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A new study from the Yale-Griffin Prevention Center at Yale University found that high-polyphe­nol extra vir­gin olive oil con­sump­tion improved endothe­lial func­tion in adults at risk of con­tract­ing type 2 dia­betes, while refined olive oil did not.

Endothelial func­tion is a mea­sure of how well blood ves­sels expand when blood flows through them and is an inde­pen­dent pre­dic­tor for car­dio­vas­cu­lar dis­ease.

The researchers decided to con­duct the study after find­ing mixed results from pre­vi­ous stud­ies about the impacts of olive oil con­sump­tion on car­dio­vas­cu­lar health and sought to dif­fer­en­ti­ate the effects of dif­fer­ent types of olive oil.

“While research over the past few years has shown that olive oil can offer con­sid­er­able ben­e­fits to heart health, results of those stud­ies have not always been con­sis­tent,” said Valentine Njike, the assis­tant direc­tor of research and eval­u­a­tion at the Yale-Griffin Prevention Center and lead author of the study.

“This may be due to the fact that the nutri­tional con­tent of olive oil varies,” he added. ​“For exam­ple, all olive oils are rel­a­tively high in monoun­sat­u­rated fat, which is thought to be ​‘heart-healthy,’ but extra vir­gin olive oil con­tains higher lev­els of bio­phe­nols, nat­ural com­pounds that mod­u­late oxida­tive stress, and are thought to slow the pro­gres­sion of car­dio­vas­cu­lar dis­ease.”

For the study, which received fund­ing from Cobram Estate, researchers selected 20 obese, mostly-Caucasian par­tic­i­pants at risk of con­tract­ing type 2 dia­betes. Half of the par­tic­i­pants were men and the other half were women. All par­tic­i­pants had high blood pres­sure and the aver­age age was 56.

At the begin­ning of the study, each par­tic­i­pant had their endothe­lial func­tion mea­sured before con­sum­ing 50 mil­li­liters of either the extra vir­gin olive oil or refined olive oil, which was blended into a yogurt-based smoothie. The par­tic­i­pants then had the endothe­lial func­tion mea­sured again.

After a one-week washout period, the par­tic­i­pants returned and repeated the process with the other type of olive oil. Neither the researchers nor par­tic­i­pants knew which type of oil they were giv­ing or receiv­ing.

“Our study demon­strated that a sin­gle dose of 50 mil­li­liters of high-polyphe­no­lic extra vir­gin olive oil, when com­pared with refined olive oil with­out polyphe­nols, was asso­ci­ated with endothe­lial func­tion improve­ment among indi­vid­u­als at risk for type 2 dia­betes mel­li­tus,” the researchers wrote.

“The acute effects of extra vir­gin olive oil on endothe­lial func­tion observed may be explained by dif­fer­ences in the com­po­si­tion of extra vir­gin olive oil and refined olive oils,” they added.

The researchers attrib­uted the improved endothe­lial func­tion to sev­eral dif­fer­ent polyphe­no­lic con­tents present in the extra vir­gin olive oil, includ­ing nat­u­rally-occur­ring min­er­als and vit­a­mins. These pro­vide anti-inflam­ma­tory and anti-oxi­da­tion prop­er­ties to the oil and are not found in refined olive oils.

While researchers said that the scope of the study was small and more work with larger and more diverse cohorts was needed to con­firm their find­ings, the results demon­strate that the type of olive oil used in future stud­ies should be pre­cisely doc­u­mented.

“There is tremen­dous inter­est in, and lively debate about, the health effects of oils, includ­ing olive oil. Such debates should be resolved with data, and this study makes an impor­tant con­tri­bu­tion by high­light­ing the rel­e­vance of not just the type of oil, but also its qual­ity,” said David Katz, found­ing direc­tor of the Yale-Griffin Prevention Center and co-author of the study.

“We have added to an impres­sive weight of evi­dence indi­cat­ing diverse health ben­e­fits from gen­uine extra vir­gin olive oil,” he added.

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