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Physical Activity and the Metabolic Syndrome in a Tri-ethnic Sample of Women Melinda L. Irwin,* Barbara E. Ainsworth,†‡ Elizabeth J. Mayer-Davis,† Cheryl L. Addy,† Russell R. Pate,‡ and J. Larry Durstine‡

Abstract IRWIN, MELINDA L., BARBARA E. AINSWORTH, ELIZABETH J. MAYER-DAVIS, CHERYL L. ADDY, RUSSELL R. PATE, AND J. LARRY DURSTINE. Physical activity and the metabolic syndrome in a tri-ethnic sample of women. Obes Res. 2002;10:1030 –1037. Objective: To determine the association of moderate-intensity physical activity (PA), vigorous-intensity PA, and maximal treadmill duration with the metabolic syndrome among African-American (n ⫽ 49), Native-American (n ⫽ 46), and white (n ⫽ 51) women (ages, 40 to 83 years), enrolled in the Cross-Cultural Activity Participation Study. Research Methods and Procedures: The metabolic syndrome was defined as three or more of the following risk factors: waist circumference ⬎88 cm, blood pressure ⱖ130/85 mm Hg, fasting glucose ⱖ110 mg/dL, hypertriglyceridemia (ⱖ150 mg/dL), and high-density lipoprotein-cholesterol ⬍50 mg/dL. PA was determined from detailed PA records that included all PA performed during two consecutive 4-day periods. Maximal treadmill duration was determined from a graded exercise test. Women were categorized into quartiles of moderate-intensity PA, vigorous-intensity PA, and maximal treadmill duration. Multiple logistic regression was used to estimate odds ratios of the metabolic syndrome as a function of the four PA categories, adjusted for age, ethnicity, study site, menopausal status, and use of hormone-replacement therapy. Results: The adjusted odds ratio for the metabolic syndrome was 0.18 (95% confidence interval, 0.33 to 0.90) for women in the highest category of moderate-intensity PA compared with women in the lowest category (p ⫽ 0.01 for trend).

Received for review December 31, 2001. Accepted for publication in final form July 18, 2002. *Department of Epidemiology and Public Health, Yale University School of Medicine, New Haven, Connecticut, †Department of Epidemiology and Biostatistics, Norman J. Arnold School of Public Health, and ‡Department of Exercise Science, School of Public Health, University of South Carolina, Columbia, South Carolina. Address correspondence to Melinda L. Irwin, PhD, MPH, Department of Epidemiology and Public Health, Yale University School of Medicine PO Box 208034, New Haven, CT 06520-8034. E-mail: [email protected] Copyright © 2002 NAASO

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Similar associations were observed for the metabolic syndrome with vigorous-intensity PA (p ⫽ 0.01 for trend) and maximal treadmill duration (p ⫽ 0.0004 for trend). Discussion: Higher levels of moderate and vigorous-intensity PA and greater maximal treadmill duration were inversely associated with the metabolic syndrome among an ethnically diverse sample of women. Key words: race, fitness, cardiovascular disease, Syndrome X, insulin-resistance syndrome

Introduction The metabolic syndrome is highly prevalent in the United States (1). Approximately 24% of United States adults have the syndrome defined as a combination of three or more risk factors for cardiovascular disease (CVD) including central obesity, hypertriglyceridemia, high blood pressure, high fasting glucose, and decreased high-density lipoproteincholesterol (HDL-C) (1). People with the metabolic syndrome are at increased risk for CVD and mortality from CVD and all-causes (2). Weight management and achieving appropriate levels of physical activity (PA) may provide a comprehensive strategy toward prevention and/or treatment of the metabolic syndrome (3,4). Numerous mechanisms may contribute to a protective effect of PA on the metabolic syndrome. Higher levels of PA and cardiorespiratory fitness have favorable effects on individual risk factors of the metabolic syndrome (5– 8). PA also directly improves insulin sensitivity by increasing the number and activity of glucose transporters in both muscle and adipose tissue (7,8). To our knowledge, only two studies have examined the association between PA or cardiorespiratory fitness levels and the metabolic syndrome (3,4). In one study, higher PA and cardiorespiratory fitness levels were associated with a decrease in clustering of three or more risk factors associated with the metabolic syndrome in 711 white middle-aged men (3). Similar inverse associations between cardiorespiratory fitness and clustering of

Physical Activity and the Metabolic Syndrome, Irwin et al.

metabolic risk factors were also observed in a large cohort (n ⫽ 19,436) of middle-aged men and women of higher socioeconomic status (4). Less is known about the association among PA, fitness levels, and the metabolic syndrome in women of different ethnicities. Further, whereas most studies generally show that vigorous-intensity PA may reduce risk factors for the metabolic syndrome and CVD, these results are not directly applicable to most women who do not regularly perform such vigorous-intensity PA, nor are the results consistent with the current moderate-intensity PA recommendation (9). The net result is a general lack of a solid research database regarding the association among PA of varying intensities, cardiorespiratory fitness levels, and the metabolic syndrome among women of varying ethnicities. We therefore investigated the association among PA, specifically moderate-intensity PA and vigorous-intensity PA, maximal treadmill duration, and the metabolic syndrome in a tri-ethnic sample of women.

Research Methods and Procedures Subjects Subjects were participants in the Cross-Cultural Activity Participation Study, a 5-year community study designed to identify PA patterns among minority women ⬎40 years of age (7,10). A total of 57 African-American women residing in South Carolina, 50 Native-American women residing in Pueblo and Navajo reservations in New Mexico, and 53 white women residing in South Carolina (n ⫽ 28) and New Mexico (n ⫽ 25) were recruited into the study with newspaper advertisements, radio advertisements, and personal conversations. Study inclusion criteria consisted of the following: 1) age 40 years or older; 2) self-identified ethnicity as African American, non-Hispanic white, or at least 50% Native American; 3) absence of physical illnesses or disabilities that would limit daily physical activities such as walking; and 4) the ability to read and write well enough to record daily physical activities in a record book. Subjects gave written informed consent for participation in research as approved by Institutional Review Boards of the University of South Carolina and the University of New Mexico. Subjects were given $50 for successful completion of the study. Among the 160 women enrolled in the study, 13 had incomplete PA data and one was taking insulin medication. After excluding these 14 subjects, 146 women were eligible for the analyses. Study Design Data collection and testing procedures were standardized through preliminary training sessions at a common site for all field and laboratory staff. The same study procedures and models of laboratory equipment were used at each site to obtain study data. All data were entered and analyzed at the University of South Carolina (Columbia, South Carolina).

Study Data Surveys. Interviewer-administered surveys designed to obtain demographic and health behavior information were administered to each subject. Ethnicity was obtained from the demographic survey and reported as 100% African American, 100% non-Hispanic white, or at least 50% Native American. PA Records. PA records from four consecutive days were collected twice, 1 month apart, to obtain a detailed account of all PA performed. PA recordings began when subjects awoke in the morning until they went to bed in the evening. For each activity, subjects recorded the duration, purpose and type, and perceived intensity of the activity in the PA record. PA records were edited for completeness and clarity by study staff in the presence of the subjects. The study staff assigned a five-digit code obtained from the Compendium of Physical Activities (11) for all activities recorded in the PA record that linked the purpose, description, and metabolic-equivalent (MET) intensity for each activity. The MET intensity reflects the associated metabolic rate for a specific activity divided by a standard resting metabolic rate. Individual differences that may alter the energy cost of movement (i.e., body mass) are not taken into account. Therefore, PA was measured in terms of absolute intensity rather than relative intensity. PA data were summed as minutes per day and METminutes per day, computed as the product of the minutes for each activity by the MET intensity level. One MET-minute is roughly equivalent to 1 kcal/min for a 60-kg person (12). Minutes/day and MET-minutes/day of activity were sorted into intensity groups using the Centers for Disease Control and Prevention–American College of Sports Medicine recommendations for moderate (3 to 6 METs) and vigorous (⬎6 METs) intensity activities (9). Maximal Treadmill Duration. Maximal treadmill duration was determined from the subject’s time to exhaustion on a treadmill graded exercise test. The graded exercise test was performed under physician supervision using a Quinton treadmill (Quinton, Inc., Bothell, MA) with a three-channel electrocardiogram (ECG) monitor (Quinton, Inc.). A treadmill protocol designed for this study was pilot tested to assure that all study subjects could reach volitional fatigue within 26 minutes. The treadmill protocol started at 2.0 mph and 0% grade (2.5 METs) and increased every 2 minutes to the maximum speed and grade of 3.7 mph and 21% grade (14.5 METs). Exercise-test endpoints were exhaustion, dyspnea, ECG abnormalities, or equipment technical problems (13). All subjects reached volitional fatigue with no ECG abnormalities or equipment technical problems. Blood Pressure. A mercury column sphygmomanometer (Baumanometer Desk Top model no. 320; W.A. Baum Co., Copiague, NY) was used to measure blood pressure. Subjects were seated quietly for 20 minutes before measurements were taken. Blood pressure was taken two OBESITY RESEARCH Vol. 10 No. 10 October 2002

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times on the right arm with subjects sitting with legs uncrossed using standardized methods recommended by the American Heart Association (14). The average of two systolic and diastolic blood pressure measures was recorded for data entry and analysis. Body Mass Index. To determine body mass index (BMI) [weight (kilograms) divided by height (meters squared) (2)], body weight was measured to the nearest 0.1 kg using a Seca Model 770 scale (Shorr Productions, Olney, MD), and height was measured to the nearest 0.1 inch using a stadiometer (Seca model) and converted to meters. The average of the two readings for weight and height were recorded for data entry and analysis. Central Obesity. Central obesity was measured according to waist circumference using a Gulick anthropometric tape measure (Creative Health Products, Plymouth, MI) at the minimum waist circumference (under clothing and next to the subject’s skin). Waist circumference was measured twice to the nearest 0.1 cm at the end of exhalation. The average measurement was recorded for data entry and analysis. Blood Analyses. Subjects fasted for 12 hours before resting blood samples were collected from the antecubital vein using standard venipuncture methods. Plasma insulin levels were determined by radioimmunoassay using the Coat-ACount Insulin procedure (Diagnostic Products Corporation, Los Angeles, CA) (15). HDL-C was measured spectrophotometrically using a stable Liebermann-Burchard reagent. HDL-C was determined with the manganese chloride procedure (16). Triglyceride concentrations were determined using enzymatic kits from Sigma Diagnostics (St. Louis, MO). Fasting glucose levels were determined using enzymatic kits from Sigma Diagnostics. The Metabolic Syndrome. The recently released Adult Treatment Panel III report (17) was used to define the metabolic syndrome as a combination of any three or more of the following metabolic risk factors: central obesity (waist circumference ⬎88 cm), high blood pressure (ⱖ130/85 mm Hg), or use of anti-hypertensive medication, high fasting glucose (ⱖ110 mg/dL), hypertriglyceridemia (ⱖ 150 ml/dL), and low HDL-C (⬍50 ml/dL). We have used this definition of the metabolic syndrome in our analyses. Statistical Analyses The following dimensions of PA and cardiorespiratory fitness were considered: 1) moderate-intensity PA, which included all types of PA (i.e., recreational, household, and occupation), requiring 3 to 6 METs; 2) vigorous-intensity PA, which included all types of PA requiring ⬎6 METs; and 3) maximal treadmill duration (minutes and METs) as an indirect measure of cardiorespiratory fitness. Women were categorized into approximate quartiles (using indicator 1032


variables) of moderate-intensity PA, vigorous-intensity PA, and maximal treadmill duration. Generalized linear models were used with least-square means to determine significant differences in demographic and metabolic variables by ethnicity. Multiple logistic regression was used to estimate odds ratios (ORs) of the metabolic syndrome as a function of the four categories of PA adjusted for other potential confounders including age, ethnicity, study site, menopausal status, and use of hormone-replacement therapy (␣ ⬍ 0.05). ORs were estimated relative to the first quartile (least active). To prevent confounding by vigorous-intensity PA, analyses of moderateintensity PA were conducted among the women who reported no vigorous-intensity PA (n ⫽ 91). Lastly, we investigated whether the association of PA with the metabolic syndrome differed by ethnicity. To test whether the association differed, an interaction term between PA and ethnicity was added to the multiple logistic regression model (i.e., the metabolic syndrome as a function of the four categories of PA adjusted for age, ethnicity, study site, menopausal status, and use of hormone-replacement therapy; ␣ ⬍ 0.20). All data were analyzed using PC-SAS software (SAS Institute, Cary, NC).

Results Demographic and metabolic characteristics of the study sample are presented in Table 1. Native-American women were slightly younger (51 ⫾ 2 years) than African-American women (57 ⫾ 2 years) and white women (56 ⫾ 2 years). African-American women had a higher BMI (31.0 ⫾ 0.8 kg/m2) compared with Native-American women (28.6 ⫾ 0.8 kg/m2) and white women (25.1 ⫾ 0.8 kg/m2) (p ⬍ 0.05). African-American women had the highest prevalence of central obesity (53%) and hypertension (71%), whereas Native-American women had the highest prevalence of high glucose levels (20%), hypertriglyceridemia (28%), and low HDL-C (54%). Table 2 shows the age-adjusted prevalence of cumulative metabolic risk factors for the metabolic syndrome by ethnicity. The metabolic syndrome, defined as a combination of any three or more metabolic risk factors, was evident in 27% of this cohort. The prevalence of the metabolic syndrome was highest in Native-American women (37%) compared with African-American women (33%) and white women (12%). On average, the subjects participated in 111 min/d of moderate-intensity PA and 5 min/d of vigorous-intensity PA (Table 3). Native-American women reported participating in significantly more moderate-intensity PA (146 ⫾ 9 min/d) than African-American women (79 ⫾ 9 min/d) and white women (110 ⫾ 9 min/d) (p ⬍ 0.05). Maximal treadmill duration was highest among white women (15.4 ⫾ 0.4 minutes) compared with African-American women (10.7 ⫾ 0.5 minutes) and Native-American women (13.9 ⫾ 0.6 minutes).


Table 1. Demographic and metabolic characteristics (mean ⫾ SE) of study participants by ethnicity

Age (years) Education (years) Weight (kg) Height (cm) BMI (kg/m2) Waist circumference (cm) Systolic BP (mm Hg) Diastolic BP (mm Hg) Glucose (mg/dL) Triglycerides (mg/dL) HDL-C (mg/dL) Centrally obese‡ (%) High BP§ (%) High fasting glucose¶ (%) Hypertriglyceridemia㛳 (%) Low HDL-C** (%)

African Americans (n ⴝ 49)

Native Americans (n ⴝ 46)

Whites (n ⴝ 51)

All (n ⴝ 146)

56.7 ⫾ 1.5 15.2 ⫾ 0.4 82.5 ⫾ 2.1 163.2 ⫾ 0.9 31.0 ⫾ 0.8 88.9 ⫾ 1.7 129.1 ⫾ 2.4 79.5 ⫾ 1.3 93.7 ⫾ 4.1 86.5 ⫾ 8.3 64.9 ⫾ 2.2 53 71 16 4 18

51.4 ⫾ 1.6* 14.9 ⫾ 0.4 71.0 ⫾ 2.2* 157.7 ⫾ 0.9* 28.6 ⫾ 0.8* 88.7 ⫾ 1.7 118.9 ⫾ 2.5* 76.7 ⫾ 1.3 94.7 ⫾ 4.2 131.1 ⫾ 8.6* 50.7 ⫾ 2.3* 46 41* 20 28* 54*

55.5 ⫾ 1.5 16.1 ⫾ 0.4† 68.2 ⫾ 2.1* 164.9 ⫾ 0.8† 25.1 ⫾ 0.8*† 77.8 ⫾ 1.7*† 117.4 ⫾ 2.4* 76.2 ⫾ 1.3 85.4 ⫾ 4.0 108.9 ⫾ 8.2 57.5 ⫾ 2.2*† 16*† 39* 2*† 18* 27†

54.6 ⫾ 0.9 15.4 ⫾ 0.2 73.9 ⫾ 1.3 162.1 ⫾ 0.6 28.2 ⫾ 0.5 85.0 ⫾ 1.1 121.8 ⫾ 1.5 77.5 ⫾ 0.7 91.1 ⫾ 2.4 108.3 ⫾ 5.0 57.9 ⫾ 1.4 38 38 12 16 33

* Significantly different from African Americans ( p ⬍ 0.05). † Significantly different from Native Americans ( p ⬍ 0.05). ‡ Centrally obese: waist circumference ⬎88 cm. § High BP: systolic ⱖ 130 mm Hg, diastolic ⱖ 85 mm Hg, taking anti-hypertensive medication. ¶ High fasting glucose: fasting glucose levels ⱖ110 mg/dL or physician-diagnosed type 2 diabetes. 㛳 Hypertriglyceridemia: fasting triglyceride levels ⱖ150 mg/dL. ** Low HDL-C: fasting HDL-C ⬍50 mg/dL. BMI, body mass index; BP, blood pressure; HDL-C, high-density lipoprotein-cholesterol.

Table 4 shows results for the logistic regression of the metabolic syndrome on moderate-intensity PA, vigorousintensity PA, and maximal treadmill duration among all women adjusted for age, ethnicity, study site, menopausal status, and use of hormone-replacement therapy. The prevalence and ORs of the metabolic syndrome was inversely graded across moderate-intensity PA (p ⫽ 0.01), vigorousintensity PA (p ⫽ 0.01), and maximal treadmill duration (p ⫽ 0.0004 for minutes and p ⫽ 0.006 for METs). When examining the association between moderate-intensity PA and the metabolic syndrome, the odds of having the metabolic syndrome was 82% lower among the most active women (ⱖ491 MET-minute/day of moderate-intensity PA) compared with the least active women (⬍216 MET-minute/ day of moderate-intensity PA) [OR ⫽ 0.18; 95% confidence interval (CI), 0.03 to 0.90]. The odds of having the metabolic syndrome was 86% lower among women reporting any vigorous-intensity PA compared with women not reporting any vigorous-intensity PA (OR ⫽ 0.14; 95% CI: 0.02 to 1.20). The odds of having the metabolic syndrome was 93% lower among women in the highest quartile of

maximal treadmill duration (⬎16 minutes) compared with women in the lowest quartile (ⱕ10 minutes) (OR ⫽ 0.07; 95% CI: 0.02 to 0.35). Lastly, the odds of having the metabolic syndrome was 92% lower among women in the highest quartile of maximal treadmill duration in METs (⬎10.5 METs) compared with women in the lowest quartile (ⱕ7.5 METs) (OR ⫽ 0.08; 95% CI: 0.01 to 0.66). The inverse association among moderate-intensity PA, vigorous-intensity PA, and maximal treadmill duration and the metabolic syndrome were similar for each ethnic group (p ⫽ 0.40, 0.80, and 0.25 for interaction, respectively).

Discussion Higher levels of moderate-intensity PA, vigorous-intensity PA, and maximal treadmill duration were inversely associated with clustering of any three or more clinically relevant metabolic risk factors among an ethnically diverse sample of women. Our findings confirm those of Carroll et al. (3) and Whaley et al. (4), which showed inverse associations between higher levels of PA and cardiorespiratory OBESITY RESEARCH Vol. 10 No. 10 October 2002

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Table 2. Age-adjusted prevalence of metabolic risk factors by ethnicity African Americans

Native Americans

Whites

All

Metabolic risk factors* (n)

n

%

n

%

n

%

n

%

None ⱖ1 ⱖ2 ⱖ3 ⱖ4 5

10 39 24 16 1 0

20 80 49 33 2 0

12 34 26 17 8 2

26 74 57 37 17* 4

23 28 15 6 3 0

45†‡ 55†‡ 29†‡ 12†‡ 6 0

45 101 65 39 12 2

31 69 45 27 8 1

* Metabolic risk factors include: high blood pressure (systolic ⱖ 130, diastolic ⱖ 85, or taking anti-hypertensive medications); hypertriglyceridemia (fasting triglyceride level ⱖ 150 mg/dL); decreased high-density lipoprotein-cholesterol (HDL-C) (fasting HDL-C ⬍ 50 mg/dL); high fasting glucose (fasting glucose level ⱖ 110 mg/dL); and central obesity (waist circumference ⬎ 88 cm). † Significantly different from African Americans ( p ⬍ 0.05). ‡ Significantly different from Native Americans ( p ⬍ 0.05).

fitness and clustering of metabolic risk factors among middle-aged white men and women. To our knowledge, no other studies examining the association between varying intensities of PA or fitness and the metabolic syndrome in minority populations have been published. Although all associations (i.e., moderate-intensity PA, vigorous-intensity PA, and maximal treadmill duration with the metabolic syndrome) were statistically significant,

the strongest association was observed between maximal treadmill duration and the metabolic syndrome. Maximal treadmill duration, a proxy of cardiorespiratory fitness, is a more objective, yet indirect, measure of PA. Maximal treadmill duration is therefore a more accurate exposure variable. Over-reporting of PA may occur with PA records, leading to a greater measurement error and a decreased ability to detect significant associations with various health-related

Table 3. Age-adjusted (PA) amount and maximal treadmill duration of study participants by ethnicity

Moderate-intensity PA* Minutes/day MET-minutes/day Vigorous-intensity PA§ Minutes/day MET-minutes/day Maximal treadmill duration Minutes METs

African Americans (n ⴝ 49)

Native Americans (n ⴝ 46)

Whites (n ⴝ 51)

All (n ⴝ 146)

Mean ⴞ SE

Mean ⴞ SE

Mean ⴞ SE

Mean ⴞ SE

79 ⫾ 9 308 ⫾ 35

146 ⫾ 9† 554 ⫾ 36†

110 ⫾ 9†‡ 433 ⫾ 34†‡

111 ⫾ 6 429 ⫾ 22

2⫾1 17 ⫾ 10

5⫾1 37 ⫾ 11

6 ⫾ 1† 48 ⫾ 10†

5⫾2 35 ⫾ 12

10.7 ⫾ 0.5 7.3 ⫾ 0.3

13.9 ⫾ 0.6† 9.0 ⫾ 0.3†

15.4 ⫾ 0.5† 9.7 ⫾ 0.3†

13.4 ⫾ 0.4 8.7 ⫾ 0.2

* Moderate-intensity PA ⫽ 3 to 6 METs. † Significantly different from African Americans ( p ⬍ 0.05). ‡ Significantly different from Native Americans ( p ⬍ 0.05). § Vigorous-intensity PA ⬎ 6 METs. PA, physical activity; MET, metabolic equivalent.

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Table 4. Prevalence (%) and adjusted ORs (OR) within 95% CIs for the metabolic syndrome* across physical activity and maximal treadmill duration quartiles in 146 women Moderate-intensity physical activity (MET-min/d†)

Sample with the metabolic syndrome (%) Adjusted OR‡ (95% CI)

18 to 215 (n ⴝ 23)

216 to 337 (n ⴝ 23)

338 to 490 (n ⴝ 23)

491 to 1351 (n ⴝ 22)

p for trend

39 1.0

43 0.78 (0.21 to 2.92)

30 0.56 (0.13 to 2.35)

18 0.18 (0.03 to 0.90)

0.01

Vigorous-intensity physical activity (MET-min/d§)

Sample with the metabolic syndrome (%) Adjusted OR¶ (95% CI)

0 (n ⴝ 91)

0.1 to 30 (n ⴝ 20)

31 to 119 (n ⴝ 20)

120 to 1351 (n ⴝ 15)

p for trend

33 1.0

25 0.66 (0.20 to 2.16)

15 0.42 (0.11 to 1.63)

7 0.14 (0.02 to 1.20)

0.01

Maximal treadmill duration (minutes)

Sample with the metabolic syndrome (%) Adjusted OR‡ (95% CI)

4.4 to 10.0 (n ⴝ 36)

10.1 to 13.0 (n ⴝ 37)

13.1 to 16.0 (n ⴝ 36)

16.1 to 26.0 (n ⴝ 37)

p for trend

53 1.0

27 0.23 (0.07 to 0.74)

17 0.13 (0.04 to 0.48)

11 0.07 (0.02 to 0.35)

0.0004

Maximal treadmill duration (METs) 4.5 to 7.5 (n ⴝ 57) Sample with the metabolic syndrome (%)

40

7.6 to 8.5 (n ⴝ 32)

8.6 to 10.5 (n ⴝ 34)

10.6 to 14.5 (n ⴝ 23)

25

21

4

p for trend

0.006 Adjusted OR‡ (95% CI)

1.0

0.48 (0.17 to 1.40)

0.37 (0.11 to 1.2)

0.08 (0.01 to 0.66)

* Metabolic syndrome ⫽ three or more metabolic risk factors. † Moderate-intensity PA ⫽ 3 to 6 METs (excluding women who reported vigorous-intensity PA). ‡ Adjusted for age, ethnicity, site, menopausal status, and use of hormone-replacement therapy. § Vigorous-intensity PA ⬎ 6 METs. ¶ Adjusted for age, ethnicity, site, menopausal status, use of hormone-replacement therapy, and moderate-intensity PA. OR, odds ratio; PA, physical activity; MET, metabolic equivalent.

outcomes. In this study, the correlation between maximal treadmill duration and moderate-intensity PA was r ⫽ 0.29 (p ⫽ 0.0004); the correlation between maximal treadmill duration and vigorous-intensity PA was r ⫽ 0.46 (p ⫽ 0.0001). Including measures of both PA and maximal treadmill duration strengthens our findings of significant associations between both PA and treadmill duration and the metabolic syndrome.

The prevalence of high blood pressure (38%) and high glucose levels (12%) in the sample overall were slightly higher than national prevalence rates (29% and 10%, respectively) (1). Conversely, the prevalence of central obesity was slightly lower in our sample (38%) compared with a national prevalence rate of 46% (1). In our sample, African-American women had the highest prevalence of central obesity and high blood pressure, whereas Native-American OBESITY RESEARCH Vol. 10 No. 10 October 2002

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women had the highest prevalence of high glucose levels, hypertriglyceridemia, and low HDL-C. These findings are similar to national prevalence data of minority women having higher prevalence rates of CVD risk factors as compared with white women (1,18 –20). Although the prevalence and specific metabolic risk factors varied across ethnic groups, the PA, maximal treadmill duration, and the metabolic syndrome associations were similar for each ethnic group. This study has some limitations. First, the cross-sectional design of this study precludes the assumption of causality. Second, the overall sample size was small and may not be representative of the respective ethnic groups. Third, there is some debate as to how to accurately define the metabolic syndrome. We chose to define the metabolic syndrome similarly to how it was defined in the recently released Third Report of the National Cholesterol Education Program Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (2). However, other studies have defined the metabolic syndrome differently by including measures of insulin sensitivity or total adiposity. This study also has strengths that contribute to the understanding of PA and the metabolic syndrome in women. First, we included equal numbers of African-American, Native-American, and white women in our study. Second, PA was measured using PA records kept by the subjects for 8 days. A total of 66,091 observations of daily PA were written into the PA records, averaging ⬃60 total activities per person per day. Because we asked the subjects to record every type of activity in their PA record (including household, occupational, and recreational activities), our mean levels of moderate-intensity PA are higher (111 min/d) than other studies that only assessed recreational types of activities. However, our findings are similar to estimates from studies that assessed all types of PA, suggesting women spend significant parts of their day in occupational, household, and family care activities and less time in recreational and conditioning activities (21). Furthermore, the PA records used in this study have been validated against doubly-labeled water in a sample of middle-aged men of mainly non-Hispanic white ethnicity (83% of the sample) (22). A Pearson correlation coefficient of r ⫽ 0.32 and 8% relative difference in mean daily energy expenditure was observed between the PA records and doubly-labeled water. The same type of PA records were used for both the validity study and the present study. The number of activities (range of 10 to 90) recorded in the PA records in the validity study was also similar to the number of activities recorded in the present study. In conclusion, rates of obesity and physical inactivity are high; as of 2001, ⬎50% of US adults were overweight or obese and only 15% met the recommended minimum level of moderate-intensity PA (9,18). This study indicates that higher levels of moderate-intensity PA, vigorous-intensity PA, and greater maximal treadmill duration are inversely 1036


associated with the metabolic syndrome among an ethnically diverse sample of women. Studies with larger sample sizes examining the association between different types of moderate-intensity PA and the metabolic syndrome among ethnically diverse men and women are necessary to confirm the results of this study.

Acknowledgments This study was supported by a grant awarded to Dr. Barbara E. Ainsworth (NIH WHI-SIP No. 22W-U48/ CCU409664). This article fulfills a partial requirement for a Ph.D. dissertation by M.L. Irwin. References 1. Ford E, Giles W, Dietz W. Prevalence of the metabolic syndrome among US adults. JAMA. 2002;287:356 –9. 2. Trevisan M, Liu J, Bahsas F, Menotti A. Syndrome X and mortality: a population-based study. Am J Epidemiol. 1998; 148:958 – 66. 3. Carroll S, Cooke C, and Butterly R. Metabolic clustering, physical activity and fitness in nonsmoking, middle-aged men. Med Sci Sports Exerc. 2000;32:2079 – 86. 4. Whaley M, Kampert J, Kohl H, et al. Physical fitness and clustering of risk factors associated with the metabolic syndrome. Med Sci Sports Exerc. 1999;31:287–93. 5. American College of Sports Medicine Position Stand. Physical activity, physical fitness, and hypertension [Review]. Med Sci Sports Exerc. 1993;25:i-x. 6. Durstine, J, Haskell W. Effects of exercise training on plasma lipids and lipoproteins. In: Holloszy JO, ed. Exercise and Sport Science Reviews. Baltimore, MD: Williams & Wilkins; 1994, pp. 477–521. 7. Irwin, M, Mayer-Davis E, Addy C, et al. Moderate intensity physical activity and fasting insulin levels in women: the Cross Cultural Activity Participation Study. Diabetes Care. 2000;23:449 –54. 8. Mayer-Davis E, D’Agostino R, Karter A, et al. Intensity and amount of physical activity in relation to insulin sensitivity. The Insulin Resistance Atherosclerosis Study. JAMA. 1998; 279:669 –74. 9. Pate R, Pratt M, Blair S, et al. Physical activity and public health. A recommendation from the CDC and ACSM. JAMA. 1995;273:402–7. 10. Ainsworth, B., Irwin M, Addy C, et al. Moderate physical activity patterns among minority women: The Cross Cultural Activity Participation Study. J Womens Health. 1999;8:805–13. 11. Ainsworth B, Haskell W, Whitt M, et al. Compendium of physical activities: an update of activity codes and MET intensities. Med Sci Sports Exerc. 2000;32:S498 –S516. 12. Taylor H, Jacobs D, Schucker B, et al. A questionnaire for the assessment of leisure time physical activities. J Chron Dis. 1978;31:741–55. 13. American College of Sports Medicine. Guidelines for Exercise Testing and Prescription. Philadelphia, PA: Lea & Febiger; 1991, pp. 72–3. 14. National Institutes of Health. The fifth report of the Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure. NIH Publication, No. 93-1088. Bethesda, MD: National Institutes of Health, NHLBI; 1993.


15. Tietz N, ed. Fundamentals of Chemistry. Philadelphia: W.B. Saunders Co .; 1988, pp. 496 – 8. 16. Warnick G, Albers J. A comprehensive evaluation of the heparin-manganese precipitation procedure for estimation high density lipoprotein. J Lipid Res. 1978;19:65–76. 17. National Institutes of Health. Third report of the National Cholesterol Education Program Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III). NIH Publication, No. 01-3670. Bethesda, MD: National Institutes of Health; 2001. 18. Centers for Disease Control and Prevention. Prevalence of obesity: behavioral risk factor surveillance system, United States, 1998. MMWR Morb Mortal Wkly Rep; 1998;256 –59. 19. Centers for Disease Control and Prevention. Prevalence of

hypertension: behavioral risk factor surveillance system, United States, 1998. MMWR Morb Mortal Wkly Rep; 1998; 123–127. 20. Geiss L, Herman W, and Smith P. Mortality in non-insulin dependent diabetes. Diabetes in America. NIH Publication, No. 95-1468. Washington, DC: National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases; 1995, pp. 233–57. 21. Weller I, Corey P. The impact of excluding non-leisure energy expenditure on the relation of physical activity and mortality in women. Epidemiology. 1998;9:632–5. 22. Conway JM, Seale JL, Jacobs Jr. DR, Irwin ML, Ainsworth BE. Comparison of energy expenditure estimates from doubly labeled water and physical activity questionnaires and records. Am J Clin Nutr. 2002;75:519 –25.


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