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Trends of Abdominal Adiposity in White, Black, and Mexican-American Adults, 1988 to 2000 Ike S. Okosun,* Simon T. Choi,† John M. Boltri,‡ David C. Parish,§ K.M. Dinesh Chandra,§ G.E. Alan Dever,* and Amy Lucas*

Abstract OKOSUN, IKE S., SIMON T. CHOI, JOHN M. BOLTRI, DAVID C. PARISH, K.M. DINESH CHANDRA, G.E. ALAN DEVER, AND AMY LUCAS. Trends of abdominal adiposity in white, black, and Mexican-American adults, 1988 to 2000. Obes Res. 2003;11:1010 –1017. Objective: To describe changes in the distribution of waist circumference (WC) and abdominal obesity (AO) in white, black, and Mexican-American adults from 1988 through 2000. Research Methods and Procedures: Nationally representative cross-sectional surveys of adults 20 to 79 years of age were examined using data from U.S. National Health and Nutrition Examination Surveys of 1988 to 1994 and 1999 to 2000. AO was defined as WC ⱖ102 cm in men and ⱖ88 cm in women. Results: There was a gradient of increasing WC and AO with increasing age in both study periods in whites and blacks. In men, the average increase between the study periods in overall WC in whites, blacks, and Mexican Americans were 3, 3.3, and 3.4 cm, respectively. The corresponding values in women were 2.4, 5.3, and 3.7 cm, respectively. In men, the percentage change in prevalence of AO between 1988 and 2000 ranged from 5.5% in MexicanAmerican men to 8.2% in white men. In women, there was a 1.7% decrease in AO in Mexican Americans, whereas there was an increase of 6.3% for whites and 7% for blacks.

Received for review March 25, 2003. Accepted in final form June 12, 2003. *Department of Community Medicine, ‡Department of Family Medicine, and §Department of Internal Medicine, Mercer University School of Medicine, Macon, Georgia; and †Department of Preventive Medicine, University of Kansas Medical Center, Kansas City, Kansas. Address correspondence to Ike S. Okosun, Associate Professor of Community Medicine, Department of Community Medicine, Mercer University School of Medicine, 1550 College Street, Macon, GA 31207. E-mail: [email protected] Copyright © 2003 NAASO

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Discussion: Despite increased understanding of the need for screening and treatment for obesity, this study indicates increasing prevalence of AO in white and black Americans. Without concerted effort to reduce the prevalence of overall obesity, the increasing prevalence of AO is likely to lead to increased prevalence of metabolic syndromes in the United States. Our results highlight the need to design evidencebased programs that show promise for long-term health behavior changes to facilitate the prevention of AO and related comorbidities. Key words: abdominal fat, ethnicity, fat patterning

Introduction

Abdominal obesity (AO)1 is an important public health problem and is a component of cardiovascular risks (1,2). AO is associated with the metabolic syndrome, which includes hypertension, hyperinsulinemia, glucose intolerance, hypertriglyceridemia, elevated levels of low-density lipoprotein, and low levels of high-density lipoprotein cholesterol (3– 8). AO is also linked with cancers of many sites, including breast, colon, and the kidney (9 –11). Whereas the best methods for estimating abdominal fat patterning are by imaging techniques such as magnetic resonance and computed tomography, an anthropometric surrogate [waist circumference (WC)] is used for largescale population-based studies. Measurement of WC is simple, requiring only a tape and little training. Also, WC is highly correlated with visceral adiposity, which is recognized as the most metabolically active form of adiposity (12,13). The mechanism linking AO with cardiovascular diseases is poorly understood. However, the link may be due to its

1 Nonstandard abbreviations: AO, abdominal obesity; WC, waist circumference; NIH, National Institutes of Health; NHANES, National Health and Nutrition Examination Survey.

Abdominal Adiposity in Ethnic Groups, Okosun et al.

correlation with visceral obesity. Two possible mechanisms have been suggested for the mode of action of AO in cardiovascular diseases: 1) through the predominance of the highly sensitive lipolytic hypertrophied visceral adipose tissues, free fatty acids may provoke insulin resistance (14,15); and 2) elevated free testosterone and reduced sexhormone-binding globulin may be triggers for increased abdominal adiposity and reduced fractional hepatic extraction of insulin (16). Thus, the association of adiposity with cardiovascular diseases may be caused by visceral fat depot discharging free fatty acids into the portal and systemic circulation (17). National Institute of Health (NIH) Clinical Guidelines recommend the measurement of waist as a screening tool for health risk (18). The NIH guideline advocates risk stratification based on WC. WC values of 102 cm or greater in men and 88 cm or greater in women are the cut-off points for AO (18,19). These WC cut-off points were proposed by Lean et al. (20) and later by Han et al. (21) to assist professionals in managing subjects with obesity-related comorbidities. Sexual dimorphism and ethnic differences are well known for AO (22–24). As suggested by some investigations, blacks have higher upper-body adiposity, based on WC, compared with whites (23,24). Blacks’ susceptibility to AO may be due to their larger visceral fat deposits (23,25). Indeed, some investigators suggest that blacks’ propensity to metabolic aberrations may be a result of excess visceral adiposity compared with whites. Others have postulated that racial differences with regard to upper body fat cells may be associated with racial differences in metabolic risk factors (26). Despite racial/ethnic differences in AO, no data exist describing ethnic trends in AO estimated from WC in U.S. adults. Hence, in this report, we describe the changes in the distribution of WC in white, black, and Mexican-American adult men and women from 1988 through 2000. We also sought to determine the prevalence and trends in AO, using the NIH expert panel and World Health Organization consultation group recommended definitions (18,19).

Research Methods and Procedures Data Source The U.S. National Center for Health Statistics provided datasets that were used in this study. These datasets represent two time periods, 1988 –1994 and 1999 –2000, that were from cross-sectional surveys with similar designs and were carried out among noninstitutionalized U.S. civilian populations. Descriptions of the plan and operation of these surveys have been described by other investigators (27,28). Briefly, these two surveys have a similar structure and design and are national in scope. The U.S. National Health and Nutrition Examination Survey (NHANES) III (1988 –1994) was based on a com-

plex, multi-stage sampling plan. This survey was the first examination survey without an upper age limit. Also, in NHANES III, a home examination option was employed for the first time to obtain examination data for very young children and for elderly persons who were unable to visit the mobile examination centers. Approximately 30,818 persons were examined in NHANES III. NHANES 1999 to 2000 is the most recent of the health examination surveys carried out by the U.S. National Center for Health Statistics. The NHANES 1999 to 2000 was a stratified multistage probability sample based on selection of counties, blocks, households, and persons within households. Like NHANES III, NHANES 1999 to 2000 was designed to oversample Mexican Americans and non-Hispanic blacks to improve estimates for these groups. Approximately 9965 persons completed the NHANES 1999 to 2000 survey. Only adults who were identified as non-Hispanic white, non-Hispanic black, or Mexican American between 20 to 79 years old were included in this investigation. This study was also restricted to subjects who were measured for WCs. Women who were pregnant at the time of the surveys were excluded from this analysis. In the surveys, waist measurements were made at the natural waist midpoint between the lowest aspect of the rib cage and highest point of the iliac crest (to the nearest 0.1 cm). Definition of Terms AO was defined as WC ⱖ102 and ⱖ88 cm for men and women, respectively (18,19). Statistical Analysis Statistical programs available in SAS for Windows (29) and SUDAAN (30) were used for this analysis. To account for unequal probabilities of selection, oversampling, and nonresponse, appropriate sample weights were used for the analyses. SE estimates were calculated using the SUDAAN statistical program. For NHANES III, the Taylor series linearization method was used to estimate SEs (30). For NHANES 1999 to 2000, SEs were estimated by means of the delete 1 jackknife method (31), partitioning the sample into 52 replicates by deleting one unit at a time. WC was normalized using Log10, and overall and agespecific differences in WC among ethnic groups were assessed using one-way ANOVA. Sex-specific distribution of WC in the population was evaluated using nonparametric smoothed curves, based on sequential calculations of running medians for groups with adjacent points (32). Prevalences of AO were age-adjusted by direct methods using the 2000 U.S. population census data and employing 20 to 39, 40 to 59, and ⱖ60 year age groupings. These age categories are consistent with the NHANES 1999 to 2000 sample design age groups that have been recommended for analyses. The customary 95%CIs and p values of ⬍0.05 were used to indicate statistical significance. OBESITY RESEARCH Vol. 11 No. 8 August 2003

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Results A total of 8272 white, 5122 black, and 5346 MexicanAmerican subjects were eligible for this investigation. Overall and age-specific mean values of WC stratified by sex are provided in Table 1. In men, the average increases between the 1988 to 1994 and 1999 to 2000 periods in overall WC in whites, blacks, and Mexican Americans were 3, 3.3, and 3.4 cm, respectively. The corresponding values in women were 2.4, 5.3, and 3.7 cm, respectively. There was a gradient of increasing WC with increasing age in both study periods in white, black, and Mexican-American men and women. In men, whites had overall and age-specific WC values that were higher than those of blacks and Mexican Americans for both 1988 to 1994 and 1999 to 2000 (p ⬍ 0.05). A significantly higher WC was also observed in 1999 to 2000 compared with the 1988 to 1994 period for men of all three ethnic groups. The largest absolute difference between study periods in WC was observed in the 20to 39-year-old Mexican-American men, with a difference of 8.7 cm. In women, blacks had greatest overall and agespecific WC compared with whites and Mexican Americans in both study periods. In women, the largest difference between study periods in WC was observed in the 20- to 39-year-old black women, with a difference of 4.7 cm. The distribution of WC in the population was evaluated in white, black and Mexican-American men and women for the 1988 to 1994 and 1999 to 2000 study periods (Figure 1). In men, the distribution curves shifted to the right, indicating higher WC in 1999 to 2000 for each of the ethnic groups that were investigated. A similar pattern was observed in women, and the shift to the right tended to be greater in women than men. Also, in women, shifts to higher WC values were greater in blacks than in whites and MexicanAmericans. The prevalence of AO during 1988 to 2000 stratified by age and sex for those subjects who were 20 years old and older and age-specific groups are shown in Table 2. There were statistically significant differences in overall prevalence of AO in the two study periods in both men and women (p ⬍ 0.01). In men, the change in prevalence of AO between 1988 to 1994 and 1999 to 2000 ranged from 5.5% in Mexican-American men to 8.2% in white men. In women, there was a 1.7% decrease in AO in Mexican Americans compared with an increase of 6.3% for whites and 7% for blacks. Compared with black men, black women were 39.4% more abdominally obese in 1988 to 1994 and 38.7% more obese in 1999 to 2000.

Discussion Concern about AO is not new. In 1956, Vague (33) postulated that gynoid and android body habitue´ s might play a role in cardiovascular diseases. This concept has subsequently been popularized by Lean et al. (20) and Han 1012

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et al. (21) and has gained considerable support from different studies. AO is now recognized as an important factor in insulin resistance syndrome. Because of the voluminous data in recent years regarding the negative effects of obesity, we hypothesized a statistically significant decrease in the prevalence of AO in the 1999 to 2000 period compared with the prevalence of AO that was recorded in the 1988 to 1994 period. To our knowledge, this is the first study to describe trends in AO in the three predominant U.S. ethnic groups. This is also the first investigation to use the new proposed WC cut-off point for obesity recommended by the NIH expert panel on the identification, evaluation, and the treatment of overweight and obesity to assess the three U.S. ethnic groups (18) These series of surveys represent the best available data because the sampling schemes were similar and representative of the national population. The training program and quality control measures instituted in the surveys give an added credibility to the data. An important limitation of this study, however, is that the data are inadequate for determining the causes of the relatively quick increase in the prevalence of AO as defined by WC cut-off points. Our study showed increases in WC in white and black men and women and Mexican-American men in 1999 to 2000 compared with 1988 to 1994. The distribution of WC shifted to the right (higher values) in 1999 to 2000 for each of the three ethnic groups that were investigated. The shift to the right was greater in women than men. The result of this investigation showed overall higher prevalences of AO in the 1999 to 2000 study period in white and black men and women. The greatest difference in the overall prevalence of AO between men and women was observed among blacks, with values of 39.4% in the 1988 to 1994 and 38.7% in the 1999 to 2000 study periods. There was no increase between the study periods in prevalences of AO in 40- to 59-year-old Mexican-American men and overall and age-specific categories studied in Mexican-American women. The shifts in the distribution of WC to higher values and overall increases in AO for each of the three ethnic groups in men and women (except Mexican-American men 40 to 49 years old and all Mexican-American women) are consistent with those using BMI as the marker for obesity. The age-adjusted prevalence of obesity using BMI increased from 22.9% in NHANES III (1988 to 1994) to 30.5% in 1999 to 2000 (34). The overall increase in the prevalence of AO in 1999 to 2000 compared with 1988 to 1994, despite voluminous data in epidemiological and clinical journals since NHANES III regarding the negative effects of obesity, may be explained by public health inability to publicize ill effects of obesity (35). Arguably, the lack of decrease in AO may also be attributed to the short time periods between surveys. Disease changes caused by public health interventions are often associated with much larger time periods (in excess of the

3460 1067 924 1469

3023 827 830 1376

n

⬍0.001

90.1 ⫾ 14.8 83.7 ⫾ 15.0 91.8 ⫾ 15.0 93.6 ⫾ 12.9

⬍0.001

97.8 ⫾ 12.5 91.6 ⫾ 12.6 99.6 ⫾ 12.7 100.5 ⫾ 11.1

NH white

2378 1227 677 478

1968 947 543 478

n

⬍0.001

93.7 ⫾ 16.5 89.5 ⫾ 16.5 98.0 ⫾ 16.0 98.2 ⫾ 14.5

⬍0.001

92.5 ⫾ 14.7 88.7 ⫾ 14.8 95.0 ⫾ 14.1 97.3 ⫾ 14.7

NH black

Values are mean values for waist circumference (cm) ⫾ SD. NH, non-Hispanic.

ⱖ20 20 to 39 40 to 59 ⱖ60 Test for linearity

ⱖ20 20 to 39 40 to 59 ⱖ60 Test for linearity

Age (years)

NHANES III, 1988–1994

2133 1148 532 453

2139 1106 531 496

n

⬍0.001

92.0 ⫾ 14.3 88.0 ⫾ 14.3 96.0 ⫾ 12.7 97.5 ⫾ 12.8

Women

⬍0.001

95.0 ⫾ 12.4 90.3 ⫾ 11.9 97.0 ⫾ 11.9 99.9 ⫾ 11.1

Men

Mexican American

851 245 246 360

938 276 264 398

n

⬍0.001

92.5 ⫾ 15.5 88.4 ⫾ 16.4 92.9 ⫾ 15.7 95.4 ⫾ 14.1

⬍0.001

100.8 ⫾ 14.3 95.1 ⫾ 15.2 102.6 ⫾ 14.4 103.6 ⫾ 12.3

NH white

407 122 143 127

369 124 122 123

n

⬍0.001

99.0 ⫾ 16.7 94.1 ⫾ 17.3 101.7 ⫾ 16.4 101.1 ⫾ 15.3

⬍0.001

95.8 ⫾ 16.2 90.5 ⫾ 16.4 97.0 ⫾ 16.6 100.1 ⫾ 14.0

NH black

543 177 189 177

531 183 154 198

n

⬍0.001

94.2 ⫾ 14.1 89.5 ⫾ 13.1 95.2 ⫾ 13.9 97.9 ⫾ 14.0

⬍0.001

98.7 ⫾ 12.9 98.6 ⫾ 13.9 99.1 ⫾ 12.2 102.3 ⫾ 11.3

Mexican American

NHANES 2000, 1999–2000

Table 1. Overall and age-specific waist circumference in white, black and Hispanic adults, 1988 –2000

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Figure 1: Distribution of WC in white, black, and Mexican-American adults from 1988 through 2000.

12 years between NHANES III and NHANES 1999 to 2000). Other investigators believe that the low rate of physician counseling about exercise and nutrition for obesity may, in part, be associated with the lack of significant decrease in overall adiposity (36). Reasons for decrease in AO among Mexican-American women of all ages and Mexican-American men 40 to 49 years old are not clear and warrant further studies. The contribution of AO to cardiovascular diseases and to racial/ethnic differences in cardiovascular disease risks is well known (3,37,38). In our previous study using NHANES III data, we showed that 24%, 39.9%, and 15.7% of type 2 diabetes in white, black, and Hispanic women, respectively, could have been avoided if AO were absent (3). We also showed that AO accounted for 12.1% and 9.8% of racial/ethnic differences in the risk of type 2 diabetes between white and black women and between white and Hispanic women, respectively (3). Also, compared with whites, black men and women had 1.58 and 1.39 times, respectively, the increased risk for development of hyper1014

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tension if they had high values of AO (37). Similarly, clustering of insulin resistance syndromes associated with AO occurred significantly more often in blacks or Hispanics compared with whites (38). Metabolic abnormalities caused by AO start in childhood (39). Fifty percent of obese children remain obese when they grow up (40), and they develop insulin resistance syndromes such as hypertension, glucose intolerance, dyslipidemia, and hyperinsulinemia in adolescence and young adulthood (41). These facts have important implications for early prevention and management of insulin resistance syndromes. Conclusion This study demonstrates a clear increase in AO between 1988 and 2000 despite increased understanding of the need for screening and treatment for obesity. With the exception of Mexican-American women, AO is increasing in all three U.S. ethnic groups that were evaluated in this study. Obesity preventive measures should target high-risk groups. Future

47.3 30.6 53.2 66.2

(1.1) (1.2) (1.3) (0.9)

63.5 46.9 73.6 75.7

24.1 15.6 26.5 34.9

(1.1) (0.8) (1.4) (1.2)

(0.9) (1.1) (1.2) (1.1)

Percentage (SE)

NH black

63.8 46.3 73.9 77.7

30.0 14.6 40.0 40.5

(1.1) (1.2) (1.1) (0.9)

(1.1) (0.8) (1.1) (0.8)

Percentage (SE)

MA

53.6 42.4 59.7 67.8

39.3 15.7 46.2 51.3

(1.1) (1.3) (1.2) (1.4)

(1.2) (1.4) (1.3) (1.2)

Percentage (SE)

NH white

(1.3) (1.1) (1.2) (1.4)

70.5 58.3 78.3 78.7

(1.2) (1.3) (1.2) (1.1)

Women

31.8 23.4 33.6 43.1

Men

Percentage (SE)

NH black

62.1 45.8 70.4 76.8

35.5 29.5 32.5 50.5

(1.3) (1.1) (1.3) (1.4)

(1.2) (1.3) (1.2) (1.4)

Percentage (SE)

MA

NHANES 2000, 1999–2000

6.3 (5.1–9.3) 11.8 (8.9–13.2) 6.5 (3.7–8.8) 1.6 (0.5–3.3)

8.2 (5.7–9.9) 9.0 (6.1–11.2) 7.9 (6.3–9.7) 6.9 (4.4–8.7)

Percentage (95%CI)

NH white

7.0 (5.4–9.5) 11.4 (9.1–15.0) 4.7 (2.2–6.8) 3.0 (1.2–5.8)

7.7 (4.2–11.1) 7.8 (5.9–9.9) 7.1 (4.8–5.2) 8.2 (6.1–9.5)

Percentage (95%CI)

NH black

Change, 1988–2000

⫺1.7 (⫺5.2–1.2) ⫺0.5 (⫺2.5–1.8) ⫺3.5 (⫺7.0–3.1) ⫺0.9 (⫺2.7–2.8)

5.5 (2.5–7.5) 14.9 (9.5–16.1) ⫺7.5 (⫺10.–2.2) 10.0 (7.2–13.2)

Percentage (95%CI)

MA

Abdominal obesity was defined as waist circumference of ⱖ102 cm (⬃40 in) in men and ⱖ88 cm (⬃35 in) in women. NHANES III, Third U.S. National Health and Nutrition Examination Survey; NHANES 2000, U.S. National Health and Nutrition Examination Survey of 1999 –2000; NH, non-Hispanic; MA, Mexican American. * Age-adjusted using 2000 U.S. census data employing 20 to 39, 40 to 59, and 60⫹ age groups.

ⱖ20* 20 to 39 40 to 59 ⱖ60

31.1 16.7 38.3 44.4

ⱖ20* 20 to 39 40 to 59 ⬎60

(1.1) (0.9) (1.2) (0.8)

Percentage (SE)

Age (years)

NH white

NHANES III, 1988–1994

Table 2. Prevalence of age-adjusted abdominal obesity in U.S. adults 1988 –2000 by ethnicity

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studies should develop and evaluate evidence-based programs that show promise for long-term health behavior changes to facilitate the prevention of AO and related comorbidities. Such programs should be tailored for use beginning in childhood. The health benefits from decreasing prevalence of AO are vital to public health.

16. 17.

Acknowledgments

18.

This study was partially supported by funds from the Mercer University Physicians Research Network. Data from the NHANES were obtained from the U.S. National Center for Health Statistics.

19.

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