Cognitive status and incident disability in older Mexican Americans: findings from the Hispanic established population for the epidemiological study of the elderly.

ABSTRACT

OBJECTIVE: To determine the effects of baseline cognitive function on incidence of disability in activities of daily living (ADL) in initially non-disabled Mexican-American elderly over a 7-year period. DESIGN: A prospective cohort study. SETTING: Southwestern United States Texas, California, Arizona, New Mexico, and Colorado. PARTICIPANTS: A population-based sample of Mexican Americans aged 65 and over who completed the Mini-Mental State Examination (MMSE) and other relevant variables at baseline. The sample at baseline consisted of 2731 subjects, of which 2431 were non-ADL disabled. MEASUREMENTS In-home interviews in 1993-94, 1995-96, 1998-99, and 2000-2001 assessed sociodemographic variables, selected medical conditions (stroke, cancer, diabetes, arthritis, and hip fracture), cognitive function, depressive symptomatology, and ADLs. RESULTS: In a Cox proportional regression analysis, a significant relationship was evident between MMSE score at baseline and risk of incident ADL disability over a 7-year period. Among non-disabled subjects at baseline, the hazard ratio of any new ADL limitation was 1.58 (95% CI, 1.18-2.12) for those with impaired cognition (MMSE score 0-21), 1.38 (95% CI, 1.04-1.82) for low normal cognition (MMSE score 22-24), and 1.30 (95% CI, 1.02-1.66) for normal cognition (MMSE score 25-28) when compared to subjects with high-normal cognition (MMSE score 29-30), adjusting for sociodemographic variables, presence of selected medical conditions and depressive symptoms at baseline. Similar results were also found when MMSE score was used as a continuous variable. Among non-disabled subjects at baseline, each unit increase in MMSE score decreased the risk of onset of any ADL limitation over a 7-year follow-up period, controlling for relevant variables at baseline (HR=0.97; 95% CI, 0.95-0.99). CONCLUSION: Low MMSE score was associated with increased risk for incident ADL disability over a 7-year period in older Mexican Americans. Given the social, economic, and health impact of cognitive impairment, these findings suggest a need to develop effective intervention programs that delay or prevent the onset of cognitive and ADL disability in the elderly.