Effects of mobility and cognition on maintenance of independence and survival among women in late life

Background: We examined the effects of mobility and cognition on maintenance of independence among women in late life. Methods: Prospective 5-year study of 1,010 independent community-dwelling women (mean age 88.0 years) participating in the Study of Osteoporotic Fractures Year 20 examination (2006-2008). Mobility, ascertained by walk speed, was categorized as good (≥0.9 m/s), intermediate (>0.6 m/s to <0.9 m/s), or poor (≤0.6 m/s). Cognitive status, adjudicated based on neuropsychological tests, was classified as normal or impaired (mild cognitive impairment or dementia). Loss of independence was defined as being unable to perform ≥2 activities of daily living or nursing home residence at 5-year follow-up. Possible outcomes were alive and independent, alive and dependent, and deceased. Results: Four hundred and twenty-three (41.9%) participants were independent at follow-up, whereas 208 (20.6%) were alive but dependent; 379 (37.5%) had died. Compared to women with good mobility, those with slow walk speed were less likely to be independent (risk ratio, [RR] 0.40, 95% confidence interval [CI] 0.29-0.52), after controlling for cognition and other risk factors. Similarly, those with impaired cognition were less likely to be independent, after controlling for walk speed and other risk factors (RR 0.60, 95% CI 0.49-0.71). Women with slow walk speed and impaired cognition were 6-fold less likely to be independent at follow-up compared to those with good walk speed and normal cognition (RR 0.15, 95% CI 0.08-0.23). Conclusions: Both mobility and cognition are associated with maintenance of independence among the oldest old of women even after accounting for each other and other conventional predictors.