Dietary interventions and cognition: A systematic review of clinical trials

Prevalence of Alzheimer's Disease and other forms of dementia is increasing in accordance with the increase of life expectancy and the resulting world population aging, while an effective pharmaceutical treatment is pending. These facts underline the need for development of targeted interventions that could decrease the incidence of dementia. Dietary supplementation, especially sources of ω-3 fatty acids and polyphenols such as fish oil and blueberries respectively, have been reported to have a beneficial effect on cognitive functioning. The aim of this review is to summarize the most recent findings of clinical studies investigating the effect of dietary supplementation on cognitive performance and identify potential effective interventions. For this purpose, PubMed, Scopus and Google Scholar research was conducted and a total of ten studies met the selection criteria. Four of these studies investigated the effect of ω-3 fatty acid supplementation. Two of these presented significant benefits in certain domains of cognitive functions (such as working memory, space imagery efficiency perceptual speed), in full scale IQ as well as prevention of hippocampal atrophy while the remaining two did not report any improvements. Two more studies investigated the effect of polyphenol supplementation and reported minor benefits in spatial memory as well as enhanced stimulation of certain brain regions. One study compared the effect of fish oil and blueberry supplementation as well as their combination and presented cognitive benefits for both fish oil and blueberries but not for their simultaneous administration. Finally, three more studies investigated the effect of DW 2009 soybean, ashwagandha and a nutraceutical formulation and reported cognitive benefits in attention, memory and global cognition respectively for their intervention groups. In total, eight studies investigated interventions on people with Mild Cognitive Impairment or Subjective Cognitive Impairment and all of them reported significant cognitive benefits in some cognitive domains. On the contrary, the remaining two studies included individuals with diagnosed dementia reported minimal to hardly any benefits. Conclusively, the interventions of the studies reviewed seem promising for individuals at risk of dementia, but not for those who are already diagnosed with dementia. However, further research is required to validate their effect as well as determine recommended doses.