Reference
Martínez-González MÁ, Toledo E, Arós F, et al; PREDIMED Investigators. Extra virgin olive oil consumption reduces risk of atrial fibrillation: the PREDIMED (Prevención con Dieta Mediterránea) trial. Circulation. 2014;130(1):18-26.
Design
This study is the current product of data from the Prevención con Dieta Mediterránea (PREDIMED) Trial. PREDIMED was a large multicenter trial conducted in Spain that randomly assigned participants who were at high cardiovascular risk but with no cardiovascular disease at enrollment to 1 of 3 diets with food supplementation.
Participants
All study participants were at high risk for cardiovascular disease (CVD): about half were taking angiotensin-converting-enzyme inhibitor inhibitors, one-fifth were taking diuretics, slightly more than one-fourth were taking other antihypertensive agents, two-fifths were taking a statin lipid-lowering drug, and more than one-third were taking an oral hypoglycemic agent or insulin. Of the 7447 participants in the larger cohort, 6705 were without prevalent atrial fibrillation (AF) at the start of the trial.
Study Medication and Dosage
Participants in the PREDIMED Trial were randomized to 1 of 3 diets: a Mediterranean diet supplemented with 4 T per day of extra-virgin olive oil; a Mediterranean diet supplemented with 30 g per day of a mixture of nuts (50% walnuts, 25% almonds, and 25% hazelnuts); or a low-fat control diet. The participants in the Mediterranean diet arms of the study were supplied with free extra virgin olive oil or nuts depending on their assigned group. The control group on the low-fat diet was given nonfood gifts. Blood biomarkers were monitored to confirm that the study participants were consuming their nuts or olive oil; hydroxytyrosol measured olive oil consumption, and alpha-linolenic acid measured nut consumption.
Outcome Measures
The primary outcomes tracked in the initial PREDIMED Trial were a composite of stroke, myocardial infarction, or death from cardiovascular disease. The study was stopped early, in December 2010, after only 4.8 years because of early evidence that the Mediterranean arms of the study were showing clear benefit. This current study uses data from 6705 of the participants who were adequately and systematically assessed for AF during the study.
Key Findings
During 4.7 years of follow-up, 72 new cases of AF were observed in participants following the Mediterranean diet with added extra virgin olive oil group, 82 cases in the Mediterranean diet with mixed nuts group, and 92 in the control group. Compared to the control group that was instructed only to follow a low-fat diet, the group consuming the Mediterranean diet with extra virgin olive oil had significantly reduced risk of AF (hazard ratio [HR]: 0.62; 95% confidence interval [CI]: 0.45-0.85). The decrease in AF in the group following the Mediterranean diet with nuts did not reach statistical significance (HR: 0.89; 95% CI: 0.65-1.20).
Practice Implications
One in 4 people will suffer from AF at some point in their lives.1 Thus any intervention that reduces occurrence will be of benefit to a large number of patients. While lifestyle factors such as diet are recognized as important in preventing other CVDs, no such strategies have been shown to impact AF.2 Thus the findings from this study are striking; simply using extra virgin olive oil may be beneficial to the lives of many of patients.
The differences in risk of atrial fibrillation between groups would appear to be due to the type of olive oil: regular vs extra virgin.
This is not the first or only good news to reach us from the PREDIMED Trial. Earlier publications gleaned from data derived from this cohort reported that individuals in the nut or extra virgin olive oil group had a 30% lower risk of CVD incidents.3 Another PREDIMED study reported that the nut group participants showed significantly less cognitive decline than the control group. Still another study showed that those individuals in the nut group had longer life spans.
This current paper appears to be the first to assess the impact of extra virgin olive oil on AF. Mattioli et al, in their 2013 case-control study, found an inverse association between adherence to a Mediterranean diet and AF. Although their “dietary score” included high olive oil consumption as 1 component, no direct estimate of extra virgin olive oil consumption and risk of AF was reported.4
While the control group in these PREDIMED trials was told to follow a low-fat diet and they were compliant initially, over the course of the study, most participants reverted to their “normal” diet, which, because they lived in Spain, differed only slightly from the diet prescribed to the Mediterranean diet group. In fact, the only significant changes made by the 2 Mediterranean diet groups were in fish and bean consumption; fish consumption increased by 0.3 serving per week and bean consumption by 0.4 servings per week in comparison with the control group. No other changes reached statistical significance, except for extra virgin olive oil or nut consumption.
It is unlikely that eating a fraction of a portion of either fish or beans per week would impact risk of AF. Likewise, the benefits should not be attributed to changes in overall fat consumption. The control group, although counseled repeatedly to follow a low-fat diet, did not make dramatic changes. Their percentage of total energy in the diet from fat dropped nonsignificantly from 39% to 37% over the course of the trial.3
All groups consumed a lot of olive oil; 1 year into the study, nearly 92% of the low-fat diet control group reported that olive oil was their primary culinary fat. After 5 years, the percentage had increased to more than 96%. More than 58% of the control group, on the supposedly low-fat diet, reported consuming more than 4 T of olive oil per day. The differences in risk of AF between groups would appear to be due to the type of olive oil: regular vs extra virgin.
If this study is really reporting the impact of extra virgin olive oil vs regular olive oil, it is reasonable to assume that having our patients switch from soybean oil, the most common oil consumed in the United States, to extra virgin olive oil might have a greater impact than the one seen in this analysis.
