analysis. The combination of weight, two skinfolds (any two out of the four best: triceps, suprailiac, subscapular and abdomen) and bioelectrical impedance variables provided excellent predictability. Equations without BIA variables yielded r2 almost as high as those with BIA variables. The recommended equation predicts percentage fat with a root mean square error=3.2% fat and an adjusted r2=0.840. CONCLUSION: The combination of anthropometry and BIA variables can be used to estimate total body fat in field studies of Native American children. The derived equation yields considerably higher percentage fat values than other skinfold equations in children.

Agreement among anthropometric indicators identifying the fattest adolescents.

Agreement was sought among six indicators used to classify youth as obese in 625 white youth, aged 12.0-18.0 y, who participated in the Third National Health and Nutrition Examination Survey. Indicators included body mass index (BMI), triceps and subscapular skinfolds, the sum of four skinfolds, waist circumference and percentage body fat determined by bioelectric impedance analysis (BIA). The fattest youth in each age and gender group were considered those > 80th centile for the indicator. Agreement was determined by kappa coefficients, which provide the chance-adjusted proportion of agreement in the upper quintiles to identify the same youth as the fattest. Kappas among indicators range from 0.57-0.85 for males and from 0.56-0.79 for females. Categorical agreement with the fattest youth by percentage body fat, changes considerably with age for most indicators, suggesting that relationships among indicators change during adolescence. Different indicators may identify different subpopulations as the fattest, arguing for caution in use and interpretation of results from different indicators, and in favour of standardized definitions for obesity in youth.

Prevalence of overweight and obesity in American Indian School children and adolescents in the Aberdeen area: a population study.

OBJECTIVES: This study estimated the prevalences of overweight and obesity in American Indian children and adolescents attending schools in the Aberdeen area Indian Health Service (including SD, ND, IA, NE). METHODS: Stature and weight were measured for 12559 children aged 5-17y and prevalences of overweight and obesity were determined relative to gender and age-specific national reference data for the body mass index (BMI). Those with BMI > 85th percentile were considered overweight and those with BMI > 95th percentile were considered obese. RESULTS: Age-adjusted prevalences of overweight were 39.1% and 38.0% for males and females, respectively, and corresponding age-adjusted prevalences for obesity were 22.0% and 18.0%, respectively. There were few regular changes in prevalences of overweight across ages for either gender, or for obesity in females. Prevalences of obesity in males increased systematically with age and exceed prevalences in females at many ages. CONCLUSIONS: Overweight and obesity based on elevated BMI are highly prevalent among American Indian youth. Even at the youngest school ages, overweight is more than twice as likely as national patterns and obesity is more than three times as prevalent. Primary prevention must begin very early among these children.

Body composition assessment in American Indian children.

Although the high prevalence of obesity in American Indian children was documented in several surveys that used body mass index (BMI, in kg/m2) as the measure, there is limited information on more direct measurements of body adiposity in this population. The present study evaluated body composition in 81 boys (aged 11.2+/-0.6 y) and 75 girls (aged 11.0+/-0.4 y) attending public schools in 6 American Indian communities: White Mountain Apache, Pima, and Tohono O'Odham in Arizona; Oglala Lakota and Sicangu Lakota in South Dakota; and Navajo in New Mexico and Arizona. These communities were participating in the feasibility phase of Pathways, a multicenter intervention for the primary prevention of obesity. Body composition was estimated by using a combination of skinfold thickness and bioelectrical impedance measurements, with a prediction equation validated previously in this same population. The mean BMI was 20.4+/-4.2 for boys and 21.1+/-5.0 for girls. The sum of the triceps plus subscapular skinfold thicknesses averaged 28.6+/-7.0 mm in boys and 34.0+/-8.0 mm in girls. Mean percentage body fat was 35.6+/-6.9 in boys and 38.8+/-8.5 in girls. The results from this study confirmed the high prevalence of excess body fatness in school-age American Indian children and permitted the development of procedures, training, and quality control for measurement of the main outcome variable in the full-scale Pathways study.

Design and statistical analysis for the Pathways study.

We report the design, rationale, and statistical procedures used in Pathways, a randomized, school-based intervention for the primary prevention of obesity in American Indian children. The intervention, which is now being implemented in 7 American Indian communities around the country, includes a health-promotion curriculum, a physical education program, a school meal program, and a family involvement component. Forty-one schools serving American Indian children were randomly assigned to be either intervention or control groups. The intervention will begin in the third grade and continue through the end of the fifth grade. Efficacy of intervention will be assessed by differences in mean percentage body fat, calculated by a prediction equation, between intervention and control schools at the end of the fifth grade. Power computations indicate that the study has power to detect a mean difference of 2.8% in body fat. Data analysis will use intention-to-treat concepts and the mixed linear model. The study will be completed in 2000.

Minimum time intervals for serial measurements of growth in recumbent length or stature of individual children.

A method is presented to estimate minimum time intervals for meaningful measurements of growth in recumbent length or stature on individual children. These intervals are based on the statistical features of growth, and consider the reliability of measurement, expected rates of growth, and variation in attained length or stature. Because of the assumptions used, the intervals should be considered as minima, except in some predictable cases. During the prepubescent period there are no differences in minimum intervals calculated for boys and girls. The intervals are shortest during the rapid growth attending infancy, and increase to 0.39 y (4.7 mo) at 8 y of age in boys and girls, and to 0.43 y (5.2 mo) at 10 y of age in boys. A reference curve of minimum intervals for length and stature during the prepubescent period is presented with an equation for more precise estimation of measurement intervals. To accommodate the pubescent growth spurt and its normal variation in timing, 0.5 y is recommended as the minimum interval during pubescence when the maturational timing of the child is unknown. These minimum measurement intervals should be appropriate for almost all individual children when growth in recumbent length or stature is measured serially.

Racial differences in birthweight for gestational age and infant mortality in extremely-low-risk US populations.

Using national data, we develop and contrast the birth-weight percentiles for gestational age by infants of extremely-low-risk (ELR) White and African-American women and examine racial differences in the proportion of small-for-gestational-age (SGA) births. We then scrutinise racial variations in infant mortality rates of the infants of ELR women. We further compare the infant mortality rates of infants at or below the 10th percentile of birthweight for gestational age of each race group to determine whether infants with similar restricted fetal growth have comparable risks of subsequent mortality. Single live births, 34-42 weeks' gestation, to White and African-American US-resident mothers were selected from the 1990-91 US Linked Live Birth--Infant Death File (n = 4,360,829). Extremely-low-risk mothers were defined as: married, aged 20-34 years, 13+ years of education, multiparae, with average parity for age, adequate prenatal care, vaginal delivery, and no reports of medical risk factors, tobacco use or alcohol use during pregnancy. Marked racial variation in birthweight percentiles by gestational age was evident. Compared with ELR White mothers, the risk of an SGA infant was 2.64 times greater for ELR African-American mothers and the risk of infant mortality was 1.61 times greater. For the ELR group, the infant mortality rates of African-American and White infants at or below the 10th percentile of birthweight for gestational age of their respective maternal race group were essentially identical after controlling for gestational age. In conclusion, race differences in fetal growth patterns remained after controlling for risk status. Efforts to remove racial disparities in infant mortality will need to develop aetiological pathways that can explain why African-Americans have relatively higher rates of preterm birth and higher infant mortality rates among term and non-SGA infants.