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Centers for Disease Control and Prevention, 4770 Buford Highway, NE, Mailstop K66, Atlanta, GA 30341. E-mail: Cokoro@cdc.gov
Objectives: To examine the association between body weight and disability among persons with and without self-reported arthritis.
Research Methods and Procedures: Data were analyzed for noninstitutionalized adults, 45 years or older, in states that participated in the Behavioral Risk Factor Surveillance System. Self-reported BMI (kilograms per meter squared) was used to categorize participants into six BMI-defined groups: underweight (<18.5), normal weight (18.5 to <25), overweight (25 to <30), obese, class 1 (30 to <35), obese, class 2 (35 to <40), and obese, class 3 (≥40).
Results: Class 3 obesity (BMI ≥ 40) was significantly associated with disability among participants both with and without self-reported arthritis. The adjusted odds ratio (AOR) for disability in participants with class 3 obesity was 2.75 [95% confidence interval (CI) = 2.22 to 3.40] among those with self-reported arthritis and 1.77 (95% CI = 1.20 to 2.62) among those without self-reported arthritis compared with those of normal weight (BMI 18.5 to <25). Persons with self-reported arthritis who were obese, class 2 (BMI 35 to <40) and obese, class 1 (BMI 30 to <35) and women with self-reported arthritis who were overweight (BMI 25 to <30) also had higher odds of disability compared with those of normal weight [AOR = 1.72 (95% CI = 1.47 to 2.00), AOR = 1.30 (95% CI = 1.17 to 1.44), and AOR = 1.18 (95% CI = 1.06 to 1.32), respectively].
Discussion: Our findings reveal that obesity is associated with disability. Preventing and controlling obesity may improve the quality of life for persons with and without self-reported arthritis.
Disability affects an estimated 53 million persons in the United States (1). Direct medical costs associated with disability reached $260 billion in 1996 (2). Arthritis, a leading cause of disability, limits activity for over 7 million U.S. adults (2, 3). As the population ages and the prevalences of disability and arthritis increase, the annual disability-related costs to the U.S. health care system are expected to increase to over $283 billion (4), and the annual arthritis-related costs are expected to increase to over $190 billion (5).
The Centers for Disease Control and Prevention (CDC)1 reported that obesity has become an epidemic in the United States (6). In 1999–2000, 31% of U.S. adults were obese (BMI ≥ 30) and 34% were overweight (BMI 25.9 to 29.9) (7). Excess body weight is a well-established risk factor for several types of arthritis including osteoarthritis (OA), rheumatoid arthritis, and gout (8, 9, 10, 11, 12, 13, 14). Not only is excess weight a primary risk factor for the development of arthritis (8, 14, 15, 16), but it also increases the risk for disease progression (15, 17) and disability among people with arthritis (15, 17, 18). In addition, people with lower extremity mobility disabilities are 2.5 times more likely to be obese than those without such disabilities (19).
The primary purpose of this study was to investigate the association between body weight and disability among persons with and without self-reported arthritis, using data from the 2001 Behavioral Risk Factor Surveillance System (BRFSS). A secondary aim was to identify gender differences in these relationships.
Research Methods and Procedures
The BRFSS is a cross-sectional telephone survey operated by state health agencies with assistance from the CDC. The primary purpose is to provide state-specific estimates of behaviors that relate to the leading causes of death in the U.S. The survey uses a multistage cluster design based on random-digit dialing to select a representative sample of U.S. adults 18 years or older who are not institutionalized. Data from all states are pooled to produce nationally representative estimates. A detailed description of the survey methods is available elsewhere (20). All BRFSS questionnaires, data, and reports are available at www.cdc.govbrfss. In 2001, a total of 203, 021 persons completed the BRFSS interview in all 50 states and the District of Columbia.
Persons who had a disability were defined as respondents who answered “yes” to either one of two questions: “Are you limited in any way in any activities because of physical, mental, or emotional problems?” or “Do you now have any health problem that requires you to use special equipment, such as a cane, a wheelchair, a special bed, or a special telephone?” Persons for whom responses to both questions were missing, “don't know,” or “refused” were excluded from the analysis.
Persons with chronic joint symptoms (CJS) were defined as respondents who answered “yes” to two questions: “During the past 12 months, have you had pain, aching, stiffness, or swelling in or around a joint?” and “Were these symptoms present on most days for at least 1 month?” Persons with doctor-diagnosed arthritis were defined as respondents who answered “yes” to the question, “Have you ever been told by a doctor that you have arthritis?” To be classified as having self-reported arthritis, respondents must have reported either CJS or doctor-diagnosed arthritis.
Self-reported weight and height were assessed by asking, “About how much do you weigh without shoes?” and “About how tall are you without shoes?” We calculated BMI (kilograms per meter squared) on the basis of self-reported weight and height. Participants were classified as underweight (<18.5); normal weight (18.5 to <25); overweight (25 to <30); obese, class 1 (30 to <35); obese, class 2 (35 to <40); and obese, class 3 (≥40) (21).
A current smoker was defined as someone who had smoked at least 100 cigarettes and was currently smoking. A former smoker was defined as someone who had smoked at least 100 cigarettes but was no longer smoking. A nonsmoker was defined as someone who had never smoked 100 cigarettes. Respondents were asked six questions about their participation in moderate or vigorous physical activity during a usual week. Regarding moderate physical activity, persons were asked the following: “Now, thinking about the moderate physical activities you do in a usual week, do you do moderate activities for at least 10 minutes at a time, such as brisk walking, bicycling, vacuuming, gardening, or any other activity that causes small increases in breathing or heart rate?” For vigorous physical activity, persons were asked “Now, thinking about the vigorous physical activities you do in a usual week, do you do vigorous activities for at least 10 minutes at a time, such as running, aerobics, heavy yard work, or any other activity that causes large increases in breathing or heart rate?” For each type of activity, respondents indicated the number of days per week and the total time per day they participated in the activity for at least 10 minutes at a time. Current federal guidelines recommend at least 30 minutes of moderate physical activity on 5 or more days per week or at least 20 minutes of vigorous physical activity on 3 or more days per week (22, 23). Consistent with these guidelines, respondents were classified into three levels of physical activity: inactive, no physical activity; insufficient activity, some, but not at recommended levels; and recommended activity, those who met either the moderate physical activity recommendation (at least 30 minutes of moderate intensity physical activity at least 5 days per week) or the vigorous recommendation (at least 20 minutes of vigorous intensity at least 3 days per week). Self-rated health was assessed by asking respondents, “Would you say that, in general, your health is excellent, very good, good, fair, or poor?” Other chronic conditions assessed were diabetes, asthma, hypertension, and hypercholesterolemia.
We calculated odds ratios (ORs) and 95% confidence intervals (CIs) to assess the association between BMI and disability among persons with and without self-reported arthritis. We then used logistic regression analysis to adjust these ORs for potential confounders (sex, age, race or ethnicity, education, marital status, smoking status, physical activity, and chronic conditions besides arthritis). SUDAAN (24) was used in all analyses to account for the complex sampling design.
There were 105, 509 BRFSS respondents 45 years and older. We excluded those with missing data for disability (n = 2051), weight or height (n = 4588), arthritis (n = 599), and other covariates (n = 16, 484). The remaining 81, 787 respondents (40, 777 with self-reported arthritis and 41, 010 without self-reported arthritis) were included in the analyses. To determine whether the exclusion of survey participants with missing data may have created a selection bias, we also compared the distribution of demographic variables (sex, age, race or ethnicity, marital status) among those excluded from the analyses with that of those included to confirm that there were no important differences.
Compared with respondents without self-reported arthritis, those with self-reported arthritis were more likely to be disabled (41% vs. 12%), to be limited in their activities (37% vs. 10%), and to require the use of special equipment (16% vs. 4%). Among persons both with and without self-reported arthritis, disability prevalence was highest for those who were underweight or obese, class 3; had less than a high school education; were previously married; were physically inactive; and smoked (Table 1), as well as for those who were unable to work, unemployed, or retired, those who self-reported fair or poor health, and those who had one or more chronic condition other than arthritis.
Table 1. Prevalence of disability among U.S. adults 45 years and older, stratified by self-reported arthritis status, for selected characteristics, 2001*
Self-reported arthritis (n = 40, 777)
No self-reported arthritis (n = 41, 010)
Data are based on self-reports; Ns, unweighted; percentages are weighted. Respondents reporting either CJS or doctor-diagnosed arthritis were classified as having self-reported arthritis.
Recommended, moderate physical activity for ≥30 minutes per session, ≥5 times per week, or vigorous activity for ≥20 minutes per session, ≥3 times per week; insufficient, some physical activity but not for recommended duration or frequency; inactive, no physical activity.
For each BMI category, persons with self-reported arthritis had a higher prevalence of disability than those without self-reported arthritis (underweight, 52.2% vs. 21.5%; normal weight, 34.9% vs. 10.5%; overweight, 37.6% vs. 11.0%; obese, class 1, 45.0% vs. 14.0%; obese, class 2, 54.1% vs. 16.1%; obese, class 3, 66.9% vs. 20.9%) (Table 1). For those with self-reported arthritis, the direct age-adjusted prevalence of disability was nonlinearly related to BMI (roughly J or U shaped), whereas those without self-reported arthritis experienced a much more gradual increase in disability (increased variability occurred at the extremes of BMI) (Figure 1).
Selected Characteristics by BMI
Compared with respondents of normal weight, those in the obese, class 3 category tended to be younger and were more likely to have less than a high school education; to be black (non-Hispanic) or Hispanic; to have never been married; and to be unable to work (data not shown). They were also more likely to be physically inactive, to self-report fair or poor health, to have additional chronic diseases other than arthritis, and not to currently smoke. In all BMI categories, persons with self-reported arthritis were more likely to be women. However, those without self-reported arthritis who were overweight or obese, class 1 were more likely to be male, and those who were obese, class 2 were equally likely to be of either sex.
Risk Factors for Disability
As shown in Table 2, after adjusting for potential confounding factors, we found that among persons with self-reported arthritis, those who were obese, class 3 were 2.75 (95% CI = 2.22 to 3.40) times more likely to be disabled than were those of normal weight and that, among those without self-reported arthritis, those who were obese, class 3 were 1.77 (95% CI = 1.20 to 2.62) times more likely to be disabled. This difference was noted for both men (adjusted OR [AOR] = 2.40, 95% CI = 1.63 to 3.54) and women (AOR = 3.04, 95% CI = 2.36 to 3.91) with self-reported arthritis, as well as for women without self-reported arthritis (AOR = 2.24, 95% CI = 1.33 to 3.78).
Table 2. Prevalence and adjusted odds ratios for disability by BMI among U.S. adults 45 years and older, stratified by sex and self-reported arthritis status, 2001
Self-reported arthritis (n = 40, 777)
No self-reported arthritis (n = 41, 010)
Self-reported arthritis (n = 26, 460)
No self-reported arthritis (n = 22, 005)
Self-reported arthritis (n = 14, 317)
No self-reported arthritis (n = 19, 005)
Adjusted for age, sex, race or ethnicity, education, marital status, smoking status, physical activity, and number of chronic diseases (other than arthritis).
Adjusted for age, race or ethnicity, education, marital status, smoking status, physical activity, and number of chronic diseases (other than arthritis).
Among persons with self-reported arthritis, those who were obese, class 2 were 1.72 (95% CI = 1.47 to 2.00) times more likely to be disabled than were those of normal weight. This difference was noted for both men (AOR = 1.45, 95% CI = 1.12 to 1.88) and women (AOR = 1.93, 95% CI = 1.59 to 2.33) with self-reported arthritis.
Persons with self-reported arthritis who were obese, class 1 were also more likely to be disabled than those of normal weight (AOR = 1.30, 95% CI = 1.17 to 1.44). When men and women were analyzed separately, a significant association persisted for women with and without self-reported arthritis (AOR = 1.45, 95% CI = 1.28 to 1.65 and AOR = 1.63, 95% CI = 1.23 to 2.16, respectively). Furthermore, women with self-reported arthritis who were overweight were at higher odds of disability than those of normal weight (AOR = 1.18, 95% CI = 1.06 to 1.32).
Among persons who were underweight, both those with and without self-reported arthritis were at higher odds of disability than those of normal weight (AOR = 1.66, 95% CI = 1.27 to 2.17 and AOR = 1.89, 95% CI = 1.36 to 2.63, respectively).
The results of our study, an analysis of data from the largest telephone survey in the world, revealed that among U.S. residents 45 years and older, body weight is associated with disability. Regardless of their self-reported arthritis status, survey participants who were underweight or obese were more likely to be disabled than participants of normal weight. We also found that among women with self-reported arthritis, those who were overweight were more likely than those of normal weight to be disabled.
Previous research has documented that a host of debilitating health problems are associated with obesity, including chronic musculoskeletal problems (25). These debilitating and typically painful conditions usually occur before the development of chronic, life-threatening health problems such as cardiovascular disease, diabetes, and some cancers (6, 26, 27). Obesity has also been associated with the development of OA and gout and with knee pain among obese middle-aged women during or past menopause (8, 9, 10, 11, 12, 13). The prevalence of obesity-related knee OA has also been shown to be particularly high among blacks (28).
Although this study did not allow us to determine whether obese participants with a disability became obese before or after the onset of disability, other studies have shown obese persons to be at increased risk for disability (29, 30, 31). For example, Rissanen et al. found most people receiving disability pensions for obesity-related disabilities had cardiovascular or musculoskeletal diseases, and, among women, one-quarter of all disability pensions for these diseases were solely attributable to overweight and obesity (29). Furthermore, Launer et al. reported that high BMI is a strong predictor of long-term risk for mobility disability in older women (30).
The results of this study are consistent with the findings of these previous studies. Specifically, we found a strong association between self-reported arthritis and disability as BMI increased. In addition, regardless of arthritis status, persons at extreme BMI levels were significantly more likely to be disabled than those of normal weight. These findings are particularly troubling given the increasing prevalence of class 3 obesity among adults, almost 3-fold between 1990 and 2000 (32). Furthermore, these extreme BMI levels are associated with the most severe health consequences (27, 32, 33, 34, 35) and have the potential to reverse several decades of declines in disability and institutionalization (36, 37).
Our finding that being underweight is associated with disability is also consistent with findings from a study by Verbrugge et al. (17). Those authors surmised that people with numerous chronic conditions are very ill and that very ill people tend to lose weight (17). Additional analyses performed by Verbrugge et al. revealed that underweight has negligible association with disability among healthy people but, instead, that underweight and disability are coexisting outcomes of severe illness (17).
This study has at least five limitations. First, because BRFSS excludes institutionalized persons and those without telephones, as well as those unable to complete the survey because of hearing or speech impairments, lack of stamina, or an inability to get to the phone, our findings probably underestimate the true prevalence of disability in the U.S. Second, because the BRFSS relies on self-reported data not confirmed by a physician, our results could be influenced by reporting biases of various sorts. For example, because overweight participants, especially women, in self-reported studies tend to underestimate their weight and because all participants tend to overestimate their height, the true percentage of persons who were overweight is likely to be higher than our data showed (38, 39). Third, the case definition of self-reported arthritis might include some persons with injuries rather than arthritis. Fourth, because adjustment could not be done for all possible chronic conditions (e.g., cardiovascular disease, cancer) or recent weight loss, we could not analyze further the association we found between BMI and disability. And fifth, because our study was cross-sectional, we could not determine cause and effect.
Our findings demonstrated that obesity was associated with a significant likelihood of disability, both among people with self-reported arthritis and among those without. Furthermore, among women with arthritis, being overweight was also associated with disability. For people who are overweight, weight loss may prevent arthritis (8, 14, 15, 16), delay its progression, and prevent or reduce disability (15, 17). Other strategies such as physical activity, medications, and self-care can reduce the pain, lack of mobility, and disability experienced by persons with arthritis (40, 41, 42, 43, 44, 45). Comorbid conditions, such as cardiovascular disease and diabetes, frequently present in persons with arthritis may also be ameliorated by these strategies (40, 41). Programs such as the Arthritis Foundation's People with Arthritis Can Exercise and the Arthritis Self-Help Course have been shown to reduce the impact of arthritis and promote physical activity and good nutrition (46). Other interventions that target persons who are overweight or obese, especially those with arthritis or lower extremity disabilities, should also be developed. Underweight persons, principally those who are very ill, may need specific interventions designed to build and maintain muscle mass and strength. Our findings of a strong association between weight and disability among U.S. adults 45 years and older call for more focus on obesity prevention in our health system. Through prevention efforts, we may be able to improve the quality of life and increase the number of years of healthy life among U.S. adults.
There was no outside funding/support for this study. We thank the state BRFSS coordinators for their help in collecting the data used in this analysis and the members of the Behavior Surveillance Branch for their assistance in developing the database.