Vitamin C Status and Cognitive Function: A Systematic Review

Abstract

Vitamin C plays a role in neuronal differentiation, maturation, myelin formation and modulation of the cholinergic, catecholinergic, and glutaminergic systems. This review evaluates the link between vitamin C status and cognitive performance, in both cognitively intact and impaired individuals. We searched the PUBMED, SCOPUS, SciSearch and the Cochrane Library from 1980 to January 2017, finding 50 studies, with randomised controlled trials (RCTs, n = 5), prospective (n = 24), cross-sectional (n = 17) and case-control (n = 4) studies. Of these, 36 studies were conducted in healthy participants and 14 on cognitively impaired individuals (including Alzheimer's and dementia). Vitamin C status was measured using food frequency questionnaires or plasma vitamin C. Cognition was assessed using a variety of tests, mostly the Mini-Mental-State-Examination (MMSE). In summary, studies demonstrated higher mean vitamin C concentrations in the cognitively intact groups of participants compared to cognitively impaired groups. No correlation between vitamin C concentrations and MMSE cognitive function was apparent in the cognitively impaired individuals. The MMSE was not suitable to detect a variance in cognition in the healthy group. Analysis of the studies that used a variety of cognitive assessments in the cognitively intact was beyond the scope of this review; however, qualitative assessment revealed a potential association between plasma vitamin C concentrations and cognition. Due to a number of limitations in these studies, further research is needed, utilizing plasma vitamin C concentrations and sensitive cognitive assessments that are suitable for cognitively intact adults.

Keywords: Alzheimer’s; MMSE; ascorbic acid; central nervous system; cognition; dementia; vitamin C.

Figure 1

Flow chart of steps in systematic review.

Figure 2

Scatterplot of baseline mean MMSE scores against blood vitamin C concentrations. Blue circles represent cognitively impaired groups of participants, and green triangles and crosses represent cognitively intact groups (triangles: direct plasma vit C measure, cross: converted from FFQ). No correlation analyses were conducted on the cognitively intact data points. The blue line represents the correlation slope amongst the studies of cognitively impaired groups of participants (r_s (11) = 0.009, p = 0.98). Key: Ref = study reference, * Not included in the analysis, AD = Alzheimer’s disease, CSF = Cerebral Spinal Fluid, FFQ = Food Frequency Questionnaire; MCI = mild cognitive impairment, mg/day = milligram per day, VaD = Vascular dementia, Con = concentration, MMSE = Mini Mental State Examination.