Among vitamin B12 deficient older people, high folate levels are associated with worse cognitive function: Combined data from three cohorts

Background: Folate fortification of food aims to reduce the number of babies born with neural tube defects, but has been associated with cognitive impairment when vitamin B12 levels are deficient. Given the prevalence of low vitamin B12 levels among the elderly, and the global deployment of food fortification programs, investigation of the associations between cognitive impairment, vitamin B12, and folate are needed. Objective: To investigate the associations of serum vitamin B12, red cell folate, and cognitive impairment. Methods: Data were collected on 1,354 subjects in two studies investigating cognitive impairment, and from patients attending for assessment or management of memory problems in the Barwon region of south eastern Australia between 2001 and 2011. Eligible subjects who had blood measurements of vitamin B12 and red cell folate taken within six months of cognitive testing were included. Subjects with stroke or neurodegenerative diseases other than Alzheimer's disease were excluded. A Mini-Mental State Examination score of <24 was used to define impaired cognitive function. Results: Participants with low serum vitamin B12 (<250 pmol/L) and high red cell folate (>1,594 nmol/L) levels were more likely to have impaired cognitive performance (adjusted odds ratio (AOR) 3.45, 95% confidence interval (CI): 1.60-7.43, p = 0.002) when compared to participants with biochemical measurements that were within the normal ranges. Participants with high folate levels, but normal serum vitamin B12, were also more likely to have impaired cognitive performance (AOR 1.74, 95% CI: 1.03-2.95, p = 0.04). Conclusions: High folate or folic acid supplements may be detrimental to cognition in older people with low vitamin B12 levels. This topic is of global significance due to the wide distribution of food fortification programs, so prospective studies should be a high priority.