The Effect of Risk Factors on the Duration of Cognitive Impairment: A Multistate Life Table Analysis of the U.S. Health and Retirement Survey

Abstract

Objectives: Improved health may extend or shorten the duration of cognitive impairment by postponing incidence or death. We assessed the duration of cognitive impairment by BMI, smoking and levels of education.

Methods: Multistate life tables estimated the duration of cognitive impairment. Regression models determine the age specific transition probabilities to disease and death in a both genders and three races of the US population from the Health and Retirement Survey (HRS), 1992-2004. Exposures are self-reported BMI, smoking and education, outcome is cognitive functioning determined by the Telephone Interview Cognitive Screen (TICS).

Results: At age 55, white men and women may expect to live respectively 1.7 (1.5; 1.9) and 2.7 (2.4; 2.9) years with cognitive impairment. Black non-Hispanic males and females live 3.7 [2.8,4.6] and 3.7 [3.0,4.5] years longer with cognitive impairment than whites. BMI makes no difference. (Ever) smoking decreases duration of cognitive impairment among men and women with respectively 0.7 [0.3,1.2] and 0.9 [0.5,1.3] years compared to never smokers. Highly educated men and women expect to live respectively 1.1 [0.7,1.4] and 1.9 [1.4,2.4] years with cognitive impairment, lowly educated men and women 2.7 [2.2,3.1] and 3.8 [3.3,4.3] years with cognitive impairment.

Discussion: Our findings confirm the brain reserve hypothesis. While life extension increases the duration of dementia, higher levels of education compress this cognitive disability. Large differences by race remain after controlling for risk factors.