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

Langa, Kenneth M.; Larson, Eric B.; Karlawish, Jason H.; Cutler, David M.; Kabeto, Mohammed U.; Kim, Scott Y.; Rosen, Allison B.

doi:10.1016/j.jalz.2008.01.001

« Previous Next »Alzheimer's & Dementia: The Journal of the Alzheimer's Association
Volume 4, Issue 2 , Pages 134-144, March 2008

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

Kenneth M. Langa
- Division of General Medicine, Department of Medicine, University of Michigan, Ann Arbor, MI, USA
- Veterans Affairs Center for Practice Management and Outcomes Research, Ann Arbor, MI, USA
- Institute for Social Research, University of Michigan, Ann Arbor, MI, USA
- Corresponding author. Tel.: 734-615-8341; Fax: 734-936-8944.
Eric B. Larson
- Center for Health Studies, Group Health Cooperative of Puget Sound, Seattle, WA, USA
Jason H. Karlawish
- Department of Medicine, Division of Geriatric Medicine, University of Pennsylvania, Philadelphia, PA, USA
David M. Cutler
- Department of Economics, Harvard University, and the National Bureau of Economic Research, Cambridge, MA, USA
Mohammed U. Kabeto
- Division of General Medicine, Department of Medicine, University of Michigan, Ann Arbor, MI, USA
Scott Y. Kim
- Department of Psychiatry, Bioethics Program, and Center for Behavioral and Decision Sciences in Medicine, University of Michigan, Ann Arbor, MI, USA
Allison B. Rosen
- Division of General Medicine, Department of Medicine, University of Michigan, Ann Arbor, MI, USA
- Veterans Affairs Center for Practice Management and Outcomes Research, Ann Arbor, MI, USA

published online 27 February 2008.

Abstract

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. CI 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). CI 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.

Keywords: Dementia, Epidemiology, Cardiovascular disease, Education