Published in the journal Frontiers in Nutrition, the review gathered data from a total of 11 randomized controlled trials (RCTs), cross-sectional studies, cohort studies and case-control studies identified though a systematic search of the Web of Science, Scopus, PubMed and Google Scholar data bases through Aug.11, 2023.
“The cohort studies and RCTs consistently found that olive oil consumption had a favorable effect on cognitive performance across a number of cognitive domains over time,” the researchers wrote. “Similarly, all of the cross-sectional studies reported that the consumption of olive oil was positively associated with cognitive health.”
Considerable heterogeneity in the population characteristics, interventions/exposures, study designs and outcome measures across the included studies prevented the research team from conducting a meta-analysis.
EVOO and cognitive health
Extra virgin olive oil (EVOO) is rich in a variety of phenolic compounds known for their anti-inflammatory and antioxidant properties. Its neuroprotective effects are mostly attributed to the polyphenol oleuropein-aglycone, a compound generated when glucosidase is released during the olive crushing process.
“Oleuropein aglycone counteracts amyloid aggregation and toxicity affecting different pathways: amyloid precursor protein processing, amyloid-β peptide and tau aggregation, autophagy impairment, and neuroinflammation,” according to a 2016 study carried out by researchers at the University of Balearic Islands, Spain.
Hydroxytyrosol, another phenolic byproduct of olive oil extraction process with potent antioxidant bioactivity, has also drawn attention due to its ability to cross the blood–brain barrier and protect brain cells from lipid peroxidation.
Of all the olive oils, EVOO is considered the highest quality since the cold mechanical extraction without solvents or other refining methods preserves the most potent antioxidant and anti-inflammatory components of the olive.
The researchers identified four cross-sectional studies, four cohort studies and three RCTs that met inclusion criteria of the 934 results returned by the database search. Populations studied were from France, Germany, Greece, Morocco, Poland and Spain, with sample sizes ranging from 50 to 6,947 participants. Follow-up for the RCTs and cohort studies was between one and 10 years.
Across studies, cognitive function was assessed using a variety of tests that measured attention, global cognition, processing speed, episodic memory, executive functioning and working memory.
“The findings from the RCTs indicated that the consumption of olive oil could increase cognitive performance in almost all cognitive domains measured,” the researchers wrote.
The MICOIL Pilot Study, for example, found that the intake of Greek high phenolic early harvest EVOO and moderate phenolic EVOO, along with Mediterranean Diet adherence for one year, in people with mild cognitive impairment (MCI) were correlated with improvements to global cognition, letter fluency and MCI stability.
Similarly, Spanish researchers on the earlier PREDIMED-NAVARRA trial linked an EVOO-rich Mediterranean Diet with superior cognition, particularly as related to fluency and visual and verbal memory, after 6.5 years of nutritional intervention. Another study found that the addition of a low dose of EVOO to the Mediterranean Diet improved cognitive performance in 180 southern Italians over the age of 65.
Noting limitations including the heterogeneity in study designs and reported outcomes, possible omission of eligible studies, lack of participant information, risk of bias, differences in cognitive measurement tools and olive oil measurements, the review called for further large-scale investigations into the causal relationship between olive oil and cognitive performance.