The Pace of Memory Decline in Older Adults without a Neurocognitive Disorder: Results from 22 Years of Follow-Up in a Nationally Representative Sample.

Introduction: The pace of cognitive change is one of the major questions in cognitive aging. The Children of the Depression Age (CODA) cohort of the Health and Retirement Study (HRS) is uniquely suited to study cognitive aging because it has a long follow-up (22 years) and a narrow age range at baseline (67-74 years) and presents a unique opportunity to study this topic.

Methods: We examined delayed recall data over the 22 years of follow-up in a nationally representative sample of the USA (HRS-CODA; N = 2,295 at baseline and N = 263 at the final follow-up wave), examining results for the entire sample and omitting participants with self-reported dementia. Data were analyzed using latent growth curve models, adjusting for baseline age, sex, years of education, and race/ethnicity.

Results: Respondents were predominantly female (62%), white (86%), and 71 years old on average at baseline. Our results suggest the pace of normative (defined as the absence of a dementia diagnosis over the follow-up period) memory decline is about -0.05 standard deviations per year (SD/y) but is better characterized by age-specific estimates of -0.04 SD/y, -0.10 SD/y, and -0.15 SD/y for an individual who was 75, 85, and 95, respectively.

Discussion: Memory decline, in the absence of a recognized dementia and without a confounding of baseline age differences and longitudinal age changes, would be present but almost imperceptible to an individual in their eighth decade, but noticeable in their ninth and quite impairing in their tenth decade. Future research is needed to examine other cognitive domains and with more robust measures.