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Biomedical subjects

Katherine M Flegal

Publications and source records attributed to Katherine M Flegal.

At least 19 recordsLinked to original sources
PubMed2007

Estimation of attributable number of deaths and standard errors from simple and complex sampled cohorts.

Estimates of the attributable number of deaths (AD) from all causes can be obtained by first estimating population attributable risk (AR) adjusted for confounding covariates, and then multiplying the AR by the number of deaths determined from vital mortality statistics that occurred in the population for a specific time period. Proportional hazard regression estimates of adjusted relative hazards obtained from mortality follow-up data from a cohort is combined with a joint distribution of risk factor and confounders to compute an adjusted AR. Two estimators of adjusted AR are examined. These estimators differ according to which reference population is used to obtain the joint distribution of risk factor and confounders. Two types of reference populations were considered: (i) the population represented by the baseline cohort and (ii) a population that is external to the cohort. Methods used in survey sampling are applied to obtain estimates of the variance of the AD estimator. These variances can be applied to data that range from simple random samples to multistage stratified cluster samples, which are used in national household surveys. The variance estimation of AD is illustrated in an analysis of excess deaths due to having a non-ideal body mass index using the second National Health and Examination Survey (NHANES) Mortality Study and the 1999-2002 NHANES. These methods can also be used to estimate the attributable number of cause-specific deaths and their standard errors when the time period for the accrual of deaths is short.

Cohort Studies↗
PubMed2006

Overweight in children: definitions and interpretation.

Studies in a variety of countries have shown increases in the prevalence of overweight among children in recent years. These increases have given rise to concern about children's health and well-being. The terminology used in these studies varies considerably. However, whatever the terminology used, such studies are generally based on weight [expressed as body mass index (BMI), a measure of weight for height, calculated as weight in kilograms divided by the square of height in meters] and not on body fatness per se. There are many different BMI references that can be used to define childhood overweight or obesity. Children are defined as overweight for population surveillance purposes using a variety of BMI cut points. BMI is a screening tool, not a diagnostic tool. Children with a BMI over these cut points do not necessarily have clinical complications or health risks related to overfatness. More in-depth assessment of individual children is required to ascertain health status. The definitions of overweight generally used are working definitions that are valuable for general public health surveillance, screening and similar purposes.

Adolescent↗
PubMed2006

Prevalence of overweight and obesity in the United States, 1999-2004.

CONTEXT: The prevalence of overweight in children and adolescents and obesity in adults in the United States has increased over several decades. OBJECTIVE: To provide current estimates of the prevalence and trends of overweight in children and adolescents and obesity in adults. DESIGN, SETTING, AND PARTICIPANTS: Analysis of height and weight measurements from 3958 children and adolescents aged 2 to 19 years and 4431 adults aged 20 years or older obtained in 2003-2004 as part of the National Health and Nutrition Examination Survey (NHANES), a nationally representative sample of the US population. Data from the NHANES obtained in 1999-2000 and in 2001-2002 were compared with data from 2003-2004. MAIN OUTCOME MEASURES: Estimates of the prevalence of overweight in children and adolescents and obesity in adults. Overweight among children and adolescents was defined as at or above the 95th percentile of the sex-specific body mass index (BMI) for age growth charts. Obesity among adults was defined as a BMI of 30 or higher; extreme obesity was defined as a BMI of 40 or higher. RESULTS: In 2003-2004, 17.1% of US children and adolescents were overweight and 32.2% of adults were obese. Tests for trend were significant for male and female children and adolescents, indicating an increase in the prevalence of overweight in female children and adolescents from 13.8% in 1999-2000 to 16.0% in 2003-2004 and an increase in the prevalence of overweight in male children and adolescents from 14.0% to 18.2%. Among men, the prevalence of obesity increased significantly between 1999-2000 (27.5%) and 2003-2004 (31.1%). Among women, no significant increase in obesity was observed between 1999-2000 (33.4%) and 2003-2004 (33.2%). The prevalence of extreme obesity (body mass index > or =40) in 2003-2004 was 2.8% in men and 6.9% in women. In 2003-2004, significant differences in obesity prevalence remained by race/ethnicity and by age. Approximately 30% of non-Hispanic white adults were obese as were 45.0% of non-Hispanic black adults and 36.8% of Mexican Americans. Among adults aged 20 to 39 years, 28.5% were obese while 36.8% of adults aged 40 to 59 years and 31.0% of those aged 60 years or older were obese in 2003-2004. CONCLUSIONS: The prevalence of overweight among children and adolescents and obesity among men increased significantly during the 6-year period from 1999 to 2004; among women, no overall increases in the prevalence of obesity were observed. These estimates were based on a 6-year period and suggest that the increases in body weight are continuing in men and in children and adolescents while they may be leveling off in women.

Adolescent↗
PubMed2006

Blood lead levels and death from all causes, cardiovascular disease, and cancer: results from the NHANES III mortality study.

BACKGROUND: Analyses of mortality data for participants examined in 1976-1980 in the second National Health and Nutrition Examination Survey (NHANES II) suggested an increased risk of mortality at blood lead levels > 20 microg/dL. Blood lead levels have decreased markedly since the late 1970s. In NHANES III, conducted during 1988-1994, few adults had levels > 20 microg/dL. OBJECTIVE: Our objective in this study was to determine the risk of mortality in relation to lower blood lead levels observed for adult participants of NHANES III. METHODS: We analyzed mortality information for 9,757 participants who had a blood lead measurement and who were > or = 40 years of age at the baseline examination. Using blood lead levels categorized as < 5, 5 to < 10, and > or = 10 microg/dL, we determined the relative risk of mortality from all causes, cancer, and cardiovascular disease through Cox proportional hazard regression analysis. RESULTS: Using blood lead levels < 5 microg/dL as the referent, we determined that the relative risk of mortality from all causes was 1.24 [95% confidence interval (CI), 1.05-1.48] for those with blood levels of 5-9 microg/dL and 1.59 (95% CI, 1.28-1.98) for those with blood levels > or = 10 microg/dL (p for trend < 0.001). The magnitude of risk was similar for deaths due to cardiovascular disease and cancer, and tests for trend were statistically significant (p < 0.01) for both causes of death. CONCLUSION: In a nationally representative sample of the U.S. population, blood lead levels as low as 5-9 mug/dL were associated with an increased risk of death from all causes, cardiovascular disease, and cancer.

Cardiovascular Diseases↗
PubMed2006

Prevalence of diabetes and impaired fasting glucose in adults in the U.S. population: National Health And Nutrition Examination Survey 1999-2002.

OBJECTIVE: The purpose of this study was to examine the prevalences of diagnosed and undiagnosed diabetes, and impaired fasting glucose (IFG) in U.S. adults during 1999-2002, and compare prevalences to those in 1988-1994. RESEARCH DESIGN AND METHODS: The National Health and Nutrition Examination Survey (NHANES) contains a probability sample of adults aged > or =20 years. In the NHANES 1999-2002, 4,761 adults were classified on glycemic status using standard criteria, based on an interview for diagnosed diabetes and fasting plasma glucose measured in a subsample. RESULTS: The crude prevalence of total diabetes in 1999-2002 was 9.3% (19.3 million, 2002 U.S. population), consisting of 6.5% diagnosed and 2.8% undiagnosed. An additional 26.0% had IFG, totaling 35.3% (73.3 million) with either diabetes or IFG. The prevalence of total diabetes rose with age, reaching 21.6% for those aged > or =65 years. The prevalence of diagnosed diabetes was twice as high in non-Hispanic blacks and Mexican Americans compared with non-Hispanic whites (both P < 0.00001), whereas the prevalence of undiagnosed diabetes was similar by race/ethnicity, adjusted for age and sex. The prevalence of diagnosed diabetes was similar by sex, but prevalences of undiagnosed diabetes and IFG were significantly higher in men. The crude prevalence of diagnosed diabetes rose significantly from 5.1% in 1988-1994 to 6.5% in 1999-2002, but the crude prevalences were stable for undiagnosed diabetes (from 2.7 to 2.8%) and IFG (from 24.7 to 26.0%). Results were similar after adjustment for age and sex. CONCLUSIONS: Although the prevalence of diagnosed diabetes has increased significantly over the last decade, the prevalences of undiagnosed diabetes and IFG have remained relatively stable. Minority groups remain disproportionately affected.

Adult↗
PubMed2005

Epidemiologic aspects of overweight and obesity in the United States.

National survey data from the U.S. show that the prevalence of overweight and obesity among adults remained relatively constant over the 20-year period from 1960 to 1980, began to increase around the mid-1980s and has continued to increase. Data for children and adolescents, based on different definitions, show the same pattern. It can sometimes be more useful to look at the whole distribution of body mass index, rather than on prevalence estimates based on pre-defined cutoffs. Data from several countries suggest that for both adults and children, the distribution of BMI has become more skewed over time. Although many hypotheses have been put forward about the causes of the increases, data to address these issues are sparse. Obesity is a well-known risk factor for numerous health conditions. Nonetheless, the health consequences of the increases in obesity have not been fully delineated. Increases in diabetes have been noted in conjunction with the rise in obesity. On the other hand, declines in some other cardiovascular risk factors have been seen at all BMI levels. Rising life expectancy and decreasing heart disease mortality rates seem to confound some of the expectations about the effects of increasing obesity on mortality. The effects of obesity on morbidity may be greater than its effects on mortality. The increasing prevalence of obesity poses challenges for researchers and for policy makers.

Adolescent↗
PubMed2005

Excess deaths associated with underweight, overweight, and obesity.

CONTEXT: As the prevalence of obesity increases in the United States, concern over the association of body weight with excess mortality has also increased. OBJECTIVE: To estimate deaths associated with underweight (body mass index [BMI] <18.5), overweight (BMI 25 to <30), and obesity (BMI > or =30) in the United States in 2000. DESIGN, SETTING, AND PARTICIPANTS: We estimated relative risks of mortality associated with different levels of BMI (calculated as weight in kilograms divided by the square of height in meters) from the nationally representative National Health and Nutrition Examination Survey (NHANES) I (1971-1975) and NHANES II (1976-1980), with follow-up through 1992, and from NHANES III (1988-1994), with follow-up through 2000. These relative risks were applied to the distribution of BMI and other covariates from NHANES 1999-2002 to estimate attributable fractions and number of excess deaths, adjusted for confounding factors and for effect modification by age. MAIN OUTCOME MEASURES: Number of excess deaths in 2000 associated with given BMI levels. RESULTS: Relative to the normal weight category (BMI 18.5 to <25), obesity (BMI > or =30) was associated with 111,909 excess deaths (95% confidence interval [CI], 53,754-170,064) and underweight with 33,746 excess deaths (95% CI, 15,726-51,766). Overweight was not associated with excess mortality (-86,094 deaths; 95% CI, -161,223 to -10,966). The relative risks of mortality associated with obesity were lower in NHANES II and NHANES III than in NHANES I. CONCLUSIONS: Underweight and obesity, particularly higher levels of obesity, were associated with increased mortality relative to the normal weight category. The impact of obesity on mortality may have decreased over time, perhaps because of improvements in public health and medical care. These findings are consistent with the increases in life expectancy in the United States and the declining mortality rates from ischemic heart disease.

Adult↗
PubMed2005

Secular trends in cardiovascular disease risk factors according to body mass index in US adults.

CONTEXT: Prevalence of obesity in the United States has increased dramatically in recent decades, but the magnitude of change in cardiovascular disease (CVD) risk factors among the growing proportion of overweight and obese Americans remains unknown. OBJECTIVE: To examine 40-year trends in CVD risk factors by body mass index (BMI) groups among US adults aged 20 to 74 years. DESIGN, SETTING, AND PARTICIPANTS: Analysis of 5 cross-sectional, nationally representative surveys: National Health Examination Survey (1960-1962); National Health and Nutrition Examination Survey (NHANES) I (1971-1975), II (1976-1980), and III (1988-1994); and NHANES 1999-2000. MAIN OUTCOME MEASURES: Prevalence of high cholesterol level (> or =240 mg/dL [> or =6.2 mmol/L] regardless of treatment), high blood pressure (> or =140/90 mm Hg regardless of treatment), current smoking, and total diabetes (diagnosed and undiagnosed combined) according to BMI group (lean, <25; overweight, 25-29; and obese, > or =30). RESULTS: The prevalence of all risk factors except diabetes decreased over time across all BMI groups, with the greatest reductions observed among overweight and obese groups. Compared with obese persons in 1960-1962, obese persons in 1999-2000 had a 21-percentage-point lower prevalence of high cholesterol level (39% in 1960-1962 vs 18% in 1999-2000), an 18-percentage-point lower prevalence of high blood pressure (from 42% to 24%), and a 12-percentage-point lower smoking prevalence (from 32% to 20%). Survey x BMI group interaction terms indicated that compared with the first survey, the prevalence of high cholesterol in the fifth survey had fallen more in obese and overweight persons than in lean persons (P<.05). Survey x BMI changes in blood pressure and smoking were not statistically significant. Changes in risk factors were accompanied by increases in lipid-lowering and antihypertensive medication use, particularly among obese persons. Total diabetes prevalence was stable within BMI groups over time, as nonsignificant 1- to 2-percentage-point increases occurred between 1976-1980 and 1999-2000. CONCLUSIONS: Except for diabetes, CVD risk factors have declined considerably over the past 40 years in all BMI groups. Although obese persons still have higher risk factor levels than lean persons, the levels of these risk factors are much lower than in previous decades.

Adult↗
PubMed2004

Mean body weight, height, and body mass index, United States 1960-2002.

This report presents trends in national estimates of mean weight, height, and body mass index (BMI) from the National Health Examination and the National Health and Nutrition Examination Surveys between 1960 and 2002. The tables included in this report present data for adults by sex, race/ethnicity, and age group and for children by sex and year of age. Mean weight and BMI have increased for both sexes, all race/ethnic groups, and all ages. Among adults, mean weight increased more than 24 pounds. Although not as dramatically, mean height has also increased for most ages and for both males and females.

Adolescent↗
PubMed2004

Methods of calculating deaths attributable to obesity.

Previously reported estimates of deaths attributable to obesity in the United States have been based on a method that only partially adjusts for confounding and does not allow for effect modification. In this study, the authors investigated the possible magnitude and direction of bias in estimating deaths attributable to obesity when such a method is used. Hypothetical examples are based on 1991 US population data and published relative risks. Incomplete adjustment for confounding of the obesity-mortality relation by age and sex led to a 17% overestimation of deaths due to obesity. Additional bias resulted from slight differences between the derivation cohort and the target population. For example, a difference of three percentage points in the proportion of people 80 years of age or older led to a 42% overestimation of deaths due to obesity. In addition, these estimates appear to be sensitive to minor differences in relative risks between a derivation cohort and the target population. A difference of 0.20 in relative risks almost doubled the number of deaths (97% overestimation). Estimates of deaths attributable to obesity can be biased if confounding and effect modification are not properly taken into account or if the relative risks are not estimated accurately.

Adolescent↗
PubMed2004

Prevalence of overweight and obesity among US children, adolescents, and adults, 1999-2002.

CONTEXT: The prevalence of overweight and obesity has increased markedly in the last 2 decades in the United States. OBJECTIVE: To update the US prevalence estimates of overweight in children and obesity in adults, using the most recent national data of height and weight measurements. DESIGN, SETTING, AND PARTICIPANTS: As part of the National Health and Nutrition Examination Survey (NHANES), a complex multistage probability sample of the US noninstitutionalized civilian population, both height and weight measurements were obtained from 4115 adults and 4018 children in 1999-2000 and from 4390 adults and 4258 children in 2001-2002. MAIN OUTCOME MEASURE: Prevalence of overweight (body mass index [BMI] > or =95th percentile of the sex-specific BMI-for-age growth chart) among children and prevalence of overweight (BMI, 25.0-29.9), obesity (BMI > or =30.0), and extreme obesity (BMI > or =40.0) among adults by sex, age, and racial/ethnic group. RESULTS: Between 1999-2000 and 2001-2002, there were no significant changes among adults in the prevalence of overweight or obesity (64.5% vs 65.7%), obesity (30.5% vs 30.6%), or extreme obesity (4.7% vs 5.1%), or among children aged 6 through 19 years in the prevalence of at risk for overweight or overweight (29.9% vs 31.5%) or overweight (15.0% vs 16.5%). Overall, among adults aged at least 20 years in 1999-2002, 65.1% were overweight or obese, 30.4% were obese, and 4.9% were extremely obese. Among children aged 6 through 19 years in 1999-2002, 31.0% were at risk for overweight or overweight and 16.0% were overweight. The NHANES results indicate continuing disparities by sex and between racial/ethnic groups in the prevalence of overweight and obesity. CONCLUSIONS: There is no indication that the prevalence of obesity among adults and overweight among children is decreasing. The high levels of overweight among children and obesity among adults remain a major public health concern.

Adolescent↗
PubMed2004

Body mass index and obesity-related metabolic disorders in Taiwanese and US whites and blacks: implications for definitions of overweight and obesity for Asians.

BACKGROUND: Recommendations based on scanty data have been made to lower the body mass index (BMI; in kg/m(2)) cutoff for obesity in Asians. OBJECTIVE: The goal was to compare relations between BMI and metabolic comorbidity among Asians and US whites and blacks. METHODS: We compared the prevalence rate, sensitivity, specificity, predictive values, and impact fraction of comorbidities at each BMI level and the BMI-comorbidity relations across ethnic groups by using data from the third National Health and Nutrition Examination Survey and the Nutrition and Health Survey in Taiwan (1993-1996). RESULTS: For most BMI values, the prevalences of hypertension, diabetes, and hyperuricemia were higher for Taiwanese than for US whites. In addition, increments of BMI corresponded to higher odds ratios in Taiwanese than in US whites for hypertriglyceridemia (P = 0.01) and hypertension (P = 0.075). BMI-comorbidity relations were stronger in Taiwanese than in US blacks for all comorbidities studied. BMIs of 22.5, 26, and 27.5 were the cutoffs with the highest sum of positive and negative predictive value for Taiwanese, US white, and US black men, respectively. The same order was observed for women. For BMIs >27, >85% of Taiwanese, 66% of whites, and 55% of blacks had at least one of the studied comorbidities. However, a cutoff close to the median of the studied population was often found by maximizing sensitivity and specificity. Reducing BMI from >25 to <25 in persons in the United States could eliminate 13% of the obesity comorbidity studied. The corresponding cutoff in Taiwan is slightly <24. CONCLUSION: These data suggest a possible need to set lower BMI cutoffs for Asians, but where to draw the line is a complex issue.

Adult↗
PubMed2004

Prevalence and trends in overweight in Mexican-american adults and children.

Overweight and obesity have been increasing in many countries. Our objective is to describe the trends in overweight and obesity occurring in the Mexican-American population in the United States. Data on measured height and weight for Mexican Americans come from the following surveys: the Hispanic Health and Nutrition Examination Survey (HHANES, 1982-84), the Third National Health and Nutrition Examination Survey (NHANES III, 1988-94), and NHANES 1999-2002. In 1999-2002, 73% of Mexican-American adults were overweight and 33% were obese. Obesity increased between NHANES III and NHANES 1999-2002, from 24% to 27% for men and from 35% to 38% for women. Increases were also seen for children and adolescents. The Mexican-American population in the United States, both children and adults, is showing trends in overweight and obesity over time that are similar to those seen in other segments of the U.S. population and indeed in many countries.

Adolescent↗
PubMed2004

Estimating deaths attributable to obesity in the United States.

Estimates of deaths attributable to obesity in the United States rely on estimates from epidemiological cohorts of the relative risk of mortality associated with obesity. However, these relative risk estimates are not necessarily appropriate for the total US population, in part because of exclusions to control for baseline health status and exclusion or underrepresentation of older adults. Most deaths occur among older adults; estimates of deaths attributable to obesity can vary widely depending on the assumptions about the relative risks of mortality associated with obesity among the elderly. Thus, it may be difficult to estimate deaths attributable to obesity with adequate accuracy and precision. We urge efforts to improve the data and methods for estimating this statistic.

Adult↗