Physical functioning and mortality in older women:

Abstract

Objective:We tested the hypothesis that the types of activity and the energy equivalent assigned to each activity affect the relationship between self-reported physical functioning and mortality.

Methods:We analyzed the relationship between physical functioning and cardiovascular and noncardiovascular mortality in 1230 women (median age 70 years) observed for 7.5 years. We evaluated five separate scores of physical functioning that differed in the method of scoring the responses. Cox proportional hazard models included baseline age, self-reported physical functioning, medical morbidity, and assessment of health.

Results:For cardiac and noncardiovascular mortality, greater self-reported functioning was associated independently with a decreased hazard of death. The effects of physical functioning were sensitive to the form of the score used; that is, a score based on ordinal responses was associated with a greater reduction in hazard of death difference in survival between high and low function score: Ordinal: −15.2% (95% confidence interval [CI] −25.2–−4.0); dichotomous: −11.6% (95%CI −18.9–−3.9).

Conclusion:There is a consistent relationship between functional limitation and all causes of mortality. The association is sensitive to the form of the score. Future physical function scores should be based on ordinal responses to individual items used in the scores.

Introduction

Physical functioning is generally defined as the relative ease with which a person can perform activities of everyday living (ADL). These activities can range from simple, generic tasks such as pushing, lifting, and carrying items to more complicated activities associated with household maintenance, employment, and driving an automobile. Standard items, originally developed by Nagi and Rosow and Breslau [1], [2], often are used in epidemiologic studies to measure self-reported level of physical functioning in older populations. Respondents typically are asked to report their level of difficulty in the performance of specific tasks that require different combinations of upper- and lower-body strength, mobility, balance, and fine dexterity. Reported limitations in one or more of these tasks form the basis for the classification of disability [3]. One of the most common subsets of items includes questions that deal with pushing and pulling heavy objects, lifting or carrying items over 10 pounds, lifting or carrying items under 10 pounds, walking a city block, and walking up and down stairs without assistance. These items serve as the basis for assessments of probability of future disablement and impaired quality of life [4], [5] and have been shown to predict subsequent risk of death in older populations [6], [7], [8].

Although these are standard items for self-reported functional assessment [1], [2], [4], [9], [10], [11], reported levels of difficulty have been measured and summarized in a variety of ways, and there is no generally agreed upon standard summary protocol [10], [12], [13]. This makes comparisons across studies difficult; furthermore, it is unknown whether differences in the scoring and summarization of levels of difficulty are associated with quantitative differences in the associations between self-reported function and mortality. It also is unknown whether the type of task itself affects the prediction of mortality and specific causes of death. Difficulty in one task (e.g., lifting items over 10 pounds) is treated as the same as difficulty in performance of another task, such as pushing or pulling objects, even though each task may reflect the use of different muscle groups and levels of energy expenditure. Unlike research on physical activity and health [14], [15], estimates of energy expenditure have not been used to distinguish among different functional items and their relationships to future disability and mortality.

We undertook an analysis of the relationship between self-reported physical functioning and mortality in older women. Our hypothesis was that the types of activities included and the energy equivalent assigned to each activity would affect the associations between self-reported physical functioning and mortality. Based on the five functional items described previously, we evaluated several different methods of scoring and summarization of the subjects' responses to create a summary measure of functioning. We included estimates of the energy equivalents associated with each task to determine the effect on the associations with mortality.