Fruit and vegetable intake and cognitive impairment: a systematic review and meta-analysis of observational studies

Background/objectives Epidemiological studies investigating the association between fruit and vegetable consumption and cognitive function have produced inconclusive findings. The aim of this review was to systematically investigate if increased fruit and vegetable consumption is linked with decreased risk of cognitive impairment (CI). Methods We conducted a systematic literature search using four databases (PubMed, Embase, Cochrane Library, and Scopus) in October 2016 and identified cohort and cross-sectional studies, which estimated the risk of CI for fruit and vegetable consumption. The pooled odds ratio (OR) and 95% confidence interval (CI) were estimated by using a random effects model. Results The six studies meeting inclusion criteria offered 10 effect sizes and the total of 17,537 participants in the analysis. Increased fruit and vegetable intake was associated with reduced risk of CI (OR: 0.79; 95% CI: 0.67-0.93; P = 0.006). The subgroup analysis demonstrated that in studies conducted in China (but not in Western countries), the corresponding reduction in risk of CI risk was significant (OR: 0.74; 95% CI: 0.61, 0.89; P = 0.002) and the relationship between fruits, vegetables, and CI did not differ by study design, type of exposure, and gender. Conclusion Increased fruit and vegetable consumption is associated with the reduced risk of CI; however, such association might be dependent on the geographical region. Further prospective studies specifically designed to compare vegetables and fruit varieties, and also to determine the recommended amounts to prevent CI are warranted.