Black-white disparities in functional decline in older persons: the role of cognitive function.

BACKGROUND: Black elders have a greater frequency of functional decline than do white elders. The impact of cognitive function on explaining black-white disparities in functional decline has not been extensively explored.

METHODS: To compare the extent to which different risk domains (comorbidity, smoking, socioeconomic status (SES), self-rated health, and cognitive function) explain more frequent functional decline in black elders, we studied 779 black and 4892 white community-dwelling adults aged 70 and older from the Assets and Health Dynamics Among the Oldest Old (AHEAD), a population-based cohort study begun in 1993. Our primary outcome was worse functional status at 2 years than at baseline. We used logistic regression to compare the unadjusted with the adjusted black-white odds ratios (ORs) after adjusting for each risk domain.

RESULTS: At baseline black participants aged 70-79 had higher rates of smoking, diabetes, and hypertension; lower SES; and worse cognitive function than did white participants (p <.05 for all). The mean cognitive score was 15.7 in black and 21.8 in white participants (p <.01). Black participants had a higher frequency of 2-year functional decline than did white participants (10.9% vs 4.7%; OR = 2.61, 95% confidence interval [CI], 1.69-4.03 adjusted for age and sex). Adjustment for comorbidity and smoking did not significantly change the black-white OR, whereas self-rated health and SES accounted for about half the risk. Adjustment for cognitive function accounted for nearly all the associated decline (OR = 1.10, 95% CI, 0.67-1.79). Among participants aged 80 and over, those who were black had significantly lower risk for functional decline after adjustment for cognitive function (OR = 0.61, 95% CI, 0.38-0.96 vs OR = 1.08, 95% CI, 0.70-1.66 adjusted for age and sex only).

CONCLUSIONS: Cognitive function mediated the higher frequency of functional decline among black elders. Efforts to understand cognitive function may enhance our understanding of black-white disparities in health outcomes.