Self-assessed health status, walking speed and mortality in older Mexican-Americans

Background: Self-assessed health status (SAHS) and physical performance measures (in particular, walking speed) are strong predictors of health-related events. Nevertheless, the possible interaction between them in predicting major outcomes has not been clearly explored. Objective: The aim of the study is to evaluate the predictive and additive value for mortality of a SAHS measure and a walking speed test. Methods: Data are from 2,139 Mexican-Americans aged ≥65 years enrolled in the Hispanic Established Populations for Epidemiologic Studies of the Elderly, and followed for 5.8 years. At the baseline visit, participants were asked to answer to the question 'How is your health in general?' presented as a four-level Likert item (i.e., poor, fair, good, excellent). They were also asked to 'walk down and back as fast as it felt safe and comfortable' along an 8-ft track. Cox proportional hazard models, receiver operating characteristic (ROC) curve, and specificity/sensitivity analyses were performed to evaluate the predictive value of SAHS and walking speed for mortality. Results: The mean age of the sample was 72.1 years. Participants reporting 'poor' SAHS were more likely to die compared to those with 'excellent' SAHS, even after adjustment for potential confounders (HR 1.52, 95% CI 1.10-2.10). Similar results were obtained for participants with slow walking speed (<0.29 m/s; HR 1.68, 95% CI 1.27-2.24; reference group: walking speed ≥0.81 m/s). A statistically significant, but weak, correlation between SAHS and walking speed was observed (Pearson's r = 0.069, p = 0.001). No significant differences in areas under curves from ROC analyses were reported for the prediction of mortality when the SAHS and walking speed were tested (alone or in combination). Both tests presented high specificity (≥80%) for the prediction of mortality. Conclusion: SAHS and walking speed are not only significant and independent predictors of mortality in older Mexican-Americans, but also present a similar predictive value. The additive prognostic value of the two measures is limited.