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Biomedical subjects

K M Flegal

Publications and source records attributed to K M Flegal.

At least 19 recordsLinked to original sources
PubMed2006

Impact of increased overweight on the projected prevalence of osteoporosis in older women.

INTRODUCTION: Overweight is increasing worldwide, but particularly in the United States of America. Higher body weight is associated with higher bone density, so our goal was to estimate whether the higher prevalence of overweight is likely to reduce osteoporosis among older women. METHODS: We calculated the prevalence of osteoporosis by weight status in older women using data from the third National Health and Nutrition Examination Survey (NHANES III, 1988-94). We defined overweight as a body mass index (BMI) >or=25 and osteoporosis as a femur neck bone mineral density (BMD) value 2.5 standard deviations or more below the mean of that of young women. To estimate the expected prevalence of osteoporosis, we applied the prevalence of osteoporosis by weight status from NHANES III to the corresponding weight status prevalence from NHANES 1999-2002. RESULTS: Of older women in NHANES 1999-2002, 68% were overweight compared to 62% in NHANES III. Overweight status was significantly related to osteoporosis prevalence (P < 0.001). However, the expected prevalence of osteoporosis in NHANES 1999-2002 was only slightly lower than that seen in NHANES III (16.8% vs 18.1%, respectively). CONCLUSIONS: The increasing prevalence of overweight among older US women appears unlikely to be accompanied by a significant reduction in osteoporosis.

Aged↗
PubMed2006

Body mass index of healthy men compared with healthy women in the United States.

OBJECTIVE: To compare the distributions of body mass index (BMI) in relatively healthy nonsmoking men and women in the United States. DESIGN: Cross-sectional national survey data from the Third National Health and Nutrition Examination Survey (NHANES III). SUBJECTS: I n total, 11,404 nonsmoking men (n = 4894) and women (n = 6510), ages 20 years and above, drawn from a representative population sample. MEASUREMENTS: Increasingly stringent definitions of 'health' were applied, based on self-reported health, medical history, measurements of blood pressure, blood lipids, serum glucose, glycosylated hemoglobin, and behavioral factors including smoking and physical activity. Main outcome measures were mean and median BMI by health level, 5th and 95th percentiles of BMI, and the prevalence of overweight and obesity. RESULTS: For both men and women, the distribution of BMI became less skewed at better health levels. The range of BMI values that included 90% of healthy men and women was approximately 19.5-30 kg/m2 for men and 18-30 kg/m2 for women, with median values of approximately 24.5 kg/m2 for men and 21.5 kg/m2 for women. The prevalence of overweight declined sharply with increasing health level for women but varied little for men; the prevalence of obesity declined at higher health levels for both men and women. CONCLUSIONS: Only about 5% of healthy younger men or women would be classified as obese by BMI levels. However, the distribution of BMI differs between healthy men and healthy women. Relative to the distribution of BMI values for healthy men, the distribution of BMI values for healthy women is shifted to the left and is more skewed.

Adult↗
PubMed2005

The relative contributions of lean tissue mass and fat mass to bone density in young women.

Although obesity is associated with increased risk of many chronic diseases including cardiovascular disease, diabetes, hypertension, and cancer, there is little evidence to suggest that obesity increases risk of osteoporosis. In fact, both weight and body mass index (BMI) are positive predictors of bone mass in adults, suggesting that those who are overweight or obese may be at lower risk of osteoporosis. However, recent evidence suggests that in children and adolescents, obesity may be associated with lower rather than higher bone mass. To understand the relation of fat mass to bone mass, we examined data gathered from an ethnically diverse group of 921 young women, aged 20-25 years (317 African Americans, 154 Asians, 322 Caucasians, and 128 Latinas) to determine how fat mass (FM) as well as lean tissue mass (LTM) is associated with bone mass. Bone mass, FM, and LTM were measured using dual energy X-ray absorptiometry (GE Lunar Corp, Madison, WI). Bone mass was expressed as bone mineral density (BMD; g/cm2) and bone mineral apparent density (BMAD; g/cm3) for the spine and femoral neck, and as BMD and bone mineral content (BMC; g) for the whole body. Regression techniques were used to examine the following: (1) in separate equations, the associations of LTM and FM with each bone mass parameter; and (2) in the same equation, the independent contributions of LTM and FM to bone mass. LTM and FM were positively correlated with BMD at all skeletal sites. When the contributions of FM and LTM were examined simultaneously, both FM and LTM continued to be positively associated with bone mass parameters but the effect of FM was noted to be smaller than that of LTM. We conclude that in young women, LTM has a greater effect than fat mass on bone density per kg of tissue mass.

Adipose Tissue↗
PubMed2002

Body composition estimates from NHANES III bioelectrical impedance data.

BACKGROUND: Body composition estimates for the US population are important in order to analyze trends in obesity, sarcopenia and other weight-related health conditions. National body composition estimates have not previously been available. OBJECTIVE: To use transformed bioelectrical impedance analysis (BIA) data in sex-specific, multicomponent model-derived prediction formulae, to estimate total body water (TBW), fat-free mass (FFM), total body fat (TBF), and percentage body fat (%BF) using a nationally representative sample of the US population. DESIGN: Anthropometric and BIA data were from the third National Health and Nutrition Examination Survey (NHANES III; 1988-1994). Sex-specific BIA prediction equations developed for this study were applied to the NHANES data, and mean values for TBW, FFM, TBF and %BF were estimated for selected age, sex and racial-ethnic groups. RESULTS: Among the non-Hispanic white, non-Hispanic black, and Mexican-American participants aged 12-80 y examined in NHANES III, 15 912 had data available for weight, stature and BIA resistance measures. Males had higher mean TBW and FFM than did females, regardless of age or racial-ethnic status. Mean TBW and FFM increased from the adolescent years to mid-adulthood and declined in older adult age groups. Females had higher mean TBF and %BF estimates than males at each age group. Mean TBF also increased with older age groups to approximately 60 y of age after which it decreased. CONCLUSIONS: These mean body composition estimates for TBW, FFM, TBF and %BF based upon NHANES III BIA data provide a descriptive reference for non-Hispanic whites, non-Hispanic blacks and Mexican Americans in the US population.

Adolescent↗
PubMed2001

Prevalence of overweight in US children: comparison of US growth charts from the Centers for Disease Control and Prevention with other reference values for body mass index.

BACKGROUND: Several different sets of reference body mass index (BMI) values are available to define overweight in children. OBJECTIVE: The objective of this study was to compare the prevalence of overweight in US children calculated with 3 sets of reference BMI values: the revised growth charts of the Centers for Disease Control and Prevention (CDC-US growth charts), international standards proposed by Cole et al, and values developed by Must et al. DESIGN: Data for children and adolescents came from cross-sectional nationally representative US surveys: cycles II and III of the National Health Examination Survey (1963-1965 and 1966-1970) and the first, second, and third National Health and Nutrition Examination Surveys: NHANES I (1971-1974), II (1976-1980), and III (1988-1994). The reference values of Cole et al equivalent to a BMI of 25 were compared with the 85th percentiles from the other 2 methods; the values equivalent to a BMI of 30 were compared with the 95th percentiles. RESULTS: The 3 methods gave similar but not identical results. The reference values of Cole et al gave lower estimates than did the CDC-US growth charts for young children but higher estimates for older children. The reference values of Must et al gave much higher prevalences for younger girls than did the other 2 methods. CONCLUSIONS: Differences between methods were related to differences in data sets, smoothing methods, and theoretical approaches. All 3 methods are based on statistical criteria and incorporate arbitrary assumptions. These methods should be used cautiously, with awareness of the possible limitations.

Adolescent↗
PubMed2001

Aim for a healthy weight: what is the target?

The first guideline statement of the Year 2000 edition of Nutrition and Your Health: Dietary Guidelines for Americans is "Aim for a healthy weight." The purpose of this paper is to describe the evolution of the weight guideline and discuss some issues related to it. We reviewed current and previous editions of the Dietary Guidelines and the corresponding advisory committee reports. The weight guideline has evolved over the years into one that is complex and touches on a wide range of issues. The 2000 edition emphasizes weight loss more than previous editions. Unlike the other guidelines in the Dietary Guidelines, the weight guideline has a health outcome, a "healthy" weight, rather than a behavioral outcome as its goal. Also unlike the other guidelines, the weight guideline has become more medically oriented over time. The concept of healthy weight in the guidelines includes aspects of body composition, fat distribution and weight-related health conditions. It may be difficult for the public and even for health care providers to interpret some of the concepts included in the weight guideline. Issues related to the appropriate management of weight can be complex and may require a health care provider as a resource for interpretation. Rather than try to incorporate further clinical decision-making and weight loss guidance within the weight guideline, it may be more appropriate to refer the reader to a health care provider for guidance, as was done in previous editions.

Age Factors↗
PubMed2001

Diabetes, impaired fasting glucose, and elevated HbA1c in U.S. adolescents: the Third National Health and Nutrition Examination Survey.

OBJECTIVE: Using population-based data, we estimated the prevalence of diabetes, impaired fasting glucose, and elevated HbA1c (>6%) levels in U.S. adolescents. RESEARCH DESIGN AND METHODS: The Third National Health and Nutrition Examination Survey (1988-1994) examined a representative sample of the U.S. population, which included 2,867 adolescents aged 12-19 years who had serum glucose measured. RESULTS: A total of 13 adolescents in the sample were considered to have diabetes; 9 reported using insulin, 2 reported using oral agents only, and 2 did not report any treatment but had high glucose levels (> or = 11.1 mmol/l regardless of length of fast or > or = 7.0 mmol/l after an 8-h fast). Four of these cases (31% of the sample with diabetes) were considered to have type 2 diabetes. The estimated prevalence of diabetes (all types) per 100 adolescents ages 12-19 years was 0.41% (95% confidence interval 0-0.86). The prevalence of impaired fasting glucose (> or = 6.1 mmol/l) among adolescents without diabetes who had fasted for at least 8 h was 1.76% (0.02-3.50). The prevalence of elevated HbA1c (>6%) was 0.39% (0.04-0.74). CONCLUSIONS: National data reflect the presence of type 2 diabetes in U.S. adolescents, but the survey sample size was not large enough to obtain precise prevalence estimates because of the relatively low prevalence.

Adolescent↗
PubMed2000

CDC growth charts: United States.

OBJECTIVES: This report presents the revised growth charts for the United States. It summarizes the history of the 1977 National Center for Health Statistics (NCHS) growth charts, reasons for the revision, data sources and statistical procedures used, and major features of the revised charts. METHODS: Data from five national health examination surveys collected from 1963 to 1994 and five supplementary data sources were combined to establish an analytic growth chart data set. A variety of statistical procedures were used to produce smoothed percentile curves for infants (from birth to 36 months) and older children (from 2 to 20 years), using a two-stage approach. Initial curve smoothing for selected major percentiles was accomplished with various parametric and nonparametric procedures. In the second stage, a normalization procedure was used to generate z-scores that closely match the smoothed percentile curves. RESULTS: The 14 NCHS growth charts were revised and new body mass index-for-age (BMI-for-age) charts were created for boys and girls (http://www.cdc.gov/growthcharts). The growth percentile curves for infants and children are based primarily on national survey data. Use of national data ensures a smooth transition from the charts for infants to those for older children. These data better represent the racial/ethnic diversity and the size and growth patterns of combined breast- and formula-fed infants in the United States. New features include addition of the 3rd and 97th percentiles for all charts and extension of all charts for children and adolescents to age 20 years. CONCLUSION: Created with improved data and statistical curve smoothing procedures, the United States growth charts represent an enhanced instrument to evaluate the size and growth of infants and children.

Adolescent↗
PubMed2000

Establishing a standard definition for child overweight and obesity worldwide: international survey.

OBJECTIVE: To develop an internationally acceptable definition of child overweight and obesity, specifying the measurement, the reference population, and the age and sex specific cut off points. DESIGN: International survey of six large nationally representative cross sectional growth studies. SETTING: Brazil, Great Britain, Hong Kong, the Netherlands, Singapore, and the United States. SUBJECTS: 97 876 males and 94 851 females from birth to 25 years of age. MAIN OUTCOME MEASURE: Body mass index (weight/height(2)). RESULTS: For each of the surveys, centile curves were drawn that at age 18 years passed through the widely used cut off points of 25 and 30 kg/m(2) for adult overweight and obesity. The resulting curves were averaged to provide age and sex specific cut off points from 2-18 years. CONCLUSIONS: The proposed cut off points, which are less arbitrary and more internationally based than current alternatives, should help to provide internationally comparable prevalence rates of overweight and obesity in children.

Adolescent↗
PubMed2000

Prevalence of pre-obesity and obesity in urban adult Mexicans in comparison with other large surveys.

OBJECTIVE: 1. To estimate the prevalence of pre-obesity and obesity in a 1992 to 1993 national survey of the Mexican urban adult population. 2. To compare our findings with other national surveys and with data for Mexican Americans. RESEARCH METHODS AND PROCEDURES: The national representative sample of the Mexican urban adult population included 8462 women and 5929 men aged 20 to 69 years from 417 towns of >2500 people. Body mass index (BMI), calculated from measured weight and height, was classified using the World Health Organization categories of underweight (BMI < 18.5 kg/m2), normal weight (BMI 18.5 to 24.9 kg/m2), pre-obesity (PreOB = BMI 25 to 29.9 kg/m2) and obesity (OB = BMI 30+ kg/m2). Estimates for Mexican Americans were calculated from U.S. survey data. RESULTS: Overall, 38% of the Mexican urban adult population were classified as pre-obese and 21% as obese. Men had a higher prevalence of pre-obesity than women did at all ages, but women had higher values of obesity. Both pre-obesity and obesity increased with age up to the age range brackets of 40 to 49 or 50 to 59 years for both men and women. Both pre-obesity and obesity prevalence estimates were remarkably similar to data for Mexican Americans from 1982 through 1984. Comparison with other large surveys showed that countries differed more in the prevalence of obesity than of pre-obesity, leading to differences in the PreOB/OB ratio, and that countries also differed in the gender ratio (female/male) for both pre-obesity and obesity. DISCUSSION: Pre-obesity and obesity were high in our population and increased with age. Our approach of characterizing large surveys by PreOB/OB and gender ratios appeared promising.

Adult↗
PubMed2000

Changes in the distribution of body mass index of adults and children in the US population.

BACKGROUND: National survey data show increases in mean body mass index (BMI) and in the prevalence of overweight and obesity for adults and children in the United States, indicating a change in the distribution of BMI. OBJECTIVE: To apply graphical methods to describe changes in the distribution of BMI. DESIGN: BMI values from the third National Health and Nutrition Examination Survey (NHANES III: 1988-94) were compared with data from earlier cross-sectional nationally representative surveys for adults 20-74 y of age and for children and adolescents 6-17 y of age. Tukey mean-difference plots were used to investigate the changes in the distributions of BMI within sex-age groups. RESULTS: Mean-difference plots allow qualitative visual comparisons of the distributions of BMI between surveys. For all sex-age groups, there was increasing skewness with a greater shift in the upper part of the distribution so that, within each group, the heaviest subgroup was heavier in NHANES III than in prior surveys. For the youngest children, the lower part of the distribution showed virtually no change. With increasing age the whole distribution tended to shift upward slightly, suggesting an increase in BMI across the entire population. CONCLUSIONS: These changes in the distribution of BMI suggest the combination of both profound environmental determinants and a population with a high degree of susceptibility. The reasons for the increasing prevalence of obesity should be sought in part by seeking to understand the factors causing increases in the population as a whole.

Adolescent↗
PubMed2000

The effects of age categorization on estimates of overweight prevalence for children.

OBJECTIVE: The objective of this study is to investigate the effects of methods of age grouping on estimates of overweight prevalence for children and adolescents based on reference body mass index (BMI) percentiles. METHODS: Data for children aged 6-17 y came from three nationally representative US surveys, the Third National Health and Nutrition Examination Survey (1988-1994) and Cycles II and III of the National Health Examination Survey (1963-1965, 1966-1970). Month-specific BMI percentile values were taken from the revised US growth charts. Ages were grouped into categories 3, 6 or 12 months in length. Cut-off points were selected as the low or the mean percentile value within the category. Overweight prevalences for these groupings were compared with prevalences calculated using the month-specific values. RESULTS: The effects of grouping and cut-off point selection on overweight prevalence estimates were generally small; however, the combination of 12 month groupings and the low value led to an overestimation by up to 3 percentage points. Within the 12 month groupings, the first 6 months differed systematically from the second 6 months. CONCLUSIONS: Although age categorization may often have little effect on prevalence estimates, prevalence may sometimes be overestimated by as much as 3 percentage points. Use of narrower age categorizations than those used to construct the reference values may result in systematic biases. It is important to understand how age was handled in the construction of the reference population and to select age categories consistent with those used for the reference population.

Adolescent↗
PubMed2000

Criteria for definition of overweight in transition: background and recommendations for the United States.

Overweight and obesity are leading nutrition-related disorders of clinical and public health concern. Assessment and classification of these conditions are dependent on specific body mass index (BMI; in kg/m(2)) cutoff points. US government agencies are making the transition to a revised BMI definition of overweight from that previously recommended for general use. The purpose of this article is to inform the broader medical and scientific communities of the transition that is underway in the United States to identify and classify overweight among adults by using BMI. Historical background on the use of BMI in a variety of applications, as reported in US federal government agency documents, provides an understanding of previous and current weight-for-height guidelines and the basis for arriving at them. On the basis of the current Dietary Guidelines for Americans, US government agencies are moving toward the use of criteria for overweight and obesity that are consistent with current international standards. Clinicians, researchers, and journal editors should be aware of the transition toward a common definition of healthy weight, overweight, and obesity. To facilitate comparisons and reporting of data, others are encouraged to consider making this transition as well.

Adult↗
PubMed2000

Use of GHb (HbA1c) in screening for undiagnosed diabetes in the U.S. population.

OBJECTIVE: To evaluate the use of GHb as a screening test for undiagnosed diabetes (fasting plasma glucose > or =7.0 mmol/l) in a representative sample of the U.S. population. RESEARCH DESIGN AND METHODS: The Third National Health and Nutrition Examination Survey included national samples of non-Hispanic whites, non-Hispanic blacks, and Mexican Americans aged > or =20 years. Of these subjects, 7,832 participated in a morning examination session, of which 1,273 were excluded because of a previous diagnosis of diabetes, missing data, or fasting time of <8 h before examination. Venous blood was obtained to measure fasting plasma glucose and GHb in the remaining 6,559 subjects. Receiver operating characteristic curve analysis was used to examine the sensitivity and specificity of GHb for detecting diabetes at increasing GHb cutoff levels. RESULTS: GHb demonstrated high sensitivity (83.4%) and specificity (84.4%) for detecting undiagnosed diabetes at a GHb cutoff of 1 SD above the normal mean. Moderate sensitivity (63.2%) and very high specificity (97.4%) were evident at a GHb cutoff of 2 SD above the normal mean. Sensitivity at this level ranged from 58.6% in the non-Hispanic white population to 83.6% in the Mexican-American population; specificity ranged from 93.0% in the nonHispanic black population to 98.3% in the non-Hispanic white population. CONCLUSIONS: GHb is a highly specific and convenient alternative to fasting plasma glucose for diabetes screening. A GHb value of 2 SD above the normal mean could identify a high proportion of individuals with undiagnosed diabetes who are at risk for developing diabetes complications.

Adult↗
PubMed1999

Overweight prevalence among youth in the United States: why so many different numbers?

Several recent publications have presented different estimates for the prevalence of overweight among youth in the United States. Prevalence estimates range from 11-24%, despite describing the same results from the third National Health and Nutrition Examination Survey (NHANES III). This paper discusses the variety and evolution of different overweight prevalence estimates. Issues of definition, measurements, criteria selection and comparison groups are considered and implications for estimates of the prevalence of overweight among youth are explored. Reference percentiles for body mass index (BMI) from several publications are compared. The differences in published estimates from NHANES III are noted and explained.

Adolescent↗
PubMed1999

Evaluating epidemiologic evidence of the effects of food and nutrient exposures.

The objective of this paper is to discuss some of the issues to be considered when evaluating and interpreting epidemiologic evidence from observational studies that collect data on dietary intake. The assessment of such evidence should include consideration of the study design, sample selection, and the measurements of exposure and disease. The degree and type of error in nutrient data can lead to analytic problems and potentially be a source of bias either toward or away from the null value. Because methods of statistical correction and adjustment for error, such as energy adjustment, cannot necessarily completely compensate for sources of bias in dietary data, additional research should be conducted on sources of error in dietary data. Published research using reported dietary data should include a discussion of potential sources of error and their effect on the results. The most useful studies are likely to be those designed to address a clearly defined prior hypothesis about a specific diet-disease relation. Because of the potential for bias and confounding, observational epidemiologic studies of diet and outcome cannot generally provide decisive evidence by themselves either for or against specific hypotheses. Although randomized clinical trials of the effects of specific nutrients or dietary modifications are not always feasible, they provide more definitive results and should generally be considered more valid than observational studies using self-reported dietary intake. Well-designed observational epidemiologic studies using self-reported dietary intake can provide valuable data to support or challenge hypotheses derived from clinical or laboratory data and to suggest further directions for investigation.

Bias↗