Lori G. Borrud

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.

Fecal Incontinence in US Adults: Epidemiology and Risk Factors

BACKGROUND & AIMS The study aims were to estimate the prevalence of different types and frequencies of fecal incontinence (FI), describe demographic factors, and identify risk factors. METHODS The National Health and Nutrition Examination Survey (NHANES) assesses health status in the civilian noninstitutionalized US population. The validated Fecal Incontinence Severity Index was added to NHANES in 2005-2006. Participants were 2229 women and 2079 men aged 20 years or older. FI was defined as accidental leakage of solid, liquid, or mucus at least once in the preceding month. Sampling weights were used to obtain prevalence estimates for the national population. Multivariate logistic regression identified independent risk factors. RESULTS The estimated prevalence of FI in noninstitutionalized US adults is 8.3% (95% confidence interval, 7.1-9.5) and consists of liquid stool in 6.2%, solid stool in 1.6%, and mucus in 3.1%. It occurs at least weekly in 2.7%. Prevalence is similar in women (8.9%) and men (7.7%) and increases with age from 2.6% in 20 to 29 year olds up to 15.3% in participants aged 70 years and older. FI is not significantly associated with race/ethnicity, education, income, or marital status after adjusting for age. Independent risk factors in women are advancing age, loose or watery stools, more than 21 stools per week, multiple chronic illnesses, and urinary incontinence. Independent risk factors in men are age, loose or watery stools, poor self-rated health, and urinary incontinence. CONCLUSIONS FI is a prevalent age-related disorder. Chronic diarrhea is a strong modifiable risk factor that may form the basis for prevention and treatment.

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. Copyright

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.

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.

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 ≥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.

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.

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.