Hand grip strength and incident ADL disability in elderly Mexican Americans over a seven-year period

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1 Aging Clinical and Experimental Research Hand grip strength and incident ADL disability in elderly Mexican Americans over a seven-year period Soham Al Snih 1,2,3, Kyriakos S. Markides 2,3, Kenneth J. Ottenbacher 2,3,4, and Mukaila A. Raji 1,2 1 Department of Internal Medicine, 2 Sealy Center on Aging, 3 Department of Preventive Medicine and Community Health, 4 Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, TX, USA ABSTRACT. Background and aims: Little is known about muscle strength as a predictor of disability among older Mexican Americans. The aim of this study was to examine the association between hand grip strength and 7-year incidence of ADL disability in older Mexican American men and women. Methods: A 7-year prospective cohort study of 2493 non-institutionalized Mexican American men and women aged 65 or older residing in five south-western states. Maximal hand grip strength test, body mass index, cognitive function, activities of daily living, self-reports of medical conditions (arthritis, diabetes, heart attack, stroke, cancer, hip fracture), and depressive symptoms were obtained. Results: In a Cox proportional regression analysis, there was a linear relationship between hand grip strength at baseline and risk of incident ADL disability over a 7-year follow-up. Among non-disabled men at baseline, the hazard ratio of any new ADL limitation was 1.90 (95% CI ) for those in the lowest quartile, when compared with men in the highest hand grip strength quartile, after controlling for age, marital status, medical conditions, high depressive symptoms, MMSE score, and BMI at baseline. Among non-disabled women at baseline, the hazard ratio of any new ADL limitation was 2.28 (95% CI ) for those in the lowest quartile, when compared with women in the highest hand grip strength quartile. Conclusions: Hand grip strength is an independent predictor of ADL disability among older Mexican American men and women. The hand grip strength test is an easy, reliable, valid, inexpensive method of screening to identify older adults at risk of disability. (Aging Clin Exp Res 2004; 16: ) 2004, Editrice Kurtis INTRODUCTION Progressive accumulation of functional disability is a major cause of poor quality of life and nursing-home place- ment in the elderly. Past studies have shown that decline in muscle strength was associated with increased risk of disability in activities of daily living (ADL) and loss of independence in older adults (1-4). The Honolulu Heart Program (3) reported that, among initially non-disabled 45-to 68-year old Japanese-American men, the odds of reporting self-care disability at the 25-year follow-up were more than twice as high in subjects with the lowest hand grip strength categories at baseline, compared with those in the highest category. Similarly, Giampaoli et al. (1), using data from the Finland, Italy, Netherlands Elderly (FINE) study, in a group of 140 non-disabled older community-dwelling men, reported that decreased hand grip strength at baseline was a significant predictor of ADL disability 4 years later for those aged 77 years and older, after controlling for relevant confounders. A similar relationship between poor hand grip strength and increased disability has also been described in older women. A study of 1002 disabled black and white women aged 65 years and older found a significant cross-sectional relationship between poor muscle strength, measured by hand grip and knee extension forces, and increased risk of motor disabilities (3). Given the need to identify potentially modifiable factors for independent living in the Hispanic population and the lack of longitudinal research on muscle function in this ethnic group, we examined whether muscle strength (measured by hand grip strength) was associated with incident disability over a 7-year period in a large probability sample of older Mexican American men and women. METHODS Sample Data used were taken from the Hispanic Established Populations for the Epidemiological Study of the Elderly (EPESE), a longitudinal study of Mexican Americans aged Key words: ADL, aging, disability, hand grip strength, Mexican Americans. Correspondence: S. Al Snih, MD, Sealy Center on Aging. The University of Texas Medical Branch, Galveston, TX , USA. soalsnih@utmb.edu Received December 12, 2003; accepted in revised form April 3, Aging Clin Exp Res, Vol. 16, No

2 S. Al Snih, K.S. Markides, K.J. Ottenbacher, et al. 65 and older, residing in Texas, New Mexico, Colorado, Arizona and California. The Hispanic EPESE was modeled after previous EPESE conducted in New Haven, East Boston, rural Iowa, and North Carolina (5). Subjects were selected by area probability sampling procedures which involved selection of counties, census tracts, and households within selected census tracts. Door-to-door screening yielded in-home interviews with 3050 subjects during the fall of 1993 and spring of The sample and its characteristics have been described elsewhere (6). The response rate was 83 percent at baseline ( ), which was comparable with the other EPESE studies. Of the 3050 subjects, 2873 were interviewed in person and 177 (5.8%) by proxy. Interviews were conducted in Spanish or English, depending on the respondent s preference. The present study uses baseline data ( ) and data obtained from a 2-year follow-up ( ), a 5-year follow-up ( ) and a 7-year follow-up assessment ( ). The sample at baseline consisted of 2493 subjects with complete data on measures of hand grip strength and other relevant variables. Among those without complete data (N=557), 395 had no measured hand grip strength and 133 had missing covariate data. Of those without hand grip strength measures, 177 were interviewed via proxy; 35 had an assisted proxy interview; 69 had arm surgery; 66 refused to perform the task; 48 felt the procedure was unsafe; and 29 had missing values on the hand grip strength measure. These subjects were likely to be older (age 76.6 vs 72.6), to have had a heart attack (16.6 vs 10.2%), hip fracture (6.4 vs 3.1%), stroke (13.0 vs 5.8%), arthritis (47.2 vs 38.8%), cancer (8.9 vs 5.1%), high depressive symptoms (38.7 vs 22.8%), and be ADL disabled (41.0 vs 9.8%). Among those with complete data, 2289 subjects reported no limitation in activities of daily living (walking across a small room, bathing, grooming, dressing, eating, transferring from a bed to a chair, using the toilet) at baseline. At the 7-year follow-up, 297 subjects refused to be re-interviewed or were lost to follow-up, and 570 subjects had died, as confirmed through the National Death Index (NDI) and reports from relatives. Measures Grip strength test Using a hand-held dynamometer (Jaymar Hydraulic Dynamo-meter model #5030J1- J.A. Corp), hand grip strength was measured in kilograms (kg) at baseline ( ). In a sitting position with elbow resting on the table and palm facing up, the dynamometer was placed in the subject s dominant hand. Grip size was adjusted so that the subject felt comfortable while squeezing the grip. The subjects were instructed and verbally encouraged to squeeze the hand grip as hard as they could. The test was administered by a trained interviewer, and two trials were performed, and the highest of the two hand grip scores was used for scoring purposes. Scores were divided into approximate quartiles, separately, for men and women. For men, grip strength of <22.00 kg received a score of 1; kg, 2; kg, 3; and kg, 4. For women, grip strength of <14.00 kg received a score of 1; kg, 2; kg, 3; and kg, 4. We also analyzed the hand grip strength score as a continuous variable. The hand-held dynamometer has been shown to be a reliable and valid instrument in older persons (7-10). Functional disability Functional disability was assessed by seven items from a modified version of the Katz Activities of Daily Living (ADL) scale. ADLs include walking across a small room, bathing, grooming, dressing, eating, transferring from a bed to a chair, and using the toilet. The original version of the Katz ADLs scale (11) was modified by removing continence, because incontinence may be present in individuals who otherwise display no disability; and by adding grooming and ability to walk across a small room (12). Test-retest reliability over the short-term has been found to be high (95 to 98%) (13) and the seven-item scale in this study has a high internal reliability (alpha 0.90). Subjects were asked if they could perform the ADL activity without help, if they needed help, or if they were unable to perform it. For analysis, ADL disability was dichotomized, as no help needed versus needing help with or unable to perform one or more of the seven ADL activities. Covariates Baseline sociodemographic variables included age, gender, marital status, and years of education. The presence of various medical conditions was assessed by a series of questions asking subjects if they had ever been told by a doctor that they had arthritis, diabetes, heart attack, stroke, cancer or hip fracture. Body Mass Index (BMI) was computed as weight in kilograms divided by height in meters squared. Anthropometric measurements were collected in the home using the methods and instructions similar to those employed in other EPESE studies. Height was measured using a tape placed against the wall, and weight using a Metro 9800 measuring scale. Participants with BMIs of 30 or over were considered obese (14). Depressive symptomatology was measured according to the Center for Epidemiologic Studies Depression Scale (CES-D) (15). This scale consists of 20 items asking how often specific symptoms were experienced during the past week; responses were scored on a 4-point scale (ranging from rarely or none of the time, to most or all of the time: 0,1,2,3) with potential total scores ranging from Alpha reliability with these data was As is common in the literature, we considered persons scor- 482 Aging Clin Exp Res, Vol. 16, No. 6

3 Hand grip strength and disability ing 16 or over to experience severe depressive symptomatology (16). Cognitive function was assessed with the Mini Mental State Examination (MMSE) (17, 18). Scores have a potential range of 0 to 30, lower scores indicating poorer cognitive ability. Analysis Cox proportional hazard regressions were used to calculate the hazard ratio of incidence of any ADL disability at 2-, 5- or 7-year follow-ups, as a function of quartiles of hand grip strength, controlling for selected medical conditions and sociodemographic variables at baseline separately for men and women. These analyses were restricted to those who were non-adl disabled at baseline. Those subjects who died or were lost to follow-up were censored at the date of the last follow-up. We also analyzed the hand grip strength score as a continuous variable to investigate if there was a gradient of risk at onset of disability. Because of gender differences in muscle strength, the analysis was conducted separately for men and women (19-21). Interaction effects were measured between hand grip strength and age, medical conditions, high depressive symptoms, MMSE score, and obesity. All analyses were performed using the SAS System for Windows, Version 8 (SAS Institute, Cary, N.C.). RESULTS Table 1 presents baseline characteristics of the sample by gender. The average age was 72 years, and 57.9% of the sample was female. Over half the subjects were currently married, and the average number of years of formal education was 5. Arthritis, hypertension, and diabetes were the most common medical conditions in both men and women. Hand grip strength was lower in women than Table 1 - Descriptive characteristics of sample at baseline ( ) by gender (N=2493). Predictor variables Men Women N=1050 N=1443 Age, mean ±SD 72.5± ±6.2 Education (years)** 5.0± ±3.8 Marital status (%Married)* 794 (75.6) 620 (43.0) Hand grip strength, mean ±SD* 28.7± ±6.2 Heart attack*** (%) 121 (11.5) 126 (8.7) Stroke (%) 66 (6.3) 68 (4.7) Arthritis* (%) 291 (27.6) 686 (47.5) Obesity (BMI 30 kg/m 2 )* (%) 245 (23.3) 517 (35.8) Hip fracture (%) 23 (2.2) 49 (3.4) Cancer (%) 54 (5.1) 75 (5.2) Depressive symptoms (CES-D 16)* (%) 159 (15.1) 391 (27.1) Diabetes (%) 294 (28.0) 385 (26.7) MMSE, mean ±SD 25.2± ±3.9 Any ADL limitation*** (%) 71 (6.8) 133 (9.2) *p-value <0.0001; **p-value <0.001; ***p-value <0.01. SD=Standard deviation, BMI=Body Mass Index, CES-D=Center for Epidemiologic Studies Depression Scale, MMSE=Mini Mental State Examination. in men. Women were more ADL disabled than men, were more obese, and had more depressive symptoms. Figure 1 presents the status of the sample at the 7-year follow-up among those subjects who were ADL independent at baseline. Of the 979 men independent at baseline in ADL activities, 387 (39.5%) remained so, 170 (17.4%) had become ADL dependent, 300 (30.6%) had died, and 122 (12.5%) were lost to follow-up or refused to be re-interviewed. Of the 1310 women independent in ADL activities at baseline, 538 (41.1%) remained so, Total sample N=2493 Men non-adl disabled at baseline N=979 Women non-adl disabled at baseline N=1310 Remained non-adl disabled N=387 (39.5%) Became ADL disabled N=170 (17.4%) Deaths N=300 (30.6%) Lost to follow-up/ refused N=122 (12.5%) Remained non-adl disabled N=538 (41.1%) Became ADL disabled N=327 (25.0%) Deaths N=270 (20.6%) Lost to follow-up/ refused N=175 (13.3%) Figure 1 - Status of sample at 7-year follow-up among non-adl disabled older Mexican American men and women at baseline. Aging Clin Exp Res, Vol. 16, No

4 S. Al Snih, K.S. Markides, K.J. Ottenbacher, et al. Table 2 - Incidence of ADL limitation and total number of deaths at 7-year follow-up by hand grip strength quartiles for men and women. Hand grip strength No ADL limitation ADL limitation at ADL limitation at ADL limitation at Total of deaths at quartiles at baseline 2-year follow-up 5-year follow-up 7-year follow-up 7-year follow-up N N (%) N (%) N (%) N (%) Men (N=979) <22.01 Kg (7.4) 16 (7.0) 14 (6.1) 94 (40.9) Kg (5.3) 32 (12.2) 16 (6.1) 94 (35.7) Kg (4.6) 18 (7.6) 7 (2.9) 63 (26.4) Kg (1.2) 12 (4.8) 10 (4.0) 49 (16.3) Women (N=1310) <14.00 Kg (13.0) 33 (11.6) 29 (10.2) 90 (31.6) Kg (9.5) 42 (13.2) 21 (6.6) 70 (22.1) Kg (4.9) 34 (9.3) 34 (9.3) 68 (18.5) Kg (3.2) 16 (4.7) 22 (6.5) 42 (12.3) 327 (25.0%) had become ADL dependent, 270 (20.6%) had died, and 175 (13.3%) were lost to follow-up or refused to be re-interviewed. Table 2 shows the incidence of ADL disability at each follow-up and the total number of deaths, by hand grip strength quartiles for men and women. Among the men in the two lowest hand grip strength quartiles, 44.1% reported no ADL limitation over time compared with 25.1% of men in the two highest quartiles. Among the women in the two lowest hand grip strength quartiles, 64.1% reported no ADL limitation over time compared with 37.6% of women in the two highest quartiles. Of the 300 men and 270 women who had died, 40.9 and 31.6% were in the lowest hand grip strength quartile, respectively. Table 3 presents the results of Cox proportional hazard analysis of the 7-year incidence of any ADL limitation as a function of grip strength quartile, controlling for age, marital status, medical conditions, high depressive symptoms, MMSE score, and BMI for men and women. Among non-disabled men at baseline, the hazard ratio of any new ADL limitation was 1.90 (95% CI ) for those in the first quartile, 1.83 (95% CI ) for those in the second, and 1.25 (95% CI ) for those in the third, when compared with men in the fourth quartile, controlling for age, marital status, medical conditions, high depressive symptoms, MMSE score, and BMI at baseline. Similar results were also found when hand grip strength was used as a continuous variable. Among non-disabled men at baseline, each 1-kg increase in hand grip strength was associated with a 3% decrease risk of any ADL limitation, after controlling for the variables listed in Table 3 (HR=0.97; 95% CI ). Older age (HR=1.07; 95% CI ) and diabetes (HR=1.06; 95% CI ) were also significant predictors of ADL disability in men. Table 3 - Hazard ratio analysis predicting 7-year incidence of any ADL limitation from hand grip strength among non-disabled older Mexican American men and women. Predictor variables Men Women HR 95% CI HR 95% CI N=979 N=1310 Age (years) 1.07 ( ) 1.06 ( ) Education (years) 1.01 ( ) 0.99 ( ) Marital status (married) 0.92 ( ) 0.91 ( ) Hand grip strength quartiles 1 st 1.90 ( ) 2.28 ( ) 2 nd 1.83 ( ) 1.72 ( ) 3 rd 1.25 ( ) 1.41 ( ) 4 th Heart attack 0.98 ( ) 1.35 ( ) Stroke 1.48 ( ) 0.99 ( ) Arthritis 1.18 ( ) 1.24 ( ) Obesity (BMI 30 kg/m 2 ) 1.12 ( ) 1.21 ( ) Hip fracture 2.20 ( ) 1.81 ( ) Cancer 0.67 ( ) 1.02 ( ) Depressive symptoms (CES-D 16) 1.23 ( ) 1.12 ( ) Diabetes 1.86 ( ) 1.70 ( ) MMSE score (each point) 0.97 ( ) 0.97 ( ) BMI=Body Mass Index, CES-D=Center for Epidemiologic Studies Depression Scale, MMSE=Mini Mental State Examination. Among non-disabled women at baseline, the hazard ratio of any new ADL limitation was 2.28 (95% CI ) for those in the first quartile, 1.72 (95% CI ) for those in the second, and 1.41 (95% CI ) for those in the third, when compared with women in the fourth quartile, controlling for the same variables as for men. Similar results were also found when hand grip strength was used as a continuous variable. Among non-disabled women at baseline, each 484 Aging Clin Exp Res, Vol. 16, No. 6

5 Hand grip strength and disability 1-kg increase in hand grip strength was associated with a 5% decrease risk of any ADL limitation, after controlling for the variables listed in Table 3 (HR=0.95; 95% CI ). Older age (HR=1.06; 95% CI ), arthritis (HR=1.24; 95% CI ), hip fracture (HR=1.81; 95% CI ) and diabetes (HR=1.70; 95% CI ) were also significant predictors of ADL disability in women. No interaction effects were found for hand grip strength and age, medical conditions, high depressive symptoms, MMSE score, and obesity in predicting ADL disability. DISCUSSION This study examined the effects of baseline hand grip strength on subsequent ADL function among community-dwelling Mexican American men and women aged 65 and older. There was a significant relationship between lower hand grip strength quartile and increased risk of any ADL limitations over a 7-year follow-up. Men and women in the lowest hand grip strength quartile were twice as likely to report an ADL limitation over time compared with men and women in the highest hand grip strength quartile at baseline. These results are consistent with earlier findings on the association between hand grip strength and risk of disability (1-4). Rantanen et al. showed that lower hand grip strength measured at baseline among Japanese men aged 45 to 68 years living in Hawaii was associated with a higher risk of slower walking speed, decreased ability to rise from a chair, and reporting difficulty with selfcare activities, compared with those with higher grip strength over a 25-year period, adjusting for relevant confounders (3, 4). Our study extends prior studies by showing a stepwise decrease in the risk of future disability with higher scores on hand grip strength measured at baseline, so that each 1-kg increase in hand grip strength is associated with a 3-5% decrease in the risk of any ADL disability over a 7-year follow-up in our cohort of initially non-disabled subjects. Thus, an inexpensive and easily administered measure of muscle strength (hand dynamometer) may be used as a prognosticator of future ability for self-care capacity and independent living. There are potential explanations on how poor muscle strength, as measured by hand grip strength, may influence subsequent ability to walk across a small room, bath, and transfer from a bed to a chair, among others. Prior studies have reported an association between progressive resistance strength training in the elderly and subsequent improvement in gait speed, stair climbing activity and overall physical function (22-24). Binder et al. (22) found that, after 9 months of combined flexibility, balance, and resistance exercise-training in sedentary community-dwelling subjects aged 78 and older, there was a significant improvement among the exercise group compared with the control group in peak oxygen uptake (meaning less fatigue during ADL activities), in measured ability to stand up 5 times from a 16-inch chair, and in self-reported ability to perform ADLs, after adjustments for relevant confounders. In contrast, findings from a recent review of 66 randomized trials of progressive resistance training in the elderly found no evidence for the beneficial effect of resistance training on objectively measured markers of physical disability or health-related quality of life, despite an improvement in measures of muscle strength and functional limitations such as gait speed (23). Clearly, more studies are needed to unravel the role of muscle strength and muscle function in the disablement-enablement process. Another plausible explanation is that unmeasured factors (such as poor nutrition, muscular dystrophy and sub-clinical stroke) may be causing decline in both muscle strength and ADL performance. In this scenario, poor muscle strength is captured, or verified; much earlier by measuring grip strength during a period when subjects report no disability. However, over a 7-year follow-up period, with progressive decline in muscle strength as well as the persistence of any unrecognized condition, deficits in ADL performance accumulate, leading to physical disability and loss of independence. Indeed, some studies have reported the beneficial effect of nutritional supplements, in addition to exercise training, on physical performance in the elderly (25, 26). We have no direct evidence that incident ADL disability at follow-up is due to poor nutrition or any specific medical illness known to cause decline in muscle strength and ADL ability. This study has some limitations. The first is generalizability to other older populations. Older Mexican Americans are more disabled than older Non-Hispanic Whites, and have differing prevalence rates for some diseases than do other ethnic groups (6). Second, the assessment of ADL was by self-report. However, several studies have demonstrated good fits between self-reported data and direct observations of ADL performance (27). Third, the medical conditions were also by self-report. Despite these limitations, our study has several strengths, including its large sample of men and women living in the community, its prospective design, and its use of hand grip strength to measure muscle function. The choice of hand grip strength as a measure of muscle strength was based on several studies (3, 8, 28-30) in which it was used as an overall measure of muscle strength, and because it is reliable, valid, and easy to administer. In conclusion, our study showed that poor upper extremity muscle strength, measured by hand grip strength, is associated with increased risk of incident ADL disability over a 7-year period in a population-based sample of older Mexican Americans living in the community. The association between lower baseline grip strength and inci- Aging Clin Exp Res, Vol. 16, No

6 S. Al Snih, K.S. Markides, K.J. Ottenbacher, et al. dent disability in ADL over seven years suggests that older Mexican Americans with low upper body muscle strength may benefit from interventions targeted at enhancing muscle strength and physical functioning. One approach to slowing age-related sarcopenia in this population is a trial of culturally appropriate interventions, to promote increased physical activities and the adoption of diets known to enhance muscle strength, particularly among those in the lower quartiles of grip strength measures. Using a simple and easily administered test of muscle strength is one way of obtaining useful information for the development of public health programs to reduce the risk of future disability among elderly Mexican Americans, a rapidly growing segment of the older population in the United States. ACKNOWLEDGEMENTS This study was supported by grants AG10939 and AG17231 from the National Institute on Aging, USA. 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