A clinically relevant criterion for grip strength: relationship with falling in a sample of older adults

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1 Original research A clinically relevant criterion for grip strength: relationship with falling in a sample of older adults Michelle D Miller, Lynne C Giles, Maria Crotty, James E Harrison and Gary R Andrews Abstract (Nutr Diet 2003;61:248 52) Objective: To develop a clinically relevant criterion for assessment of grip strength in older adults. Design: Longitudinal cohort study. Subjects: 1251 persons aged 70 years who had grip strength measured as part of the Australian Longitudinal Study of Ageing (1992) and survived to a second interview 12 months later. Setting: Randomly selected sample of community-dwelling older adults residing in the Adelaide (South Australia) Statistical Division as defined by the Australian Bureau of Statistics. Main outcome measures: Participants were asked if they had any falls in the previous 12 months and the same question was repeated in the second interview. Statistical analyses: Logistic regression analyses were performed with faller status at 12 months as the dependent variable, grip strength 25th percentile as the reference category and controlling for age, gender, faller status, BMI, exercise status and chronic disease. Results: For both genders the percentage fallers was highest for those with grip strength < 25th percentile (< 28kg males, < 15.5kg females). After controlling for potential confounders, grip strength < 25th percentile independently predicted falls 12 months later (OR = 1.41, 95% CI= , P = 0.034). Conclusion: In previous studies grip strength has been shown to be positively correlated with measures of nutritional health and in this study we have shown that it is an important determinant of future falls. This knowledge could be used to help prevent falls in the elderly in the future. Further research is warranted to determine whether nutritional support interventions can (1) improve or maintain grip strength among older adults and (2) aid in the prevention of subsequent accidental falls. Key words: accidental falls, grip strength, nutrition, elderly Background Studies have shown that approximately 30% of community-dwellingpeopleovertheageof65yearshaveafall each year (1 4) and that this incidence increases to as high as 50% in those over 80 years (5). Despite the overwhelming evidence that under-nutrition is very prevalent in frail older adults who fall and break a hip (6 9), screening and interpretation of nutritional health in this vulnerable patient group has been neglected. Furthermore, decreased muscle mass, weakness and gait abnormalities are associated with under-nutrition and impaired coordination, and hence a tendency to fall is compounded by being undernourished (10). One of the issues perhaps responsible for this omission is the perceived difficulty of assessing nutritional health. It is well known that assessment of nutritional health requires a combination of indices, most of which are either expensive, require training or simply have not been shown to be clinically relevant. There is now evidence to suggest that grip strength is positively correlated with measures of nutritional health including body mass index (11), mid-upper arm circumference (11), arm muscle area (11) and lean body mass (12). Grip strength is an ideal measurement because of this relationship and also because it is inexpensive, has been shown to be reliable (13) and is easy to perform. The major limitation however in using grip strength in nutri- Flinders University Department of Rehabilitation and Aged Care, Adelaide, South Australia M. Miller, BSc, MNutrDiet, PhD Candidate M. Crotty, BMed, PhD, FAFRM, Professor and Head Faculty of Health Studies, Auckland University of Technology L. Giles, MPH, Biostatistician Research Centre for Injury Studies, Flinders University, Adelaide, South Australia J. Harrison, MBBS, MPH, FAFPHM, Director Flinders University Centre for Ageing Studies, Adelaide, South Australia G. Andrews, MBBS, FRCP, FRACP, FFRM, FRACMA, Director Correspondence: M. Miller, Flinders University Department of Rehabilitation and Aged Care, Repatriation General Hospital, Daws Road, Daw Park SA michelle.miller@rgh.sa.gov.au 248 Nutrition & Dietetics (2003) 60:4

2 tional assessment is that there is currently no agreement on clinically relevant reference values. The clinical relevance of grip strength has mainly been studied with elderly people from affluent societies and outcome variables investigated have included morbidity (13), mortality (22) and functional ability (23,24). Each of these studies has shown that low grip strength is predictive of poor outcome. However defining what constitutes a low grip strength has largely been ignored. The aim of this study was to establish gender-specific, clinically relevant reference values for grip strength that predict falls in older adults. Methods Study population The study population was a subset of a larger sample (n = 2087) of older Australians randomly selected to participate in a longitudinal study of ageing, Australian Longitudinal Study of Aging (ALSA) in Details of the ALSA study are reported elsewhere (14). Thesample of 1251 participants referred to in the present study were community dwelling, 70 years or older on the date of entrytothestudy,participatedinaninterviewandclinical assessment at baseline, and survived to participate in a second interview 12 months later. All 1251 participants were interviewed in their own homes and underwent a clinical assessment by trained observers. Ethical approval was obtained from the Clinical Investigation Committee of Flinders Medical Centre, Adelaide, South Australia. Written informed consent was obtained from each participant. Study variables For the purpose of this study, variables collected in the interview and clinical assessment were chosen for further analysis it there was some literature available supporting their association with grip strength in older adults. The variables chosen included socio-demographic and lifestyle characteristics, the presence of chronic disease and falls history. Socio-demographic and lifestyle characteristics included age (70 74; 75 79; 80 84; 85+ years), gender, body mass index (BMI: weight (kg)/height (m 2 ); < 22, 22 26, > 26 30, > 30), self-rated health (very good excellent; good; fair poor) and exercise status (self-reported engagement in exercise for recreation, sport or health fitness purposes or sedentary) (15). Grip strength [to the nearest 0.5 kg using a hand-held dynamometer (Smedlay s Dynamo Meter, TTM, Tokyo, Japan) in the dominant hand] was measured. Percentage of fallers at each grip strength reading was calculated and this suggested a non-linear relationship with faller status. Grip strength was subsequently categorised into gender-specific tertiles, quartiles, quintiles, and deciles and ROC analysis performed to determine the most suitable classification with respect to sensitivity and specificity. The best categorisation corresponded to the quartiles, and further examination showed the greatest discrimination was at the 25th percentile for both males and females. A dichotomised grip strength value was therefore used for subsequent analyses (< 25th percentile and 25th percentile). The presence of chronic disease was assessed via selfreport and included the ten most prevalent morbid conditions (any cancer, arthritis, diabetes, heart attack, heart condition, hernia, hypertension, respiratory disease, ulcers, stroke). The number of chronic conditions present were summed to give a score between 0 and 10 for each participant. This was further categorised into: 0 conditions, 1 3 conditions and 4 conditions. The outcome variable was the occurrence of falls in the year following the first interview. We used the definition of fall defined by the Kellogg International Work Group on the Prevention of Falls by the Elderly: A fall is an event which results in a person coming to rest inadvertently on the ground or other lower level and other than as a consequence of a violent blow; loss of consciousness or sudden onset of paralysis (16). Participants were asked at each interview to recall whether they had fallen on at least one occasion in the previous 12 months. If a participant reported at least one fall in the previous 12 months and the description of at least one fall was consistent with the definition described above, participants were classified as fallers. If no falls were reported in the previous 12 months participants were classified as non-fallers. Faller status was reported at both the baseline and 12 month follow-up interview. Statistical analyses All statistical analyses were conducted using the SPSS statistical package (SPSS Inc, Chicago, SPSS for Windows, Advanced Statistics, version ) and were carried out using weighted data. The sample weights were calculated to reflect the stratification of the sample by age group, gender and local government area, and were based on the probability of selection and adjusted for nonresponse. The sample weights were applied in all analyses so that the results could be generalised to the older population resident in Adelaide at the time the study was conducted. Chi square tests of association for categorical variables and independent samples t-tests for continuous variables were used to test for differences between fallers and non-fallers. Multiple logistic regression was used to examine the effect of low grip strength on subsequent falls (dependent variable), adjusting for the socio-demographic, lifestyle and morbidity characteristics of the participants already described. Odds ratios (ORs) and 95% confidence intervals (CI) are reported and statistical significance was set at P < 0.05 throughout. Results The mean age (SD) of the 1251 participants at entry into the study was 76.1 ± 5.0 years, and 44% were female. At the time of the first interview, 346 (28%) of the sample reported that they had fallen at least once in the previous 12 months. Over the 12 months of follow-up, 280 (22%) of the 1251 participants reported that they had experienced at least one fall. Differences in study variables between fallers and non-fallers at baseline are shown in Table 1. The results show fallers were older, more likely to be female, and more likely to be sedentary in comparison to non-fallers. At baseline, fallers had more chronic conditions than non-fallers. There was no difference in BMI identified between fallers and non-fallers at baseline. Nutrition & Dietetics (2003) 60:4 249

3 Table 1. Baseline data for the 1251 participants (680 males) of the Australian Longitudinal Study of Ageing by faller status Nonfallers Fallers P (a) Participant characteristics (n = 905) (n = 346) Age (years) Mean ±SD 75.8 ± ± 5.3 <0.001 Gender (%) Female <0.001 Chronic conditions (%) Self-rated health (%) Very good Excellent Good Fair Poor Exercise status (%) Sedentary BMI (kg/m 2 ) Mean ± SD 26.0 ± ± <22(%) (%) > (%) >30(%) Grip strength (kg) Mean ± SD 26.3 ± ± 8.5 <0.001 (a) Chi square tests of association for categorical variables and independent samples t-tests for continuous variables were used to test differences between fallers and non-fallers. (a) % fallers 12 mth follow-up < 28 < 15.5 Grip strength (kg) male female Gripstrengthdichotomisedat<28kgmales,<15.5kgfemales, equivalent to < 25th percentile. Statistical significance between fallers and non-fallers: P< Figure 1. Percentage fallers at 12 months follow-up classified according to grip strength for 1251 participants in the Australian Longitudinal Study of Ageing (a) The mean grip strength was 32.4 (± 7.0) kg and 19.0 (± 5.3) kg for males and females respectively. Grip strength was subsequently classified based on quartiles for the two genders. As shown in Figure 1, the percentage of fallers at 12 months follow-up was markedly higher for participants in the lowest quartile of grip strength (< 28 kg males, < 15.5 kg females; P < 0.001). Table 2 shows the results of the final multiple logistic regression model using faller status at the second interview as the dependent variable. The results show that after controlling for variables including age, gender, exercise, chronic conditions, BMI and previous faller status, a grip strength below the 25th percentile for both males and females predicts faller status after one year of follow-up. The Nagelkerke R 2 values were 6.8% excluding grip strength and 7.3% including grip strength in the model. The odds ratio and 95% confidence interval associated with grip strength changed negligibly when BMI, chronic conditions and exercise status were excluded. Table 2. Multivariate logistic regression model (OR, 95% CI) using faller status at one year follow-up as the dependent variable for 1251 participants of the Australian Longitudinal Study of Ageing (a) Study variables OR 95% CI P Age category (years) Gender Male 1.00 Female Faller status at baseline Non-faller 1.00 Faller <0.001 BMI (kg/m 2 ) < > > No. chronic conditions Exercise status Regular exercise 1.00 Sedentary Grip strength (kg) (a) 25th percentile 1.00 < 25th percentile th percentile: 28 kg males, 15.5 kg females. 250 Nutrition & Dietetics (2003) 60:4

4 Discussion We measured the prevalence of falls among older community-living adults and found that the prevalence was markedly higher for those with low grip strength. We also found that low grip strength has potential as a clinical indicator of falls risk, as in our sample we were able to show that even after accounting for potential confounders, low grip strength independently predicted falls 12 months later. The significance of the potential confounders may be expected but what is new is that even after adjusting for these, nutrition (as measured by grip strength) remains strongly predictive of falls. Hand-grip dynamometry is a measure of muscle function. This protein content and the evidence that suggests hand-grip strength is positively associated with nutritional status is increasing both in developed (17) and developing countries (11). There is also evidence to suggest that poor nutritional health (both overweight and underweight) has implications in terms of falls risk (18 20). Several assessment techniques are used in the diagnosis of poor nutritional health, however none of these alone are considered adequate. In contrast, nutrition screening tools which are commonly used to identify those patients who are more likely to be at risk often refer to a single variable. An example of this is the World Health Organization recommendation that mid-upper arm circumference is a useful tool to identify those older adults who might benefit from nutrition intervention (21). The measurement of grip strength is rapid, reproducible, does not require extensive training and is inexpensive. These are all important considerations when making decisions about which nutrition screening tool or nutritional assessment techniques should be used. When these measures are shown to have clinical relevance, this makes the measurement significantly more robust. The clinical relevance of grip strength has largely been studied with elderly people from affluent societies and outcome variables investigated have included morbidity (13), mortality (22) and functional ability (23,24). Each of these studies has shown that low grip strength is predictive of poor outcome. More relevant to our study are the results published in 1989 by Wickham et al. (25) which reported on grip strength and risk of falls in elderly people. The authors of this study reported on results obtained from a national survey in Britain in which 983 elderly people were asked about their falls history. These data were analysed by multiple logistic regression, after controlling for mobility, non-phenothiazine tranquillisers, number of cohabitants, recent weight loss and physical disability. The authors concluded that those who had fallen one or more times had reduced grip strength. Our study has confirmed these results in an Australian sample of older adults and further has been able to look at the predictive relationship of low grip strength and falls in a longitudinal analysis. The results of this study must be interpreted with caution if the intention is to apply the results to other populations. The study protocol was extensive and this may have favoured refusal to participate and loss to follow up among members of the study population who were in particularly poor health. The use of grip strength as a nutritional marker has also been questioned with some research suggesting that perhaps grip strength is more an indicator of general debility or frailty (26 27). In this study we found that grip strength was an independent predictor of falling, even after controlling for the presence of chronic diseases. In principle, analysis after stratification according to levels of BMI might enable overt exploration of possible interactions of BMI, grip strength and falling. We did consider interactions between BMI and grip strength and found no evidence for an interaction between the two variables. The relationship of grip strength and nutritional health is becoming increasingly recognised although remains underutilised as a nutritional assessment tool, perhaps due to some literature suggesting it is merely a measure of frailty. Although analysis of the relationship between grip strength and nutritional health was beyond the scope of this study, we suggest that low grip strength is an important risk factor for falls among older adults and have provided clinically relevant reference values for use in clinical practice. Further research is warranted to determine whether nutritional support interventions can improve or maintain grip strength among older adults and aid in the prevention of subsequent accidental falls. Furthermore it would be interesting to determine whether grip strength can predict alternative clinical outcomes such as mobility and hospital admissions. Acknowledgments The data for this study were obtained from the Australian Longitudinal Study of Ageing data set held by the Centre for Ageing Studies, Flinders University of South Australia. This study was supported in part by the South Australian Health Commission, the Australian Rotary Health Research Fund and by a grant from the US National Institute of Health (Grant No. AG ). References 1. Prudham D, Evans JG. Factors associated with falls in the elderly: a community study. Age Ageing 1981;10: Campbell AJ, Reinken J, Allan BC, Martinez GS. Falls in old age: a study of frequency and related clinical factors. 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