Dynamic patterns of anemia and cognitive function: a longitudinal cohort study based on the China Health and Retirement Longitudinal Study

BACKGROUND: Anemia is associated with cognitive decline, but the influence of its temporal patterns on cognitive trajectories remains unknown. This study investigated the longitudinal association between dynamic anemia patterns (persistent, intermittent, never) and cognitive function in middle-aged and older Chinese adults. METHODS: We analyzed data from 6,364 participants aged ≥ 45 years in the China Health and Retirement Longitudinal Study (2011-2020). Based on 2011 and 2015 hemoglobin measurements, participants were categorized as never, intermittent, or persistent anemia. Linear mixed-effects models assessed associations with cognitive function. Sensitivity analyses included multiple imputation, varying anemia thresholds, and inverse probability weighting. RESULTS: Based on hemoglobin levels in 2011 and 2015, 4,769 (74.9%) participants had never anemia, 1,201 (18.9%) had intermittent anemia, and 394 (6.2%) had persistent anemia. In linear mixed-effects models adjusted for age and sex, both intermittent anemia (β = -0.31, 95% CI: -0.56 to -0.06, P = 0.016) and persistent anemia (β = -0.47, 95% CI: -0.88 to -0.06, P = 0.025) were associated with lower baseline cognitive scores compared to the never anemia group. However, only persistent anemia was associated with a faster rate of cognitive decline over time (time × persistent anemia: β = -0.057, 95% CI: -0.100 to -0.014, P = 0.009), whereas the interaction for intermittent anemia was not significant (time × intermittent anemia: β = 2.18e-5, 95% CI: -0.025 to 0.025, P = 0.999). Sensitivity analyses, including multiple imputation and inverse probability weighting, and analyses using different diagnostic thresholds produced directionally consistent results, with more lenient thresholds attenuating the effects; the WHO threshold demonstrated the strongest discriminatory power. Transition pattern analysis revealed that, compared to the persistently normal group, the persistent anemia and incident anemia groups maintained lower cognitive levels throughout follow-up, whereas anemia remission was associated with significant, though incomplete, cognitive improvement. CONCLUSIONS: Persistent anemia is associated with the most rapid cognitive decline, while intermittent anemia is associated with lower baseline cognition. Improvement in anemia status may confer cognitive benefits, highlighting the importance of dynamic anemia monitoring and timely intervention in cognitive health management.