Factors Influencing Improvement and Decline in Cognition in Elderly Canadians, in Relation to Mortality

Nader Fallah, Dalhousie University
Arnold B. Mitnitski, Dalhousie University
Laura E. Middleton, Dalhousie University
Kenneth Rockwood, Dalhousie University

We investigated five-year changes in cognition (including improvement and decline) in relation to age, sex, education and exercise levels and how these changes affect mortality. The data came from the Canadian Study of Health and Aging (n = 8403, 60.7% women). Cognitive states were defined as errors in the Modified Mini-Mental State Examination (3MS) score. Both improvement and declines were modeled in a unified way using a four-parameter truncated Poisson distribution. In contrast to conventional approaches, our model let us analyze how different risk factors affect cognition to any degree, and simultaneously survival. We found that higher education is beneficial for cognitive function both in men and women but does not improve survival. Exercise was beneficial for everybody but differently by sex: women had a survival advantage compared with men, but men most benefited in cognitive functioning. The exceptionally high fit suggests that these findings are reliable.