Trends in the prevalence and mortality of cognitive impairment in the United States: Is there evidence of a compression of cognitive morbidity?

Background: Recent medical, demographic, and social trends might have had an important impact on the cognitive health of older adults. To assess the impact of these multiple trends, we compared the prevalence and 2-year mortality of cognitive impairment (CI) consistent with dementia in the United States in 1993 to 1995 and 2002 to 2004. Methods: We used data from the Health and Retirement Study (HRS), a nationally representative population-based longitudinal survey of U.S. adults. Individuals aged 70 years or older from the 1993 (N = 7,406) and 2002 (N = 7,104) waves of the HRS were included. Cl was determined by using a 35-point cognitive scale for self-respondents and assessments of memory and judgment for respondents represented by a proxy. Mortality was ascertained with HRS data verified by the National Death Index. Results: In 1993, 12.2% of those aged 70 or older had CI compared with 8.7% in 2002 (P < .001), Cl was associated with a significantly higher risk of 2-year mortality in both years. The risk of death for those with moderate/severe CI was greater in 2002 compared with 1993 (unadjusted hazard ratio, 4.12 in 2002 vs 3.36 in 1993; P = .08; age- and sex-adjusted hazard ratio, 3.11 in 2002 vs 2.53 in 1993; P = .09). Education was protective against CI, but among those with CI, more education was associated with higher 2-year mortality. Conclusions: These findings support the hypothesis of a compression of cognitive morbidity between 1993 and 2004, with fewer older Americans reaching a threshold of significant CI and a more rapid decline to death among those who did. Societal investment in building and maintaining cognitive reserve through formal education in childhood and continued cognitive stimulation during work and leisure in adulthood might help limit the burden of dementia among the growing number of older adults worldwide. (c) 2008 The Alzheimer's Association. All rights reserved.