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

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.