Income Volatility During Early to Mid-adulthood and 10-year Memory Decline in a Longitudinal Synthetic Cohort.

BACKGROUND: Income volatility may negatively affect midlife cognition, but its impact on cognitive decline is unknown. Lifecourse data to investigate this relationship are lacking; a carefully constructed synthetic cohort can fill this gap.

METHODS: We linked baby boomers from two US cohorts-the National Longitudinal Survey of Youth 1979 (NLSY79, N = 2,871) and the Health and Retirement Study (HRS, N = 5,711)-to create a longitudinal synthetic cohort. In NLSY79, we computed income volatility between 1990 and 2010. In HRS, memory was assessed from 2010 to 2020 (sum of immediate and delayed 10-word recall scores). To link participants across cohorts, each HRS participant was matched to and assigned the income volatility history of their 20 most similar NLSY79 counterparts based on harmonized linking variables measured in 2010 (approximately age 50 in each cohort). In the synthetic cohort, we used confounder-adjusted linear mixed models to estimate the effect of income volatility on memory function and 10-year decline.

RESULTS: Higher income volatility was associated with lower baseline memory function but not decline. Compared with experiencing no income drops ≥25% between surveys, memory scores were lower by 0.11 points (95% CI: -0.40, 0.18) for participants experiencing one drop, 0.32 (95% CI: -0.63, -0.00) for 2 drops, and 0.60 (95% CI: -0.93, -0.27) for ≥3 drops. Results attenuated with adjustment for earlier-life cognition (available only in NLSY79).

CONCLUSION: Income volatility from early to mid-adulthood may impact midlife memory function, but no association with memory decline was observed. Results rely on strong cohort-linking assumptions and may be influenced by unmeasured earlier-life confounders.