PMCH and anemia: Specifically, no significant causal effects were observed between MCH and reaction time, numeric memory, or prospective memory, while genetically predicted higher MCH was associated with relatively higher verbal–numeric reasoning (OR 1.033, 95% CI 1.005–1.061, P = 0.037, I2 = 16.59%) (Fig. 2 and Table S6), implying that anemia was associated with increased cognitive function.