Background: This paper reports the association between self-reported diseases and impairments and 2-year onset of disability in a prospective study of people aged 65 years or older in five urban and rural centers in England and Wales (Medical Research Council Cognitive Function and Ageing Study; MRC-CFAS).

Methods: We initially reviewed risk factors for onset of disability in 35 prospective studies of functional decline in older people published in 1998-2001. In the present study, disability was defined as requiring help from another person at least several times a week and was assessed by dependency in activities of daily living. Polytomous and bivariate logistic regression models were fitted for onset of disability and mortality among those nondisabled at baseline (n=7913), adjusting for age, sex, and sociodemography.

Results: Among prevalent conditions, arthritis (population-attributable risk 11.4%) and cognitive impairment indicated by a Mini-Mental State Examination score of <or=21 (population-attributable risk 6.8%) were powerful predictors of incident disability. Baseline cognitive impairment, stroke, treated diabetes, chronic airways obstruction, coronary heart disease, and treated hypertension were significantly associated with both incident disability and mortality, whereas Parkinson's disease, eyesight problems, and arthritis were statistically significant disabling conditions not associated with mortality. Stroke, heart attack, cognitive impairment, eyesight problems, and hearing problems were newly occurring conditions significantly associated with onset of disability.

Conclusions: Cognitive impairment, arthritis, followed by stroke, and problems with vision have major impact on population disability at older ages. Both prevalent and incident conditions must be considered as risk factors to accurately assess potential benefits from prevention.