Incidence and risk factors of disability in the elderly: The Rotterdam Study

Abstract

Background.

This study analyzed the incidence of disability and its risk factors in multiple dimensions in community-dwelling women and men of older age, between 1990 and 1999, in Rotterdam, The Netherlands.

Methods.

For this community-based prospective longitudinal study, data were obtained from the Rotterdam Study that comprised a cohort of 7983 elderly who are 55 and over. The study sample for incident disability consisted of 4258 subjects who were disability free at baseline and had complete outcome data at follow-up, 6 years later. Sociodemographic factors, lifestyle variables, health conditions and disability status were assessed at baseline and follow-up. Disability was defined as a Disability Index (DI) ≥ 0.50 according to the Health Assessment Questionnaire.

Results.

Multivariate analyses, performed separately due to gender differences, revealed that age, self-rated health, overweight, depression, joint complaints, medication use were predictors of disability for both men and women. Stroke, falling and presence of comorbidities predicted disability in men only while having a partner, poor cognitive functioning, osteoarthritis and morning stiffness only predicted disability in women.

Conclusion.

Identified risk factors in this study are to some extent modifiable, enabling interventive strategies, reckoning with gender differences in risk profile, in order to prevent disability.

Introduction

The increase of life expectancy due to socioeconomic and medical progress in the 20th century has yielded a population of elderly people that is growing in size and proportion. At present many Western populations are aging. In The Netherlands for instance, people of age 65 and older constitute 13% of the total population, ranging from 6% to 27% in different regions. As by 2010 the generation of the ‘after war baby boom’–referring to the increased birth-rate after the end of the Second World War–will pass the age of 65, this proportion will increase further. It is estimated that by the year 2040 23% of the Dutch population will be 65 years or older. This proportion is then expected to remain stable and reach a new equilibrium (Tas and Alders, 2001).

Although the prospect of a longer life may rejoice many of us, the absolute and proportional increase of the older population entails troubling medical and economical consequences for the individual and society. In general the risk of disability for Activities of Daily Life (ADL), comprising bathing, dressing, toileting, transfer and feeding, increases with increasing age (Jagger et al., 2001). In most cases disability is a chronic condition raising health care costs for society and reducing the quality of life of elder individuals. Furthermore, physically disabled elderly have a higher risk of dying or being institutionalized (Mor et al., 1994).

Incidence rates in the literature for ADL disability with different lengths of follow-up and within different age groups range from 5.6% to 47% (Jagger et al., 2001, Woo et al., 1998, Sauvel et al., 1994, Seeman et al., 1996, Laukkanen et al., 1997). Kivela and colleagues report an incidence rate of 14% over 5 years while Penninx and colleagues report 25% over 6 years (Kivela and Pahkala, 2001, Penninx et al., 1999). Furthermore, several studies show different levels of statistical significance for the association of certain determinants of disability among which gender, body mass index, cognitive functioning and stroke (Woo et al., 1998, Seeman et al., 1996, Colvez et al., 1987, Laukkanen et al., 1997, Bruce et al., 1994, Penninx et al., 1999, Ferrucci et al., 1999). A proper understanding of the contribution of determinants to the onset of disability is a prerequisite for preventive interventions in this field.

In this paper we present the incidence of disability in the Rotterdam Study. In addition we present the independent contribution of the main factors that, according to literature, may lead to disability. Other studies have addressed this subject often focusing on one determinant or a distinct group of determinants and correcting for other factors (Peek and Coward, 1999, Seeman et al., 1996, Bruce et al., 1994, Penninx et al., 1999, Ferrucci et al., 1999). In this study we considered all plausible determinants as potential risk factors and treated them as such in the multivariate analyses.