Trends in Overweight among

Transcription

1 Trends in Overweight among US Adults from 1987 to 1993: A Multistate Telephone Survey Deborahl A. Galuska, PhD, MPH, Mart Serdula, MD, MPH, Elsie Pamulk, PhD, Palul Z. Siegel, MD, and Tim Bvers, MD, MPH Introduction Obesity increases the risk of many chronic health conditions, including hypertension, type II diabetes. hypercholesterolemia, gallbladder disease. osteoarthritis, and some cancers.i'2 Despite the wellpublicized consequences of obesity and a flourishing weight-loss industry, the prevalence of overweight in the United States increased during the 1980s.3-7 Data of measured weights and heights, collectcd from the National Health and Nutrition Examination Surveys (NHANES), indicated that between NHANES 11 (1976 to 198(0) and phase I of NHANES III (1988 to 1991), the proportion of overweight adults in the United States increased from 25.4%' to 33.3 C. Development of effective strategies to reverse this trend in the prevalence of overweight rcquires an understanding of its demographic and behavioral determinants. Researchers have hypothesized that the trcnd may reflect a declinc in the level of physical activity3a or in the prevalence of smoking.' We analyzed data from the Behavioral Risk Factor Survcillance System (BRFSS) from 1987 to 1993 to (1) determine if the increase in the prevalence of overweight, previously described through the period 1988 to 1991, continued through 1993: (2) identifv population subgroups for which the magnitude of the increase was larger; and (3) determine to what extent trends in leisure-time physical activity and smoking might have accounted for the trends in overweight. Methods Studv Popullation The BRFSS is an ongoing monthly telephone survey of the health behaviors of US adults. The data are collected by state health departments in collaboration with the Centers for Disease Control and Prevention. The objective of the BRFSS is to provide state-specific prevalence estimates of health behaviors and practices associated with the leading causes of death among adults in the United States.,8 For each year and in each participating state, an independent probability sample of adults in the noninstitutionalized. civilian population is selected by random-digit dialing with the use of a multistage cluster sampling design primarilv based on the Waksberg method.9 All states use an identical core questionnaire, which trained interviewers administer on the telephone in approximately 25 minutes. Thirtv-two states and the District of Columbia participated in the BRFSS survey cach year from 1987 through The median state cooperation rate (the ratio of completed interviews to the sum Deborah A. Galuska and Marv Serdula (and Tim Byers at the time of this study) are with the Division of Nutrition and Physical Activity, and Paul Z. Siegel is with the Division of Adult and Community Health, National Center of Chronic Disease Prevention and Health Promotion. Centers for Disease Control and Prevention. Atlanta. Ga; at the time of the study, Dr Galuska was also an Epidemic Intelligence Service fellow. Elsie Pamuk is with the Office of Analysis and Epidemiology. National Center for Health Statistics. Hvattsville, MD. Dr Byers is currently with the Department of Preventive Medicine and Biometrics. University of Colorado School of Medicine, Denver. Requests for reprints should be sent to Deborah A. Galuska. PhD. Division of Nutrition and Physical Activity. NCCDPHP (K126), Centers for Disease Control and Prevention, 4770 Buford Hwv NE. Atlanta. GA This paper was accepted February American Journal of Public Health 1729

2 Galuska et al. TABLE 1-Demographic and Behavioral Characteristics of Participants In the Behavioral Risk Factor Surveillance System, 1987, 1990, and 1993 of completed interviews and refusals) ranged from 81% in 1993 to 85% in Definition ofoverweight During the interview, participants were asked to report their weight and height (without shoes). These values were used to calculate a body mass index (weight in kilograms divided by height in meters squared). Overweight was defined as a body mass index of at least 27.8 for men and 27.3 for women. Severe overweight was defined as a body mass index of at least 3 for men and 32.3 for women. These classifications were based on the 85th and 95th percentile values for body mass index among US adults aged 20 to 29 years in NHANES (n =47 372), % (n =56 564), % (n =64 974), % Sex Male Female Age,y Race White Black Hispanic Other Marital status Never married Previously married Currently married Education < high school High school Some college College degree Region West Midwest South Northeast Smoking status Never smoker Former smoker Current smoker Leisure-time activity status Sedentary a Irregular a Regular a Note. Percentages may not add to 100 because of rounding. aestimates are calculated for 1992 because leisure-time activity data were not collected in Subgroups Sex-specific trends in overweight were examined within subgroups defined by demographic and behavioral factors. The demographic characteristics were age, race/ethnicity, educational level, marital status, and region of residence (West [Arizona, California, Hawaii, Idaho, Montana, New Mexico, Utah, and Washington], South [Alabama, Florida, Georgia, Kentucky, Maryland, Missouri, North Carolina, South Carolina, Tennessee, Texas, West Virginia, and the District of Columbia], Midwest [Illinois, Indiana, Minnesota, Nebraska, North Dakota, Ohio, South Dakota, and Wisconsin], and Northeast [Maine, Massachusetts, New Hampshire, New York, and Rhode Island]). Two behavioral characteristics that are related to body weight-smoking and leisure-time physical activity-were examined. Smoking behavior was characterized as current, former, and never. After participants were asked to report the time spent engaged in their two most frequent leisure-time activities in the previous month, leisure-time physical activity was categorized as sedentary (no leisure-time physical activity during the previous month), irregular (cumulative time less than 20 minutes per session or less than three times per week), and regular (cumulative time greater than or equal to 20 minutes per session at least three times per week).1' Because not all states collected data on physical activity in 1993, analyses that include physical activity are reported only through Analytic Population From 1987 to 1993, persons from the 33 states participated in the BRFSS. Sample sizes per year ranged from in 1987 to in 1993; sample sizes per state per year ranged from 1050 to Of the total number of persons surveyed, (93.2%) were included in this analysis. Reasons for exclusion were current pregnancy (1.3%), or missing/invalid information on weight or height (3.2%) or on any of the covariates (2.3%). Data Analysis Sex-specific estimates of the prevalence of overweight were calculated for each subgroup in each year. State census information on race/ethnicity, age, and sex were used to weight prevalence estimates for the state-specific probabilities of selection and nonresponse. Estimates were also directly age standardized to the overall population distribution for all 33 states in 1987 in this BRFSS sample. The weights were defined as 18 to 29 years (0.2261), 30 to 39 years (0.2374), 40 to 49 years (0.1544), 50 to 59 years (0.1199), 60 to 69 years (0.1342), and 70+ years (0.1280). All prevalence estimates and their standard errors were calculated with the use of SUDAAN, an analysis program that takes into account complex sampling designs.'2 The absolute increase in the prevalence of overweight was defined as the difference between the age-adjusted prevalence in 1993 and the age-adjusted prevalence in To evaluate whether trends in overweight were a linear func American Journal of Public Health

3 Trends in Overweight TABLE 2-Age-Adjusted,a Sex-Specific Prevalence of Overweight or Severe Overweight among Participants, by Year, in the Behavioral Risk Factor Surveillance System, 1987 through 1993 Year, % 95% Cl Overall Annual Annual Increase, %b Increase, %c Increased Men Overweighte , Severe overweightf , 0.6 Women Overweightg , Severe overweighth , 0.5 aadjusted to the age distribution of the 1987 Behavioral Risk Factor Surveillance System population. bprevalence of overweight (1993) - prevalence of overweight (1987). cbeta coefficient for weighted least squared linear regression model: prevalence of overweight = a +,3 dconfidence interval (Cl) for beta coefficient. ebody mass index fbody mass index gbody mass index. 3. hbody mass index (year). tion of time, weighted least squares linear regression was used with year as the independent variable (range = 87 to 93), the age-adjusted prevalence of overweight was used as the dependent variable, and weights were computed as the inverse of the estimated variance of the prevalence.t3 The beta coefficient from the linear models was used to estimate the annual increase in the prevalence of overweight. The standard error for each beta coefficient was calculated as the inverse square root of the weighted sum of squared deviations of the variable year from that its weighted mean.14 The linear trend in overweight was considered significant at ( =.05 if the 95% confidence interval for the beta coefficient did not include 0. Plots of the prevalence estimates suggested that the increase in the prevalence of overweight in the later period of observation might be more than that in the earlier period. Therefore, the trend in overweight was also modeled with a second-order polynomial response function. The independent variable, year, was expressed as a deviation from its mean to avoid problems in multicollinearity.13 All regression analyses were completed with the use of SAS, Version 6.15 Results A description of the population in 3 selected years is shown in Table 1. In all 3 years, respondents (about 50% men) were predominantly White and married. About one half reported some college education, and about one third resided in southern states. Most were nonsmokers, and about TABLE 3-Sex-Specific Body Mass Index (BMI) for Selected Percentiles, Behavioral Risk Factor Surveillance System, 1987, 1990, and 1993 two thirds reported at least some leisuretime physical activity. Did the Prevalence of Ovenveight Continue to Increase through 1993? From 1987 to 1993, the age-adjusted prevalence of overweight increased from 21.9% to 26.7% among men and from 20.6% to 25.4% among women (Table 2). When the prevalence of overweight was regressed on year, year accounted for 87% of the total variation in the prevalence of overweight for both men and Percentile Men Year Overall change in BMI Overall change in weight, kga Women Year Overall change in BMI Overall change in weight, kgb achange for a m (5'9") man. bchange for a m (5'4") woman. women. Linear regression indicated that the prevalence of overweight rose similarly for men and women at approximately % per year. A second-order polynomial function showed some acceleration in the rate of the increase over time; the P value associated with the quadratic term was moderately significant for both men and women (.02 < P <.05). The prevalence of severe overweight also increased over time. Between 1987 and 1993, the age-adjusted prevalence of severe overweight rose from 6.5% to 9.4% American Journal of Public Health 1731

4 Galuska et al. TABLE 4-Age-Adjusted,a Sex-Specific Prevalence of Overweight among Participants In the Behavioral Risk Factor Surveillance System, by Demographic and Behavioral Characteristics, 1987 through 1993 Year, % Overall Annual 95% Cl Increase, %b Increase, %c Annual Increased Overall Crude Age adjusted Age, y Race White Black Hispanic Other Marital status Never married Previously married Currently married Education < high school High school degree Some college College degree Region West Midwest South Northeast Smoking status Never Former Current Leisure-time activity status Sedentary Irregular Regular Men e 4.7e 4.1 e ,, 0.5, 0.5, , 0.5, , , 0.6,, , , , ,1.6, , ,1.4, , 0.3, 0.3, 0.6,, , 0.6, , 0.0, 0.3, ,1.4 Overall Crude Age adjusted Age, y Race White Black Hispanic Other Marital status Never married Previously married Currently married Women ,,, , , , , 0.2, 0.6, 0.4, , , , , , (Continued) 1732 American Journal of Public Health

5 Trends in Overweight TABLE 4-Continued Year, % Overall Annual 95% Cl Increase, %b Increase, %c Annual Increased Education <high school ,1.4 High school degree ,1.5 Some college ,1.4 College degree ,1.3 Region West ,1.5 Midwest , South ,1.3 Northeast ,1.4 Smoking status Never ,1.4 Former ,1.3 Current , Leisure-time activity status Sedentary e 0.6,1.6 Irregular e 0.5,1.5 Regular e 0.4, aadjusted to the age distribution of the 1987 Behavioral Risk Factor Surveillance System population. bprevalence of overweight (1993) - prevalence of overweight (1987). cbeta coefficient for weighted least squared linear regression model: prevalence of overweight = a +, (year). dconfidence interval (Cl) for beta coefficient. eestimates are calculated for 1992 because leisure-time activity data were not collected in for men and from 5.9% to 7.9% for women. This was an increase of 0.5% per year and 0.4% per year, respectively. In 1989, the prevalence of overweight appeared to decrease slightly for both men and women. We could not determine if this decline was real or an unexplained anomaly of data collection in However, the decline was not caused by a large decrease in the prevalence of overweight in one or two subgroups of the population, as most subgroups reported a decrease. The increased prevalence of overweight appears to reflect both an overall shift in the distribution of weight in the population and a tendency for overweight persons to be heavier (Table 3). The body mass index increased for all percentiles of the distribution, but the increase was more substantial at the upper end. For example, for both men and women, the change at the 70th percentile was approximately twice that at the 30th percentile. Over the 7-year period, the increase in the median body mass index represents an increase of kg and 1.9 kg for averageheight men and women, respectively. Were There Population Subgroups for Which the Magnitude ofthe Increase in the Prevalence of Overweight Was Larger? The trend toward increased overweight between 1987 and 1993 was observed in all demographic subgroups (Table 4); statistically significant increases were observed in most subgroups. (A complete table of prevalence estimates for each year will be provided by the authors upon request.) For men, the absolute increase in the prevalence of overweight ranged from % to 8.7% while the estimated annual increase ranged from 0.4% to 1.5% per year. The greatest annual increases were observed for men who were Black (1.5% per year) and men who lived in the Northeast (1.4% per year). For women, there was less variability in the increase in the prevalence of overweight among subgroups. With the exception of the category of "other" for race/ethnicity, the absolute increase in the prevalence of overweight in subgroups ranged from 2.0% to 6.6% while the estimated annual increase ranged from 0.5% to % per year. Did Alterations in Smoking or in Leisure-TimeActivity LevelAccount for the Increased Prevalence of Overweight? Between 1987 and 1993, the prevalence of smoking declined 3.1% (Table 1). This decline may have accounted for some of the 5% increase in overweight. However, although smokers were less likely to be overweight in most years, the increasing prevalence of overweight was observed in all subgroups defined by smoking status (Table 4). Between 1987 and 1992, the prevalence of sedentary leisure-time behavior declined 2.4% (Table 1). This trend is counter to that expected to explain an increase in overweight. Although the sedentary were most likely to be overweight at any time, the prevalence of overweight increased in all subgroups defined by leisure-time activity status (Table 4). To explore whether the relatively higher annual increases in the prevalence of overweight experienced by Black men and men living in the Northeast could be explained by differential changes in smoking or physical activity, we compared changes in these behaviors within these subgroups with changes experienced by all men. Potentially, some of the increase in overweight in Black men could be explained by a relatively large decline in smoking. The age-adjusted decrease in the prevalence of current smokers was 3.1% for all men and 7.3% for Black men. However, smoking declined by only 2.1% for men living in the Northeast. Changes in physical activity could not account for the increase in overweight in these two subgroups. For all men, the age-adjusted prevalence of sedentary activity declined American Journal of Public Health 1733

6 Galuska et al. 2.9%, while it declined 3.9% for Black men and 4.9% for those living in the Northeast. Discussion Our analysis indicates that the increase in the prevalence of overweight, previously documented through the period 1988 to 1991,3-7 continued through 1993 potentially at an accelerated rate. Between 1987 and 1993, the absolute increase in the prevalence of overweight was approximately 5%. The prevalence of overweight increased in all subgroups of the population. In interpreting these observations, we must consider several points. The prevalence of overweight in the BRFSS is calculated from self-reported weights and heights. Because overweight men and women tend to underestimate their weight'6'7 whereas all members of the population tend to overestimate their height,'6"8 the prevalence estimates of overweight are likely to be low.'9 Under the assumption that the biases in selfreport remain constant over time, the observed trends are likely to reflect real changes. However, we could not test this assumption. Because the BRFSS includes only persons with telephones, selection bias could also lead to conservative estimates of the prevalence of overweight. Those without phones are of lower socioeconomic status,2' which is a factor associated with overweight."' Also of concern is the refusal of some of those contacted to participate in the interview (median = 15% to 19%, depending on survey year), as well as the specific refusal of some participants to respond to the weight question (approximately 3% overall). However, the direction of this bias cannot be predicted because the actual weights and heights of these nonrespondents cannot be determined. Despite these limitations, the increase in the prevalence of overweight over the first half of the observation period for this analysis (1987 to 1990) is consistent with national data indicating that the prevalence of overweight increased throughout the 1980s.4- Data from the National Health Interview Survey, which is also based on self-reported weights and heights, show that the prevalence of overweight (defined as 120% or more of the ideal body weight) rose from 21.6% in 1983, to 24.0% in 1985, to 27.5% in Results from national surveys using measured weights and heights indicate that between NHANES II and phase I of NHANES III, the prevalence of overweight in persons 20 to 74 years old increased by 7.9%.4 This increase over the approximate 12-year observation period is similar to the 1.8% increase observed during the first 4 years of the BRFSS survey (% vs 0.5% average increase per year, respectively). This body of information, which documents a rise in the prevalence of overweight, is supplemented by data from the BRFSS, which extend the observation period through 1993 and raise the possibility that the increase in overweight among adults is accelerating. Our analyses indicate that, consistent with trends in the 1980s,4 the increase has continued to occur for all demographic subgroups. Of particular concern are the upward trends in those subgroups already at high risk of overweight-in particular, middle-aged men and Hispanic and Black women. Despite the considerable time and money spent promoting weight loss in the United States, the upward shift in weight appears to be most substantial among those who are already overweight and hence are at highest risk for weightrelated morbidity and mortality.2 This finding is consistent with observations by Shah et al.7 that weight increases among a Midwestern population in the 1980s occurred primarily among men and women in the upper ends of the weight distribution. Our analysis cannot fully delineate the reasons for this increase in overweight. Because current smokers weigh less than nonsmokers and those who quit smoking tend to gain weight after quitting,22 the 3.1% decline in smoking over the period covered by this analysis could explain part, but not all, of the 5% increase in overweight. However, the upward trend in overweight occurs in all three smoking categories in the BRFSS data, even in those who had never smoked. In support of these results, Shah et al.7 found that the increase in overweight in their midwestern population was unaltered after they controlled for a decline in smoking. Decreased energy expenditure could account for the increased prevalence of overweight. However, in the BRFSS, the proportion of people reporting sedentary leisure-time physical activity actually decreased by 2.4% between 1987 and Although leisure-time physical activity does not account for all physical activity and information on activity during work was not obtained on the BRFSS interview, it seems unlikely that changes in work-related physical activity could account for all of the observed increases in body weight. National Health Interview Surveys conducted in 1985 and 1990 suggest that changes in work-related physical activity would be relatively small: people's perception of whether their job or main daily activity required at least a moderate amount of physical activity remained unchanged over this period for both men and women.3 Increased energy intake in the population could partially explain an increasing prevalence of overweight. Unfortunately, data on fat and caloric consumption were not collected as part of the BRFSS. Numerous recent studies72425 and a review26 have suggested that the consumption of fat has either declined or remained unchanged in the past several decades, but this may not reflect a decline in total caloric consumption. Findings from NHANES, based on dietary reports from 24-hour recalls, suggest that although the proportion of calories from fat decreased from 36% to 34% between NHANES II and phase I of NHANES III, the total energy consumed increased by 100 to 300 kcal.24 While this finding may be an artifact caused by changes in dietary assessment methods between the two surveys, it is also possible that persons may truly be compensating for a reduction in fat consumption with an increase in the amount of calories consumed. Neither these nor other analyses provide satisfactory explanations for the increase in overweight. However, the widespread increase in the prevalence of overweight suggests that adverse changes in energy consumption and/or expenditure have occurred in the American population. Identifying behaviors that have contributed to this increased prevalence of overweight in the United States will be necessary for developing effective intervention strategies. Better answers may be found by exploring changes in behaviors not easily captured by common dietary and activity measurement tools. For example, relevant factors in diet may include the frequency and timing of food consumption, and frequency and quality of meals eaten away from home. Relevant factors in energy expenditure may include transportation patterns, household work, or time spent in inactivity such as watching television and sitting at a computer workstation. In summary, the BRFSS data indicate that the increase in the prevalence of overweight in US adults, previously docu American Journal of Public Health

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