Dementia and physical disability as competing risks for mortality in a community-based sample of the elderly Japanese

To examine whether an excess mortality due to dementia is independent of coexisting physical disability, a probability-sample of the non-institutionalized elderly (n = 3,308) living in Sendai City, Japan was followed between 1988 and 1991. Of those, 128 were diagnosed as dementia in 1988 by psychiatrists, using Diagnostic and Statistical Manual of Mental Disorders, Third Edition-Revised as a diagnostic standard. Information on the ability to perform activities of daily living (ADL) was collected by self-report of the study subjects in 1988 baseline survey. The survival status was investigated three years later. The risks of dementia and co-existing ADL disability for mortality was examined by Cox proportional hazard models. The results indicated that the relation between dementia and mortality was two-fold, depending upon the physical functions. Dementia increased the risk for mortality among those without ADL disability, but it did not so among those with ADL disability, rather ADL function was a stronger predictor for mortality among the latter individuals. Prevention and treatment of physical disability would be important for improving the survival of the demented people.