Original Article
A cohort study found good respiratory, sensory and motor functions decreased mortality risk in older people

https://doi.org/10.1016/j.jclinepi.2004.08.015Get rights and content

Abstract

Background and Objective

The main aims of this study were to evaluate the separate and joint effects of respiratory, sensory, and psychomotor function, muscle strength, and mobility in predicting mortality in older men and women, and to find a way to control multicollinearity in a multivariate Cox regression model.

Methods

Mortality was followed for 10 years (1990–2000) in an entire cohort of 75-year-old residents of the city of Jyväskylä, Finland (born in 1914; N = 388). Cox regression models and principal component estimation were employed to study the association between the covariates and mortality.

Results

The study indicated that, after adjustment for fatal diseases and cognitive capacity, vital capacity, tapping rate, muscle strength, and walking speed predict mortality in elderly men and women to a similar extent. The hazard ratio for mortality for those in the lowest tertile of the principal component representing all the significant physiological functions was from three to four times higher than for those in the highest tertile.

Conclusion

Our results suggest that a poor level in any of the measured functions has a similar impact on the risk for mortality, which is further increased by combining the different results. No single, dominant predictor of mortality emerged.

Introduction

Survival is a central element in the epidemiology of old age. Differences between individuals in the length of life challenge the research community to attain a better understanding of the influences and mechanisms of risk factors on mortality, because these factors change with increasing age and thus differ from those same factors in younger age groups. Furthermore, mortality risk factors in individuals in the higher age groups are often multiple and interact [1].

Beyond the effects of age, sex, and socioeconomic status, the risk of mortality in elderly people has been found to be affected by a wide range of factors, including both self-rated and objectively measured functional capacity and health [2], [3], [4]. One approach to the study of functional capacity in elderly people is to measure their level of self-reported ability in carrying out the activities of daily living; difficulties in performing these tasks have found to be associated with increased mortality [5], [6]. Recently, interest has been shown in the use of performance-based measures of individual functioning, such as muscle strength or mobility, as possible risk factors for health outcomes in elderly people. It has been confirmed in a number of studies that (for example) good muscle strength [7], [8], [9], [10], good physical mobility [11], [12], and high pulmonary function [13], [14] predict better survival in older populations. We have not been able to locate any studies focusing on other physiological functions, such as tapping rate or sense of vibration, in relation to mortality in old age.

Several recent studies have tried to identify distinctive features to define a frailty phenotype [15], [16], [17]. Frailty is currently conceptualized as a pathologic condition that results in a typical constellation of signs and symptoms, impending decline in physical function, and high risk of death [15]. Although there is no consensus on frailty syndrome, it usually includes weakness and slowness [18].

Despite the large number of studies on functional capacity and mortality in elderly people, measures representing different domains of physical function and health have rarely been included in the same study. Despite significant advances in our understanding of mortality risk in elderly people, many unanswered questions remain. For instance, the relative role and impact of different risk factors continues to be unclear; there are very few comprehensive studies in which several physiological functions have been investigated at the same time. Most previous studies on mortality in elderly people have had relatively short follow-up times, and the age of the subjects has varied widely. Furthermore, when different domains of the same phenomenon, such as functional capacity, are studied simultaneously, the variables tend to correlate with each other, thus violating the assumptions and invalidating the results of multivariate regression models. No solutions to deal with this problem in Cox regression models have as yet been found.

The aims of the present study were to (a) identify and evaluate how respiratory, sensory, and motor function predict mortality separately; (b) study possible differences between the sexes in the risk factors for mortality; (c) study how these several functions jointly predict mortality; and (d) find a way to control for multicollinearity in Cox regression models.

Section snippets

Study population

This study forms a part of the Evergreen Project, the purpose of which was to profile and follow up the health and functional capacity of elderly residents in the city of Jyväskylä, central Finland, and identify the factors that predict changes in functional capacity and health, including mortality. The design of the project is described in detail elsewhere [19]. The eligible subjects consisted of all the 75-year-old residents (born in 1914) of Jyväskylä who were alive at the beginning of year

Total mortality

In March 2000, 45 of 104 men (43.3%) and 111 of 191 (58.1%) women had survived the 10-year follow up. In the Cox regression model, the hazard ratio (HR) for men to die was 1.48 (95% CI = 1.05–2.07) relative to the women. The difference between the sexes in overall mortality supported the assumption that separate models for men and women would be required.

Table 1 presents the descriptive statistics and the baseline measurements chosen in the final models by vital status and sex.

Separate models for continuous variables

Table 2 shows the

Discussion

The association between the various measures of physiological function and 10-year all-cause mortality among subjects aged 75 years at the baseline was investigated in an entire cohort of 295 subjects. The results showed that those who had poor results in these measurements (with the exception of vibration threshold in men) had more than two to three times higher risk for mortality than those with good results at the baseline. Combining the significant risk factors into an index and dividing it

Acknowledgments

The Evergreen Project has been supported financially by the Academy of Finland, the Social Insurance Institution, the Ministry of Education, the Ministry of Social Affairs and Health, the City of Jyväskylä, the Association of Finnish Lions Clubs, and the Scandinavian Red Feather Project. The authors are participants in the Burden of Disease in Old Age (BURDIS) network, which is a project within Key Action 6—The Ageing Population and Their Disabilities of the European Union's Quality of Life and

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