Risk factors of functional disability among community-dwelling elderly people by household in Japan: a prospective cohort study

BACKGROUND Although the number of elderly people needing care is increasing rapidly in the home setting in Japan, family size and ability to provide such support are declining. The purpose of this study was to identify the risk factors of functional disability by household composition among community-dwelling elderly people. METHODS A total of 1347 elderly people aged 70 years and over participated in a baseline geriatric health examination for this prospective cohort study. In the health examination, we conducted an interview survey using a questionnaire in July 2004 and July 2005. Questionnaire items covered the following: age, sex, household, medical history, instrumental activities of daily living, intellectual activity, social role, Motor Fitness Scale, falls experienced during the past year, Dietary Variety Score, frequency of going outdoors, cognitive impairment, and depressive status. We defined the occurrence of functional disability as certification for long-term care needs of the subjects. The certification process started with a home visit for an initial assessment to evaluate nursing care needs using a questionnaire on current physical and mental status. The onset of functional disability was followed from July 2004 to March 2011. Cox proportional hazard regression analysis was used to estimate the risk factors related to the onset of functional disability, adjusted for age and sex. RESULTS Of the 1084 participants, 433 were male (39.9%), and the average age was 77.8 (standard deviation, 5.4). Up to March 2011, functional disabilities occurred in 226 participants (20.9%). Elderly people living only with their children demonstrated a significantly higher risk for functional disability than the three-generation household group (hazard ratio, 1.61; 95% confidence interval, 1.08-2.40). The risk factors for functional disability varied according to household group. CONCLUSIONS In Japan, the number of vulnerable households with elderly people in need of care has increased steadily over the years. Appropriately identifying the risks related to functional disability requires a means of assessment that takes the household composition into consideration.