Better Cognition in New Birth Cohorts of 70 Year Olds, But Greater Decline Thereafter.

Objectives: To evaluate birth cohort differences in level of cognition and rate of change in old age.

Methods: Data were drawn from three population-based Swedish samples including age-homogenous cohorts born 1901/02, 1906/07, and 1930, and measured on the same cognitive tests at ages 70, 75, and 79 as part of the Gerontological and Geriatric Populations Studies in Gothenburg (H70). We fitted growth curve models to the data using a Bayesian framework and derived estimates and inferences from the marginal posterior distributions.

Results: We found moderate to large birth cohort effects in level of performance on all cognitive outcomes. Later born cohorts, however, showed steeper linear rate of decline on reasoning, spatial ability, and perceptual- and motor-speed, but not on picture recognition memory and verbal ability.

Discussion: These findings provide strong evidence for substantial birth cohort effects in cognition in older ages and emphasize the importance of life long environmental factors in shaping cognitive aging trajectories. Inferences from cognitive testing, and standardization of test scores, in elderly populations must take into account the substantial birth cohort differences.