Functional limitation is a major factor in medical costs. This study was undertaken to evaluate the prevalence of functional limitation among adults with arthritis and the frequency of functional decline over 2 years, and to investigate factors amenable to public health intervention that predict functional decline.
Longitudinal data (1998–2000) from a cohort of 5,715 adults ages 65 years or older with arthritis from a national probability sample were analyzed. Function was defined based on ability to perform basic activities of daily living (ADL) tasks and instrumental ADL. Adjusted odds ratios (ORs) from a multiple logistic regression model were used to estimate the associations between functional decline and comorbid conditions, health behaviors, and economic factors.
Overall, 19.7% of this cohort had functional limitation at baseline, including 12.9% with ADL limitations. Over the subsequent 2 years, function declined in 13.6% of those at risk. Functional decline was most frequent among women (15.0%) and minorities (18.0% Hispanics, 18.7% African Americans) with arthritis. Lack of regular vigorous physical activity, the most prevalent risk factor (64%), almost doubled the odds of functional decline (adjusted OR 1.9, 95% confidence interval 1.5–2.4) after controlling for all risk factors. It was found that if all subjects engaged in regular vigorous physical activity, the expected functional decline could be reduced as much as 32%. Other significant predictors included older age, cognitive impairment, depressive symptoms, diabetes, physical limitations, no alcohol use, stroke, and vision impairment.
High economic, societal, and personal costs from functional limitation among older adults make the prevention of functional problems an important public health issue (1–3). Medical spending among the elderly is related more closely to the presence of functional limitation than to remaining life expectancy (4, 5). In 1999, more than 44 million Americans had 1 or more conditions that resulted in a limitation of life activities (6), and in 1996, direct medical costs for persons with disability exceeded $260 billion (6). Arthritis and other rheumatic conditions (hereinafter called arthritis) are leading causes of disability in the US (6). Arthritis affects almost 60% of persons ages 65 years and older (7), of whom more than 1 in 10 report activity limitations (8). By 2010, almost 40 million Americans ages 65 years or older are projected to have arthritis (9), potentially escalating the numbers of older adults with functional impairments.
An understanding of risk factors related to functional decline is essential to the development of population-based public health programs to help maintain functional ability and prevent limitation among older adults with arthritis. While population-based longitudinal studies have investigated risk factors for functional decline, they have not been specific to persons with arthritis (10–12). The literature on functional limitation in arthritis includes a wealth of cross-sectional studies but few longitudinal studies (13, 14), and even these have not been based on national samples.
The present study addressed 3 questions with regard to functional limitation among persons with arthritis ages 65 years and older: 1) What is the frequency with which members of this cohort experience functional task limitations? 2) What is the magnitude of 2-year functional decline among persons at risk? 3) What factors amenable to intervention are the strongest predictors of functional decline? These questions were addressed using longitudinal data from the 1998 Health and Retirement Study (HRS). The HRS is a national probability sample, facilitating findings that represent the national experience. Identification of comorbidities, health behaviors, and/or economic factors that may reduce functional decline in persons ages 65 years and older with arthritis is important for addressing economic and personal costs in this high-risk disability group whose medical costs are largely covered by public insurance via Medicare.
PATIENTS AND METHODS
This study received exemption from Human Subjects Review by the Northwestern University Institutional Review Board for these analyses of public data. The study analyzed national public data on adults with arthritis ages 65 years and older. The data were from the 1998 HRS, a probability sample of US adults who are interviewed biennially (15). The HRS is sponsored by the National Institute on Aging and conducted by the University of Michigan, and is described in detail elsewhere (16). Estimates of the prevalence of functional limitation were based on the cohort of 5,715 respondents ages 65 years and older who had arthritis. Analyses on risk factors for functional decline were restricted to the 4,922 arthritis cohort members at risk of decline whose function was ascertained at the subsequent 2000 interview.
Baseline (1998) arthritis was determined from an affirmative response to the question, “Have you ever had or has a doctor ever told that you have arthritis or rheumatism?” Self-reported arthritis is relevant from a public policy perspective because many persons with arthritis do not see a health care provider for their symptoms (17); thus, measurement of the full burden of arthritis often relies on self-reported data.
We used the Institute of Medicine's classification of functional limitation (18), which defines functional limitation as the inability to carry out functional tasks at the personal level. Functional limitations are defined in terms of basic activities of daily living (ADL) tasks and higher-level instrumental ADL (IADL). IADL tasks included preparing hot meals, shopping for groceries, making telephone calls, taking medications, and managing money. ADL tasks included walking across a room, dressing, bathing, eating, using the toilet, and transferring from a bed. A limitation in a specific IADL or ADL task expected to last 3 months or longer is ascertained from affirmative responses to questions regarding avoidance, inability, or receipt of help or use of equipment to perform the task. Functional limitation in 1998 and 2000 was classified as either none, mild (IADL limitation only), moderate (1–2 ADL limitations), or severe (≥3ADL limitations). This categorization parallels the definition used by Mor and colleagues (19). Functional decline was identified by 2-year progression to a more severe level of functional limitation, to capture substantial change in a person's ability to function independently.
Demographic characteristics recorded included race/ethnicity, age, sex, and marital status. HRS race/ethnicity information was used to classify people into 3 mutually exclusive groups: non-Hispanic African American, Hispanic, and non-Hispanic white/other.
Comorbid health conditions at baseline were assessed from self-reported information. Chronic health conditions were ascertained from self-reports of physician diagnosis of conditions that included cancer, diabetes, heart disease (heart attack, coronary artery disease, angina, and congestive heart failure), hypertension, pulmonary disease (chronic bronchitis, emphysema, not including asthma), or stroke. The presence of depressive symptoms was determined by an abbreviated Center for Epidemiologic Studies Depression Scale (CES-D) assessment (20). For analysis purposes, the presence of depressive symptoms was defined as a report of 1 or more nonsomatic CES-D mood items (felt depressed, not happy, felt lonely, did not enjoy life, felt sad), consistent with work by Stump and colleagues (21), to avoid confounding somatic depressive symptoms with arthritis-related symptoms. Cognitive status was based on a summary measure from response to tests indicating 4 types of mental ability: a modified version of the Telephone Interview for Cognitive Status, tests of immediate and delayed verbal recall, and Serial 7's test (22). Scores from these individual measures were combined into a single summary measure of cognitive function scaled from 0 to 35, ranging from lower to higher ability. Using the practice of HRS researchers, respondents scoring 8 or less on the summary measure were classified as having moderate to severe cognitive impairment (22). Obesity was defined as body mass index (BMI) ≥30 (weight [kg]/height [m2]), calculated from self-reported height and weight. Low weight was defined as BMI <18.5 (23). Vision impairment was based on the report of having poor vision or being legally blind.
Since severity of disease was not assessed in the HRS, a surrogate for disease/arthritis severity based on limitations in physical activities was used in sensitivity analyses. The presence of physical limitations was assessed from reports of avoidance of walking several blocks, climbing several flights of stairs without resting, pushing or pulling large objects, or lifting or carrying weights >10 pounds or an inability to perform these tasks.
Health behavior factors included smoking, alcohol consumption, regular vigorous physical activity, and weight change. Smoking was ascertained based on a positive response to the question, “Do you smoke cigarettes now?” Alcohol use was based on an affirmative answer to, “Do you ever drink any alcoholic beverages such as beer, wine, or liquor?” Regular vigorous physical activity was ascertained based on a positive response to, “On average, over the last 12 months have you participated in vigorous physical activity or exercise 3 times a week or more? By vigorous physical activity, we mean things like sports, heavy housework, or a job that involves physical labor.” Weight change 2 years prior to baseline or since the previous HRS interview (1995–1996) was characterized as gain of ≥10 pounds, loss of ≥10 pounds, or stable. Weight change was imputed as stable in subjects for whom weight change information was not available (2.3% of the arthritis cohort). Sensitivity analyses omitting these subjects produced virtually identical results.
Economic access factors included education, wealth, family income, and health insurance. Education, a measure of human capital, was dichotomized as ≥12 versus fewer completed years of education. For analysis purposes, family income (all sources received by the respondent and spouse/partner during the preceding year) and wealth were dichotomized using the lowest 1998 HRS population-weighted quartiles of $16,800 and $44,800, respectively. If only partial income or wealth information was provided, dichotomized values were based on imputed estimates developed at the University of Michigan (24). Health insurance information distinguished private insurance holders from those relying solely on Medicare, Medicaid, and other government health insurance (e.g., insurance through the Veterans Administration).
The HRS is a national probability sample. All analyses used person-weights, strata, and sampling error codes for the 1998 HRS data developed at the University of Michigan (25) to provide valid inferences to the US population. SUDAAN software (26) was used in all analyses to account for the complex HRS sampling design and the arthritis subset analyzed. All statistical testing was done at a nominal 5% α significance level.
Prevalence estimates of functional limitation were based on a cohort of 5,715 persons ages 65 years and older interviewed in the 1998 HRS who had self-reported arthritis and for whom baseline information was available. Another 609 persons with proxy interviews were handled as 1998 HRS nonrespondents. For analysis purposes, an additional 6 persons with missing baseline functional information and 53 with insufficient data on baseline covariates were omitted from the analyses. To make statements about 2-year functional decline, we limited these analyses to 4,922 members of the 1998 arthritis cohort at risk of decline who lived at least 2 years following the 1998 interview, excluding by design 180 persons reporting severe baseline limitation (in ≥3 ADL) and 366 who had died. For analysis purposes, 239 nonrespondents to the 2000 HRS and 8 with missing followup information on function were also omitted from analyses of function.
We adjusted for potential bias due to missing interview information and/or nonresponse by handling respondents with complete data as an additional sampling stage to obtain adjusted sampling weights, using standard sampling methodology (27). The adjusted sampling weight for arthritis cohort members equaled the 1998 HRS sampling weight multiplied by the inverted probability of being in the study cohort given the following characteristics: age, sex, race/ethnicity, an incomplete interview, Spanish language, proxy or phone interview, designated respondent, education level, withholding permission for access to additional records, changed residence, number of children, chronic diseases, nonresponse to sensitive questions, negative interview attitude, and geographic region. That probability was estimated using logistic regression.
Direct standardization methods (27) were used to illustrate the potential mediating effect of a risk factor on functional decline. This approach averages the expected functional decline probabilities across the cohort members based on the estimated multiple logistic model given the actual characteristics of each person (comorbidities, health behaviors, economic resources, demographics) but without the target risk factor.
To determine the relative effect of risk factors on functional decline, demographics, comorbidities, health behaviors, and economic resource factors were simultaneously included in a multiple logistic regression model. Based on this inclusive model, those risk factors with the highest adjusted odd ratios (ORs) are the strongest predictors of functional decline relative to other investigated risk factors.
Baseline characteristics of the 5,715 members of the 1998 HRS arthritis cohort ages 65 years and older are shown in Table 1. This population of Medicare-age persons with arthritis was primarily female (64.2%) and included 8.6% African Americans and 4.5% Hispanics. More than 87.8% of this cohort reported having 1 or more comorbid health conditions. Comorbid health conditions were more frequent among minorities (African Americans 93.8%, Hispanics 93.1%) than whites/others (86.9%). The most prevalent single risk factor for functional decline was lack of regular vigorous physical activity, reported by 64.2% of this cohort. Lack of regular vigorous physical activity was more frequently reported by women (68.2%, versus 56.9% of men) and ethnic minorities (73.4% of African Americans and 69.6% of Hispanics, versus 63.0% of whites/others). Almost all of these respondents had health insurance, largely through Medicare (93.4%).
Table 1. Baseline characteristics of the cohort of persons with arthritis ages 65 years and older from the 1998 Health and Retirement Study (n = 5,715)
No. (population %)
95% confidence interval
Comorbid health conditions
No chronic conditions
Vision impairment (poor vision or legally blind)
Walk several blocks
Climb several flights of stairs
Push/pull large objects
Lift/carry weight ≥10 pounds
Education <12 years
Annual family income below lower quartile ($16,800)
Net worth below lower quartile ($44,800)
Lack of regular vigorous physical activity
Ever used alcohol
Weight gain ≥10 pounds
Weight loss ≥10 pounds
The prevalence of functional limitations in daily tasks was estimated from the 5,715 arthritis cohort members. Overall, limitations in functional tasks were reported by 19.7% of the cohort, including 12.9% with at least 1 ADL limitation; 5.6% had 2 or more, and 2.9% had 3 or more. Older women (22.1%) were more likely than older men (15.5%) to experience daily task limitations, as shown in Figure 1. More than 1 in 7 women (14.8%) and almost 1 in 10 men (9.4%) with arthritis reported limitations in at least 1 basic ADL task. Severe functional limitations (≥3 ADL limitations) were reported by 3.3% of women and 2.1% of men with arthritis.
Incidence of functional decline was assessed in 4,922 subjects without severe baseline functional limitation. Over the subsequent 2 years, function declined in 13.6% of this group. Table 2 summarizes 2-year rates of functional decline by age, sex, and race/ethnicity. As expected, functional decline increased with age, almost doubling in frequency for approximately every additional decade (65–74 years 8.8%, 75–84 years 16.8%, ≥85 years 30.3%). Function declined significantly more frequently in women than in men (OR 1.4, 95% confidence interval [95% CI] 1.2–1.7), a trend that was consistent across age groups. Functional decline was significantly greater among older Hispanics (OR 1.5, 95% CI 1.1–2.0) and African Americans (OR 1.6, 95% CI 1.2–2.0) with arthritis compared with whites/others (12.9%).
Table 2. Rates of 2-year (1998–2000) functional decline, by sex, race, and age, among members of the 1998 Health and Retirement Survey arthritis cohort with no or moderate functional limitation at baseline
Sex or race, age
95% confidence interval
Male (n = 1,766)
Female (n = 3,156)
White/other (n = 4,028)
African American (n = 611)
Hispanic (n = 283)
Total (n = 4,922)
To determine the strongest predictors of functional decline, the relative effect based on adjusted OR was estimated, simultaneously controlling for comorbid health conditions, health behaviors, economic factors, and demographic differences (Table 3). Comorbid health conditions that increased the risk of functional decline included cognitive impairment (adjusted OR 2.9, 95% CI 1.7–4.8), vision impairment (adjusted OR 1.6, 95% CI 1.2–2.2), diabetes (adjusted OR 1.6, 95% CI 1.2–2.0), history of stroke (adjusted OR 1.6, 95% CI 1.1–2.3), depressive symptoms (adjusted OR 1.3, 95% CI 1.1–1.6), and physical limitation in pushing/pulling large objects (surrogate for disease severity) (adjusted OR 1.3, 95% CI 1.0–1.6). Health behaviors that were significant predictors included lack of regular vigorous physical activity (adjusted OR 1.9, 95% CI 1.5–2.4) and use of alcohol (negative predictor, i.e., predictive of less functional decline) (adjusted OR 0.8, 95% CI 0.6–0.9). Economic factors were not significant predictors of functional decline in this Medicare-aged population.
Table 3. Adjusted ORs for 2-year functional decline in the arthritis cohort (n = 4,922), by risk factor
Values are adjusted odds ratios (ORs) from a multiple logistic regression model that simultaneously controlled for comorbid conditions, health behaviors, and socioeconomic and demographic factors. 95% CI = 95% confidence interval.
Many demographic differences in functional decline (Table 2) were attenuated after accounting for health and economic factors (Table 3). Specifically, the greater frequencies of functional decline among older women and persons of African American or Hispanic ethnicity were largely explained by their greater burden of other risk factors. For example, significant and highly prevalent risk factors, including lack of regular vigorous physical activity and depressive symptoms, were reported substantially more frequently among women (lack of regular vigorous physical activity 68.3%, depressive symptoms 44.2%) than men (57.0% and 33.3%, respectively) and among ethnic minorities (72.1% and 55.3%, respectively) than whites/others (63.0% and 38.1%, respectively). Older age, however, remained a significant risk factor for functional decline that increased with each decade of age.
The strong relative effect of lack of regular vigorous physical activity on functional decline is important from a public health perspective since it was a highly prevalent risk factor (64.2%) that is modifiable. Among other health factors, only cognitive impairment, which was present in only 3% of the cohort and less amenable to intervention, had a stronger relative effect on functional decline. To better understand the potential impact of lack of regular vigorous physical activity, we explored its effect on functional decline, stratifying by baseline functional ability in the subjects with arthritis (Figure 2). Function declined less frequently in persons who engaged in regular vigorous physical activity, regardless of their baseline functional ability. Lack of regular vigorous physical activity was a particularly strong risk factor among persons with no baseline functional limitation (adjusted OR 2.3, 95% CI 1.8–3.0) or only mild baseline functional limitation (adjusted OR 3.2, 95% CI 1.3–7.6), after adjustment for demographic differences.
Since people with severe health burdens may be unable to perform regular vigorous physical activity, we investigated whether the report of specific physical limitations (walking several blocks, climbing several flights of stairs without resting, pushing or pulling large objects, lifting or carrying weights >10 pounds) altered the relationship between lack of regular vigorous physical activity and functional decline. Sensitivity analyses (data not shown) added interaction terms between physical activity and individual physical limitations; none of these interactions were significant. Further analyses explored whether regular vigorous physical activity had particular benefit for certain age, sex, or racial/ethnic groups, by adding interaction terms between physical activity and demographic characteristics to the multiple logistic regression model. None of the interactions from this analysis were significant (data not shown), indicating that lack of regular vigorous physical activity is equally detrimental in vulnerable female and minority populations.
To provide a perspective on the potential benefit of regular vigorous physical activity as a modifiable risk factor, we used standardized rates to estimate how functional decline might be affected if all persons not engaged in regular vigorous physical activity could be persuaded to become active. Overall, the 2-year rate of functional decline would be reduced by nearly one-third, from 13.6% to 9.2%, based on standardized rates with regular vigorous physical activity participation by the entire risk group. Estimated functional decline would be reduced in women from 15.0% to 10.0%, in men from 11.0% to 7.6%, in African Americans from 18.7% to 12.6%, in Hispanics from 18.0% to 12.2%, and in whites/others from 12.9% to 8.7%.
This study provides evidence of the substantial national public health burden related to functional limitations among Medicare-aged US adults with arthritis. Nearly 1 in 5 adults over age 65 years with arthritis reported limitations in functional tasks. More than 12% of this cohort reported ADL task limitations; 5.6% had 2 or more and 2.9% had 3 or more ADL limitations. This finding represents an impressively high prevalence of IADL and ADL limitations among a group of adults whose health care is largely covered by public insurance via Medicare. Among persons at risk of functional decline, >13% had a lower level of function 2 years later. Other than cognitive impairment, which was present in only 3% of this population, lack of regular vigorous physical activity was the strongest predictor across the spectrum of comorbid health conditions, health behaviors, and economic factors examined. The odds of functional decline over 2 years almost doubled among persons not engaged in regular vigorous physical activity compared with their active peers, after controlling for all other risk factors.
The prospect of developing worse levels of function is particularly daunting for older women, African Americans, and Hispanics. Approximately 1 in 7 women and almost 1 in 5 African Americans and Hispanics declined in function within 2 years. Function deteriorated more frequently among women (15.0%) compared with men (11.0%) and substantially more frequently among minorities (African Americans 18.7%, Hispanics 18.0%) compared with whites/others (12.9%). The higher rates of functional decline among older women and ethnic minorities with arthritis are largely due to greater burdens of health risk factors, such as comorbid chronic conditions and lack of regular vigorous physical activity.
To guide a public health response, we investigated the relative impact of risk factors on functional decline after controlling for comorbid health conditions, health behavior, and economic and demographic factors. In addition to lack of regular vigorous physical activity and cognitive impairment, which approximately double and triple the odds of functional decline, respectively, other significant predictors of functional decline were age, depressive symptoms, diabetes, physical limitation in pushing/pulling large objects, stroke, and vision impairment, while use of alcohol was found to be protective after controlling for all risk factors. Frail individuals are characterized by older age and chronic health conditions, and these characteristics are consistent with reports in the geriatrics literature on functional limitation risk factors (28, 29). Alcohol use has also been shown to be protective in other population-based studies (30).
The strong association between lack of regular vigorous physical activity and subsequent functional deterioration in this national arthritis cohort is particularly important from a public health point of view, since this risk factor is highly prevalent among persons with arthritis and is amenable to intervention. More than 60% of adults with arthritis do not meet the US Surgeon General's recommendations for physical activity (31). The present study showed that function declined less frequently in older adults with arthritis who engaged in regular vigorous physical activity, regardless of their baseline functional ability. To provide a perspective on the potential public health benefit of physical activity, we estimated the expected 2-year rates of functional decline if all persons in this cohort had engaged in regular vigorous physical activity. Functional decline would have been reduced as much as 32% (from 13.6% to 9.2%). These findings indicate that older persons with chronic conditions need to be encouraged to participate in physical activities, regardless of their current capabilities.
Physical activity has been considered a safe, efficacious, and widely advocated method of controlling disease consequences of arthritis (32, 33). Clinical studies of specific types of exercise programs demonstrate that physical activity interventions result in improved strength, aerobic capacity, flexibility, and physical function in patients with rheumatoid arthritis (34, 35), patients with osteoarthritis (36, 37), and sedentary older persons in general (38, 39). However, it is worth noting that in each of those clinical studies, very specific training programs were devised to produce the resultant outcomes, requiring professional resources and a high motivation level among participants. For example, strength training (all major muscle groups of the lower and upper extremities and trunk, repetitions with loads of 50–70% of maximum) was tested in patients with rheumatoid arthritis (35), while studies of patients with osteoarthritis utilized an aerobic exercise program and a resistance exercise program (36), or resistance training without an aerobic component (37). In elderly subjects without musculoskeletal diagnoses, a specific protocol of combined endurance and strength training was designed to be performed at 75–80% of maximal intensity; with the groups meeting 3 times/week for 6 months of supervised sessions (38). The impact of less formalized physical activities on functional outcomes in persons with arthritis is not known.
Large epidemiologic studies have shown lack of physical activity to be a risk factor for functional limitation, based on longitudinal findings (30, 40–44). However, these longitudinal studies are largely based on community samples (30, 40, 42, 43), rely on data from more than a decade ago (30, 40–44), and seldom controlled for health and economic factors that may partially explain their findings (30, 40–43). Population-based longitudinal studies among persons with arthritis are particularly limited (44). Results of the present study, which had a strong methodologic foundation of longitudinal data from a recent national probability sample that analytically controls for demographic, health, and economic factors, document lack of regular vigorous physical activity as a risk factor for functional decline. The focus on the experience of an arthritis cohort makes these findings relevant to the design of public health intervention and prevention programs to maintain and improve function among persons with this disease.
Despite the study's strengths, several limitations common to secondary databases may affect the present findings. Since baseline factors were assessed cross-sectionally, it is unknown which (e.g., depressive symptoms) may be consequences or causes of baseline functional problems. Second, the physical activity assessment does not provide information on the types or levels of activities in which people engaged. Also, subjects were not asked whether they were capable of physical activity. However, assessment of the impact of lack of regular vigorous physical activity relative to other risk factors controlled for baseline physical limitations, a surrogate for the severity of health burdens. Also, the risk group used for this risk factor analysis excluded subjects who initially reported severe (≥3 ADL) functional limitations, which means the findings are based on people most likely to be capable of physical activity. In this risk group, further analyses showed that lack of regular vigorous physical activity was a particularly strong risk factor for functional decline among subgroups with the highest baseline functional capability (no or mild functional limitations at baseline). Finally, some of the differences found in our multiple statistical tests could have been due to chance.
Functional limitation is a recognized factor in health care costs (5, 45). Findings from this study show that almost 20% of persons with arthritis in a cohort whose medical expenses are largely covered by Medicare have limitations in daily functional tasks. The burden of functional limitation and subsequent decline in function was greatest among older women and ethnic minorities. These findings highlight the importance of prevention programs targeted at and tailored to the needs of these vulnerable populations. The good news is that the risk factor that was the most prevalent of those examined and among the strongest predictors of functional decline, i.e., lack of regular vigorous physical activity, is amenable to prevention efforts. Motivating older persons with arthritis who are not engaged in regular physical activity to change behavior could reduce subsequent functional decline among these persons by almost one-third. Lack of regular vigorous physical activity is an important risk factor in all racial/ethnic groups and both sexes. Prevention/intervention programs should include regular physical activity, weight maintenance, and medical intervention for health needs.