Homocysteine, folate, and vitamin B-12 and cognitive performance in older Chinese adults: findings from the Singapore Longitudinal Ageing Study

BACKGROUND: The relations of elevated homocysteine, low folate, and vitamin B-12 with cognitive performance in nondemented elderly are not well established. Limited research data suggest differential effects of homocysteine and folate on specific cognitive domains. OBJECTIVE: The aim was to examine the independent associations of homocysteine, folate, and vitamin B-12 with cognitive performance in high-functioning elderly Chinese. DESIGN: Homocysteine, folate, and vitamin B-12 concentrations were measured in fasting blood samples of 451 Chinese aged >or=55 y with Mini-Mental State Examination scores >or=24 and who were considered fully independent based on Activities of Daily Living score. Cognitive functions were assessed by a neuropsychological test battery. Independent associations (standardized beta) were determined in multiple linear regression models that simultaneously controlled for potential confounders. RESULTS: Log-transformed homocysteine was inversely associated with performance on Block Design (beta = -0.319, P = 0.006) and the written Symbol Digit Modality Test (beta = -0.129, P = 0.031). Log-transformed folate was significantly associated with Rey Auditory Verbal Learning Test delayed recall (beta = 0.139, P = 0.010), verbal learning (beta = 0.112, P = 0.038), percentage of forgetting (beta = -0.139, P = 0.013), and the Categorical Verbal Fluency test (beta = 0.104, P = 0.042). Vitamin B-12 was not significantly associated with any cognitive test score. CONCLUSIONS: In this high-functioning elderly Chinese population, elevated homocysteine is associated with deficits in constructional ability and processing speed and folate is associated with measures of episodic memory and language. Our results provide support for differential effects of homocysteine and folate on specific cognitive functions.