National Health and Nutrition Examination Survey: where nutrition meets medicine for the benefit of health

¹ From the Harvard Medical School, Beth Israel Deaconess Medical Center, Boston.

See corresponding article on page 228.

² Reprints not available. Address correspondence to GL Blackburn, Beth Israel Deaconess Medical Center, Center for the Study of Nutrition Medicine, Feldberg 8, East Campus, 330 Brookline Avenue, Boston, MA 02215. E-mail: gblackbu{at}bidmc.harvard.edu.

Few in the nutrition field are unaware of the National Health and Nutrition Examination Survey (NHANES) (1), and few in the medical field are unaware of the metabolic syndrome, particularly now that it has an ICD-9 (International Classification of Diseases, 9th revision) code as a medical diagnosis (2). At the Columbia University College of Physicians and Surgeons in New York, the Institute of Human Nutrition and the Obesity Research Center at St Luke’s–Roosevelt Hospital are merging NHANES databases and medical knowledge in ways that allow both organizations to collaborate on key issues surrounding the metabolic syndrome, including the validity of diagnostic criteria across ethnic groups and the development of an evidence-based approach to clinical care (3).

The merger of information from NHANES and information on the metabolic syndrome is no easy task. A MEDLINE (National Institute of Medicine, Bethesda, MD) search produced 7637 citations on NHANES, 454 on NHANES III, and 9680 on the metabolic syndrome (not including its pseudonyms, eg, insulin resistance syndrome, syndrome X, and dysmetabolic syndrome). The annotated bibliography of NHANES-based publications from 1997 to 1999 alone is 165 pages in length (4). Data indicate that some 47 million US residents have the metabolic syndrome (3,5), and growth in the numbers of overweight, obese, and elderly persons will only increase its prevalence and the magnitude of its public health implications (6).

In an earlier study, Park et al (3) reported the prevalence of and associated risk factors for the metabolic syndrome by ethnicity, socioeconomic status, and several lifestyle factors. Increased risk was associated with older age, postmenopausal status, Mexican American ethnicity, higher body mass index (BMI; in kg/m²), current smoking, low household income, high (> 60%) carbohydrate intake, alcohol consumption, and low physical activity.

The Columbia group previously reported that < 6% of normal-weight adults met the study criteria for metabolic syndrome, but that rates for the syndrome increased in the overweight participants and reached a prevalence of 60% in the moderately obese participants (ie, those with a BMI of 35). They derived odds ratio equations for metabolic syndrome from logistic regression models for percentage body fat that were consistent with the risk of metabolic syndrome at traditional BMI cutoffs. Starting with the overweight group, the odds ratios for metabolic syndrome increased as a function of BMI. At a BMI > 30, which indicates obesity, the incidence of the metabolic syndrome in men exceeded that in women. This indicates that men may be more sensitive to excessive weight gain than are women.

Ethnic differences in the relations between BMI, percentage body fat, and the metabolic syndrome have also been found (7). Higher adiposity is associated with higher fasting insulin concentrations in Hispanic men and women (8). Other data show that at the same BMI, percentage body fat differs between Asians, African Americans, and whites after control for sex, age, height, and weight (9,10).

Previously, Gallagher et al (9) associated percentage body fat with BMI thresholds of 18.5, 25, and 30. In this issue of the Journal, Zhu et al (11) report on the risk of metabolic syndrome relative to percentage body fat. Their rationale was that recognized physiologic mechanisms associate total and regional body fat with insulin resistance, glucose metabolism, serum lipid concentrations, and blood pressure. Therefore, the use of percentage body fat thresholds consistent with the risk of metabolic syndrome at traditional BMI cutoffs would provide equations for estimating the odds of the disease at any given percentage body fat, sex, and race.

Although percentage body fat is not necessarily a better marker for the metabolic syndrome than is BMI, this approach relates the biomarker to the pathophysiology of the disease and to disease risk. Many studies have shown that BMI is a reasonable index of adiposity. Furthermore, fat distribution has already been established as an important indicator of the metabolic syndrome (12). Diagnostic criteria of the Adult Treatment Panel III of the National Cholesterol Education Program Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults included waist circumference as a proxy measure of abdominal obesity. Waist circumference is well correlated with visceral adipose tissue and is a better anthropometric predictor of metabolic risk factors than is BMI (13,14).

Detecting overweight persons with metabolic syndrome and implementing preventive lifestyle interventions—diet education, physical activity, weight control, smoking cessation, and related behavior modification—is a clinical priority (14,15). Waist circumference, which is easily measured, is a simple and useful tool for identifying patients who are susceptible to the metabolic syndrome. Other methods under study include bioelectrical impedance analysis and dual-energy X-ray absorptiometry (DXA), an approach that appears to have great promise.

NHANES IV will be key to realizing the promise of DXA and other advances in phenotyping for the metabolic syndrome. As of 2002, data from the US Department of Agriculture’s Continuing Survey of Food Intakes by Individuals are being merged with the NHANES data, resulting in a new database of comprehensive information on health and nutrition characteristics of US residents. Plans to use a food-frequency questionnaire, a wearable physical activity monitor, and DXA measurements of body composition will provide individual estimates of usual intake and body composition as well as population-wide distributions.

Since the 1956 National Health Survey Act authorized a continuing survey to provide current statistical data on the amount, distribution, and effects of illness and disability in the United States, the Columbia group and many other investigators have produced thousands of analyses. With NHANES III, the group was handicapped because they had to wait, sometimes as long as 10 y, for representative data from the entire 6-y sample period. In contrast, NHANES IV is a continuous survey in which data are collected from a representative sample of the US population every year at 15 locations; 5000 people are surveyed annually. The sample population will include 40 000 adults and children.

NHANES data have already influenced public policy and improved the nation’s health in many ways. Enhancements in the design and methods of NHANES IV will allow for increased flexibility in survey content and more precise investigations. Ultimately, NHANES IV will bring nutrition and medicine together to improve health promotion and disease prevention.

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Related articles in AJCN:

Percentage body fat ranges associated with metabolic syndrome risk: results based on the third National Health and Nutrition Examination Survey (1988–1994)

Shankuan Zhu, ZiMian Wang, Wei Shen, Steven B Heymsfield, and Stanley Heshka
AJCN 2003 78: 228-235. [Full Text]