Abstract
Although cross-sectional studies suggest that cognitive aging starts in midlife, few longitudinal studies have documented within-individual declines in cognitive performance before the seventh decade. Learning from repeat testing, or practice effects, can mask the decline in younger cohorts. In women, the menopause transition also affects test performance and can confound estimates of underlying decline. We designed this study to determine if, after controlling for practice effects, the menopause transition, and the symptoms associated with it, there is evidence of cognitive aging in midlife women. We used data from a longitudinal observational study in 2,124 participants from the Study of Women’s Health Across the Nation. Outcomes examined were scores on annual tests of processing speed, verbal episodic memory (immediate and delayed), and working memory. To reduce the impact of practice effects and of the menopause transition, we used the third cognition testing visit as the baseline. Average age at this baseline was 54 years, and the majority of the women were postmenopausal; half the cohort was 2 or more years beyond the final menstrual period. There were 7,185 cognition assessments with median follow-up time of 6.5 years. In mixed effects regression, adjusted for practice effects, retention, menopause symtoms (depressive, anxiety, vasomotor, and sleep disturbance), and covariates, scores on 2 of 4 cognition tests declined. Mean decline in cognitive speed was 0.28 per year (95% confidence interval [CI] 0.20 to 0.36) or 4.9% in 10 years, and mean decline in verbal episodic memory (delayed testing) was 0.02 per year (95% CI: 0.00 to 0.03) or 2% in 10 years. Our results provide strong, longitudinal evidence of cognitive aging in midlife women, with substantial within-woman declines in processing speed and memory. Further research is needed to identify factors that influence decline rates and to develop interventions that slow cognitive aging.
Highlights
Decline in cognitive functioning is common in older ages [1,2], there is controversy about whether there is significant decline in cognitive abilities in midlife
In midlife women going through the menopause transition (MT), at least 2 cohorts found no evidence of cognitive aging; instead they documented significant improvements in performance over multiple years [8,9]
The average, within-woman rate of decline in processing speed was essentially identical to the average, between-women difference by age at time of final menstrual period (FMP) (0.28 per year vs. 0.31 per year)
Summary
Decline in cognitive functioning is common in older ages [1,2], there is controversy about whether there is significant decline in cognitive abilities in midlife. One large study that assessed cognitive performance 3 times over 10 years, did demonstrate longitudinal declines in cognitive performance in midlife, albeit at a slower rate than that of older adults [7]. Similar improvements in cognitive performance in midlife have been documented in the Baltimore Longitudinal Study of Aging, and attributed to learning or practice effects from repeat testing [10]. The phenomenon of learning from repeat testing has long been recognized as hampering the estimation of underlying longitudinal change in cognitive performance, and is thought to lead to underestimation—even masking— of true decline [4,6,10,11,12]
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