Docosahexaenoic acid supplementation in age-related cognitive decline: a systematic review and meta-analysis

To investigate the role of DHA supplementation in preventing age-related cognitive decline (ARCD) in individual cognitive domains by conducting systematic review and meta-analysis. Relevant clinical trials were systematically searched at Medline, PubMed, Scopus, Cochrane, ProQuest, and Embase databases since inception to June 2018. The PRISMA guidelines were adhered for data abstraction, quality assessment, and validation of included studies. Study details such as participant characteristics, DHA supplementation, and cognitive function outcome measures, i.e., memory, attention, working memory, and executive function, were extracted to perform meta-analysis according to the Cochrane guidelines. Additional meta-regression and subgroup analyses were performed to detect confounding variables and sensitivity of results, respectively. Ten studies including 2327 elderly individuals were part of the final results. Study exhibited minimal or no pooled incremental effects on memory (0.22, 95%CI = − 0.17 to 0.61, I2 = 94.36%), attention (0.1, 95%CI = − 0.04 to 0.25, I2 = 32.25%), working memory (0.01, 95%CI = − 0.10 to 0.12, I2 = 0%), and executive function (0.03, 95%CI = − 0.05 to 0.11, I2 = 78.48%) among the DHA-supplemented group. The results from standard mean difference between the groups, on memory (0.08, 95%CI = − 0.12 to 0.28, I2 = 76.82%), attention (0.04, 95%CI = − 0.09 to 0.23, I2 = 42.63%), working memory (− 0.08, 95%CI = − 0.26 to 0.10, I2 = 37.57%), and executive function (0.17, 95%CI = − 0.01 to 0.36, I2 = 78.48%) were similar to the results of pooled incremental analysis. Lastly, results remained unaffected by sensitivity and sub-group analyses. Current pieces of evidence do not support the role of DHA supplementation, in preventing/retarding ARCD of memory, executive function, attention, and working memory. Protocol registered at PROSPERO (ID: PROSPERO 2018 CRD42018099401).