Long-term precision of dual-energy X-ray absorptiometry body composition measurements and association with their covariates.

Few studies have described the long-term repeatability of dual-energy X-ray absorptiometry scans. Even fewer studies have been performed with enough participants to identify possible precision covariates such as sex, age, and body mass index (BMI). Our objective was to investigate the long-term repeatability of both total and subregional body composition measurements and their associations with covariates in a large sample. Two valid whole-body dual-energy X-ray absorptiometry scans were available for 609 participants in the National Health and Nutrition Examination Survey 2000-2002. Participants with scan-quality issues were excluded. Participants varied in race and ethnicity, sex, age (mean 38.8±17.5; range 16-69 yr), and BMI (mean, 26.9±5.2; range 14.1-43.5 kg/m2). The length of time between scans ranged from 3 to 51 days (mean, 18.7±8.4). Precision error estimates for total body measures (bone mineral density, bone mineral content, lean mass, total mass, fat mass, and percent body fat) were calculated as root mean square percent coefficients of variation and standard deviations. The average root mean square percent coefficients of variation and root mean square standard deviations of the precision error for total body variables were 1.12 and 0.01 g/cm2 for bone mineral density, 1.14 and 27.3 g for bone mineral content, 1.97 and 505 g for fat mass, 1.46 and 760 g for lean mass, 1.10 and 858 g for total mass, and 1.80 and 0.59 for percent body fat. In general, only fat and lean masses were impacted by participant and scan qualities (obesity category, sex, the magnitude of the body composition variables, and time between scans). We conclude that long-term precision error values are impacted by BMI, and sex. Our long-term precision error estimates may be more suitable than short-term precision for calculating least significant change and monitoring time intervals.

The abilities of body mass index and skinfold thicknesses to identify children with low or elevated levels of dual-energy X-ray absorptiometry-determined body fatness.

OBJECTIVE: To examine the accuracies of body mass index (BMI) and skinfold thicknesses in classifying the body fatness of 7365 8- to 19-year-old subjects in a national sample. STUDY DESIGN: We used percent body fat determined by dual-energy x-ray absorptiometry (PBFDXA) between 1999 and 2004. Categories of PBFDXA and the skinfold sum (triceps plus subscapular) were constructed so that that numbers of children in each category were similar to the number in each of 5 BMI categories based on the Centers for Disease Control and Prevention growth charts. RESULTS: Approximately 75% of the children and adolescents who had a BMI-for-age ≥ 95th percentile (considered obese) had elevated body fatness, but PBFDXA levels were more variable at lower BMIs. For example, only 41% of the boys who had a BMI < 25th percentile, had a similarly low PBFDXA. The use of the skinfold sum, rather than BMI, slightly improved the identification of elevated levels of body fatness among boys (P = .03), but not among girls (P > .10). A low sum of the triceps and subscapular skinfold thicknesses was a better indicator of low PBFDXA than was a low BMI, but differences were smaller among children with greater levels of body fatness. Among girls who had a PBFDXA above the median, for example, BMI and the skinfold sum were correlated similarly (r = 0.77-0.79) with body fatness. CONCLUSIONS: Both BMI and skinfold thicknesses are fairly accurate in identifying children who have excess body fatness. In contrast, if the goal is to identify children who have low body fatness, skinfold thicknesses would be preferred.

Total body bone area, bone mineral content, and bone mineral density for individuals aged 8 years and over: United States, 1999-2006.

OBJECTIVES: This report presents bone measurement data from total body dual energy x-ray absorptiometry scans for 28,454 persons aged 8 years and over who participated in the 1999-2006 National Health and Nutrition Examination Survey. The sample consisted of 22,667 respondents with valid data, and 5,787 with missing data that were successfully multiply imputed (i.e., not highly variable). Bone area, bone mineral content, and bone mineral density (BMD) are presented for the total body, the total body minus the head (e.g., subtotal), and 10 subregions of the body. METHODS: Means, standard deviations, and selected percentiles were calculated for the total body, total body minus head (subtotal), and 10 body subregions by sex, race and ethnicity, and age. Smoothed mean total body BMD was plotted by age, sex, and race and ethnicity. Multiple regression was used to evaluate differences in mean total body BMD by age, sex, and race and ethnicity. RESULTS: After adjusting for race and ethnicity, total body BMD among those under age 20 was significantly higher in respondents aged 12-19 than in those aged 8-11 in both sexes. Among adults of both sexes, total body BMD in persons aged 20-49 was significantly higher than in those aged 50-79, and significantly lower in persons aged 80 and over than in those aged 50-79, after adjusting for race and ethnicity. After adjusting for age, total body BMD was significantly higher in non-Hispanic black persons than in non-Hispanic white persons, regardless of age or sex. However, the pattern differed by age when Mexican-American persons were compared with non-Hispanic white persons: Age-adjusted total body BMD was significantly lower among Mexican-American males aged 8-19, was similar in Mexican-American females aged 8-19, and was significantly lower in Mexican-American men and women aged 20 and over.

Osteoporosis or low bone mass at the femur neck or lumbar spine in older adults: United States, 2005-2008.

Nine percent of adults over age 50 years had osteoporosis at either the femur neck or lumbar spine and roughly one-half had low bone mass at either of these two skeletal sites. Having osteoporosis raises the risk of experiencing fractures (1,2). The prevalence of osteoporosis or low bone mass at either the femur neck or lumbar spine was not the same as the prevalence of these conditions when the two skeletal sites were considered separately because some individuals had these conditions at one of the skeletal sites but not the other. The prevalence of osteoporosis or low bone mass differed by age, sex, and race and ethnicity. The prevalence was higher in women and increased with age. Differences by race and ethnicity varied depending on sex and skeletal status category, but when compared with non-Hispanic white persons, Mexican-American persons, and persons of other races tended to be at higher risk, and non-Hispanic black persons tended to be at lower risk of either osteoporosis or low bone mass at the femur neck or lumbar spine.

Lumbar spine and proximal femur bone mineral density, bone mineral content, and bone area: United States, 2005-2008.

OBJECTIVE: This report presents bone measurement data from dual-energy X-ray absorptiometry scans of the lumbar spine and proximal femur for persons aged 8 years and over from the National Health and Nutrition Examination Survey (NHANES) 2005-2008. METHODS: Means, standard deviations, and selected percentiles were calculated for the proximal femur and lumbar spine (total and subregions) by sex, race and ethnicity, and age. Smoothed mean total lumbar spine and femur neck bone mineral density (BMD) were plotted by age, sex, and race and ethnicity. Multiple regression was used to test for significant interactions and to calculate mean total lumbar spine and femur neck BMD after adjusting for age, sex, and race and ethnicity. Differences by sex, race and ethnicity, and age were summarized by calculating the percent difference in adjusted means. RESULTS: Among scanned individuals, 11% lacked total lumbar spine data due to invalid data for one or more lumbar vertebrae, and 4% had invalid data for the proximal femur. Non-Hispanic black persons had 6% higher total lumbar spine BMD and 9%-10% higher femur neck BMD than non-Hispanic white persons. Mean total lumbar spine BMD and femur neck BMD did not differ between Mexican-American and non-Hispanic white persons in those under age 20. For those aged 20 and over, Mexican-American persons had 4% lower total lumbar spine BMD but 1% higher femur neck BMD than non-Hispanic white persons. Mean total lumbar spine BMD was 8%-17% higher in females aged 8-15 compared with males of the same age. In the age group 16-49, mean total lumbar spine BMD was similar or slightly higher for females compared with males, but after age 50 it was 60%-15% lower for females compared with males. Mean femur neck BMD was 5%-13% lower for females than males in all age groups except 12-15.

Smoothed percentage body fat percentiles for U.S. children and adolescents, 1999-2004.

BACKGROUND: The high prevalence of obesity (defined by body mass index) among children and adolescents in the United States and elsewhere has prompted increased attention to body fat in childhood and adolescence. OBJECTIVE: This report provides smoothed estimates of major percentiles of percentage body fat for boys and girls aged 8-19 years in the United States. METHODS: Percentage body fat was obtained from whole-body, dual-energy x-ray absorptiometry (DXA) scans conducted during the 1999-2004 National Health and Nutrition Examination Survey. A nonparametric double-kernel method was employed to smooth percentile curves for the DXA data. RESULTS: The pattern of body fat development differs between boys and girls aged 8-19 years. In most age groups, girls have a higher percentage of body fat than boys. Among boys, there is a drop in body fat percentage in early adolescence that is especially pronounced at the higher percentiles. Among girls this pattern is not seen; percentage body fat increases slightly with age. CONCLUSIONS: These results provide a smoothed reference distribution of percentage body fat for U.S. children and adolescents aged 8-19 years.

Multiple imputation of missing dual-energy X-ray absorptiometry data in the National Health and Nutrition Examination Survey.

In 1999, dual-energy x-ray absorptiometry (DXA) scans were added to the National Health and Nutrition Examination Survey (NHANES) to provide information on soft tissue composition and bone mineral content. However, in 1999-2004, DXA data were missing in whole or in part for about 21 per cent of the NHANES participants eligible for the DXA examination; and the missingness is associated with important characteristics such as body mass index and age. To handle this missing-data problem, multiple imputation of the missing DXA data was performed. Several features made the project interesting and challenging statistically, including the relationship between missingness on the DXA measures and the values of other variables; the highly multivariate nature of the variables being imputed; the need to transform the DXA variables during the imputation process; the desire to use a large number of non-DXA predictors, many of which had small amounts of missing data themselves, in the imputation models; the use of lower bounds in the imputation procedure; and relationships between the DXA variables and other variables, which helped both in creating and evaluating the imputations. This paper describes the imputation models, methods, and evaluations for this publicly available data resource and demonstrates properties of the imputations via examples of analyses of the data. The analyses suggest that imputation helps to correct biases that occur in estimates based on the data without imputation, and that it helps to increase the precision of estimates as well. Moreover, multiple imputation usually yields larger estimated standard errors than those obtained with single imputation.

Body composition data for individuals 8 years of age and older: U.S. population, 1999-2004.

OBJECTIVES: This report presents body composition data from whole body dual energy x-ray absorptiometry scans for persons 8 years of age and older who participated in the National Health and Nutrition Examination Survey (NHANES) 1999-2004. Valid total body measurements were obtained on 16,973 individuals. Through the use of multiple imputation, a useable sample of 22,010 individuals was achieved for analysis. Measures for the total body and regions of the body include total mass, fat mass, percentage fat, lean soft tissue (excluding bone mineral content), and fat-free mass (including bone mineral content). METHODS: Means, standard errors, and selected percentiles were calculated for the total body and for regions of the body by sex, race and ethnic, and age population subgroups. Standard errors of the mean were estimated by Taylor Series Linearization, which incorporates sample weights and accounts for the NHANES complex sample design. RESULTS: Females had higher percentage body fat and fat mass than males. After age 11 years, males had higher lean tissue and fat-free mass than females. Percentage body fat was lowest at ages 16-19 years among males and at ages 8-15 years among females. Among males, non-Hispanic white persons had greater fat mass than either Mexican American or non-Hispanic blacks. Among females, non-Hispanic black persons had greater fat mass than either Mexican American or non-Hispanic whites. Mexican-American males and females had less lean soft tissue than either non-Hispanic white or non-Hispanic black males and females. Among both males and females, lean soft tissue and fat-free mass were lowest at ages 8-11 years.

Prevalence of urinary incontinence in men: results from the national health and nutrition examination survey.

PURPOSE: We estimated the prevalence of urinary incontinence in the United States adult male population and identified associated factors. MATERIALS AND METHODS: Data were analyzed for 5,297 men 20 years old or older who participated in the 2005 to 2006 and 2007 to 2008 cycles of the National Health and Nutrition Examination Survey, a cross-sectional, nationally representative survey of the United States noninstitutionalized population. Urinary incontinence (score of 3 or greater on a validated incontinence severity index, indicating moderate to severe leakage) was assessed. Potential associated factors included age, race/ethnicity, education, self-reported health status, prior diagnosis of prostate cancer and/or enlarged prostate (men 40 years old or older), chronic diseases and depression status. Prevalence ORs were estimated from a multivariable logistic regression analysis using appropriate sampling weights. RESULTS: The prevalence of moderate/severe urinary incontinence was 4.5% (95% CI 3.8, 5.4). Prevalence increased with age from 0.7% (95% CI 0.4, 1.6) in men 20 to 34 years old, to 16.0% (95% CI 13.0, 19.4) in men 75 years old or older (p <0.001). We found no difference in prevalence by racial/ethnic group (p = 0.38). Factors significantly associated (p <0.05) with urinary incontinence were age (per 10-year increase, OR 1.8; 95% CI 1.6, 2.0), major depression (OR 2.7; 95% CI 1.6, 4.0) and hypertension (OR 1.3; 95% CI 1.1, 1.5). CONCLUSIONS: Age and race adjusted prevalence estimates for urinary incontinence in men are consistent with other estimates using a similar definition. To our knowledge this is the first study that identifies factors associated with moderate to severe urinary incontinence in men.

High adiposity and high body mass index-for-age in US children and adolescents overall and by race-ethnic group.

BACKGROUND: Body mass index (BMI)-for-age has been recommended as a screening test for excess adiposity in children and adolescents. OBJECTIVE: We quantified the performance of standard categories of BMI-for-age relative to the population prevalence of high adiposity in children and adolescents overall and by race-ethnic group in a nationally representative US population sample by using definitions of high adiposity that are consistent with expert committee recommendations. DESIGN: Percentage body fat in 8821 children and adolescents aged 8-19 y was measured by using dual-energy X-ray absorptiometry in 1999-2004 as part of a health examination survey. RESULTS: With the use of several different cutoffs for percentage fat to define high adiposity, most children with high BMI-for-age (> or = 95th percentile of the growth charts) had high adiposity, and few children with normal BMI-for-age (<85th percentile) had high adiposity. The prevalence of high adiposity in intermediate BMI categories varied from 45% to 15% depending on the cutoff. The prevalence of a high BMI was significantly higher in non-Hispanic black girls than in non-Hispanic white girls, but the prevalence of high adiposity was not significantly different. CONCLUSIONS: Current BMI cutoffs can identify a high prevalence of high adiposity in children with high BMI-for-age and a low prevalence of high adiposity in children with normal BMI-for-age. By these adiposity measures, less than one-half of children with intermediate BMIs-for-age (85th to <95th percentile) have high adiposity. Differences in high BMI ranges between race-ethnic groups do not necessarily indicate differences in high adiposity.

Prevalence and trends in low femur bone density among older US adults: NHANES 2005-2006 compared with NHANES III.

Hip fracture incidence appears to be declining in the United States, but changes in bone mineral density (BMD) of the population have not been evaluated. We used femur BMD data from the National Health and Nutrition Examination Survey (NHANES) 2005-2006 to estimate the prevalence of low femoral BMD in adults age 50 years and older and compared it with estimates from NHANES III (1988-1994). Dual-energy X-ray absorptiometry systems (pencil-beam geometry in NHANES III, fan-beam geometry in NHANES 2005-2006) were used to measure femur BMD, and World Health Organization (WHO) definitions of low BMD were used to categorize skeletal status. In 2005-2006, 49% of older US women had osteopenia and 10% had osteoporosis at the femur neck. In men, 30% had femur neck osteopenia and 2% had femur neck osteoporosis. An estimated 5.3 million older men and women had osteoporosis at the femur neck, and 34.5 million more had osteopenia in 2005-2006. When compared with NHANES III, the age-adjusted prevalence of femur neck osteoporosis in NHANES 2005-2006 was lower in men (by 3 percentage units) and women (by 7 percentage units) overall and among non-Hispanic whites. Changes in body mass index or osteoporosis medication use between surveys did not fully explain the decline in osteoporosis. Owing to the increase in the number of older adults in the US population, however, more older adults had low femur neck BMD (osteoporosis + osteopenia) in 2005-2006 than in 1988-1994. Thus, despite the decline in prevalence, the estimated number of affected older adults in 2005-2006 remained high.

Health disparities among Mexican American women aged 15-44 years: National Health and Nutrition Examination Survey, 1999-2004.

OBJECTIVES: We analyzed the health of Mexican American women aged 15 to 44 years, by generation and language preference, to guide planning for reproductive health services in this growing population. METHODS: We used personal interview and medical examination data from the 1999 to 2004 National Health and Nutrition Examination Surveys. We used SUDAAN for calculating age-adjusted prevalence estimates of demographic and health characteristics. The Satterthwaite adjusted F test and Student t test were used for subgroup comparisons. RESULTS: The women had different health profiles (P < .05) by generation and language preference. Second- and later-generation women and women who used more English were more likely to be sexually active, to have been younger at first intercourse, and to have had more male sexual partners than were first-generation women and women who used more Spanish. Compared with their first-generation counterparts, second- and later-generation women drank more alcohol, were better educated, had higher incomes, and were more likely to have health insurance. Third-generation women were more likely to have delivered a low-birthweight baby than were first-generation women. CONCLUSIONS: Differences by generation and language preference suggest that acculturation should be considered when planning interventions to promote healthy reproductive behaviors among Mexican American women.

Comparisons of percentage body fat, body mass index, waist circumference, and waist-stature ratio in adults.

BACKGROUND: Body mass index (BMI), waist circumference (WC), and the waist-stature ratio (WSR) are considered to be possible proxies for adiposity. OBJECTIVE: The objective was to investigate the relations between BMI, WC, WSR, and percentage body fat (measured by dual-energy X-ray absorptiometry) in adults in a large nationally representative US population sample from the National Health and Nutrition Examination Survey (NHANES). DESIGN: BMI, WC, and WSR were compared with percentage body fat in a sample of 12,901 adults. RESULTS: WC, WSR, and BMI were significantly more correlated with each other than with percentage body fat (P < 0.0001 for all sex-age groups). Percentage body fat tended to be significantly more correlated with WC than with BMI in men but significantly more correlated with BMI than with WC in women (P < 0.0001 except in the oldest age group). WSR tended to be slightly more correlated with percentage body fat than was WC. Percentile values of BMI, WC, and WSR are shown that correspond to percentiles of percentage body fat increments of 5 percentage points. More than 90% of the sample could be categorized to within one category of percentage body fat by each measure. CONCLUSIONS: BMI, WC, and WSR perform similarly as indicators of body fatness and are more closely related to each other than with percentage body fat. These variables may be an inaccurate measure of percentage body fat for an individual, but they correspond fairly well overall with percentage body fat within sex-age groups and distinguish categories of percentage body fat.

Nutrition assessment in the National Health And Nutrition Examination Survey 1999-2002.

The objective of this study is to describe the components of nutrition assessment in the National Health and Nutrition Examination Survey (NHANES) 1999-2002. The study design was a cross-sectional survey with a nationally representative sample of the US population. The survey participants were interviewed and completed a physical examination. From 1999 to 2002, a total of 25,316 people were included in the eligible sample, 21,004 people (83%) were interviewed, and 19,759 people (78% of the eligible sample) were examined. Dietary assessment consisted of a 24-hour dietary recall interview and questions on supplement use, food security, food-program participation, and other behaviors. Nutrition assessment included anthropometric measurements and body-composition assessment. A number of nutrition biochemistries were measured in blood and urine specimens. In addition, an assessment of cardiovascular fitness and questions on physical activity were included. Data are used to estimate population reference distributions and to monitor trends over time. Data have been used to evaluate the adequacy of nutrient intake using the Dietary Reference Intakes, to assist in development of nutrition policies related to obesity, and to evaluate policies such as folic acid fortification. The NHANES contributes to the knowledge and understanding of nutrition and health status in the US population through public-use microdata files for use by researchers in academia, in the private sector, and in government agencies. Continuous data collection will allow the NHANES to provide more timely information for policy development and evaluation.

Health characteristics of U.S. adults by body mass index category: results from NHANES 1999-2002.

OBJECTIVES: We examined self-reported health characteristics, health care utilization, activity patterns, and demographic characteristics of U.S. adults 20 years and over by body mass index (BMI) category. We hypothesized that overweight and obese adults would report fair/poor health more often, report more health provider visits annually, experience more joint pain, report greater limitations in their daily activities, and report more hours of sedentary leisure-time activity than normal-weight adults. METHODS: Self-reported health characteristics of U.S. adults from the National Health and Nutrition Examination Survey (NHANES) 1999-2002 were examined for three BMI categories: normal weight (BMI 18.5-24.9), overweight (BMI 25.0-29.9), and obese (BMI > or = 30.0). Covariates included gender, race/ethnicity, cigarette smoking, and educational attainment. We examined BMI group differences using descriptive and regression methods. RESULTS: Compared to normal-weight individuals, overweight individuals reported fair/poor health more often, more limitations in daily activities, and more health provider contacts. Overweight and obese subjects reported more hours of television watching and video game use compared to normal-weight subjects. CONCLUSION: Our findings are useful to describe the health characteristics of U.S. adults and may be used to anticipate future demand for health services and to support intervention programs that help individuals achieve desirable weight status.

QDR 4500A dual-energy X-ray absorptiometer underestimates fat mass in comparison with criterion methods in adults.

BACKGROUND: Dual-energy X-ray absorptiometry (DXA) has become one of the most frequently used methods for estimating human body composition. Although the DXA technique has been validated for the measurement of fat-free mass and fat mass, differences in calibration between instruments produced by different manufacturers, as well as between different models produced by the same manufacturer, have been reported. OBJECTIVE: The objective was to compare the calibration of the QDR 4500A against criterion methods in a large heterogeneous population. DESIGN: DXA-derived body-composition data were obtained from 7 studies: 6 data sets were provided by the investigators, one of which was published. The data included fat mass and fat-free mass measured with a QDR 4500A and criteria measurements of body composition from total body water by dilution at 4 centers, densitometry from 1 center, and four-compartment analysis at 2 centers. RESULTS: In the cohort of 1195 subjects, 602 men and 593 women aged 19-82 y with a body mass index (in kg/m2) of 16-44, the fan-beam DXA overestimated fat-free mass (P < 0.05). A significant difference was observed in all 7 data sets, and the mean (+/-SE) was 5 +/- 1%. CONCLUSIONS: It is recommended that the lean soft tissue mass estimate with the fan-beam QDR 4500A be reduced by 5% and that for fat mass be increased by that same mass. This finding is particularly important because the National Health and Nutrition Examination Survey is using the QDR 4500A to assess body composition in a nationally representative sample of persons in the United States.