There was no dose- response effect; the largest impairment was found with 0–50 mg/kg of d-galactose (2.25 SMD, 95% CI, -1.75 to 2.76) and the smallest with 400–1250 mg/kg (1.73 SMD, 95% CI, 1.15 to 2.31: χ2 for difference = 304.26, Τ2 = 1.07, I2 = 81.9%, d.f. = 55, p<0.0005; Fig 3B).