Is olive oil good for your heart? A trial and two big cohorts point the same way

Olive oil has better evidence behind its heart-health reputation than most kitchen staples, and it comes from two directions that rarely agree so cleanly: a randomised trial and a pair of very large observational cohorts. Both point the same way, and both are more specific than the marketing — the benefit is modest, it shows up most clearly against certain other fats, and it is bound up with the overall dietary pattern rather than the oil alone.

The trial

The PREDIMED trial, in Spain, assigned 7,447 participants aged 55 to 80 (57 percent women) who were at high cardiovascular risk but had no cardiovascular disease at enrolment to one of three diets: a Mediterranean diet supplemented with extra-virgin olive oil, a Mediterranean diet supplemented with mixed nuts, or a control diet of advice to reduce dietary fat [s1]. Those in the olive-oil group were given free extra-virgin olive oil; the primary end point was a major cardiovascular event — heart attack, stroke or death from cardiovascular causes [s1].

Over a median 4.8 years, a primary end-point event occurred in 288 participants: 96 in the olive-oil group (3.8 percent), 83 in the nut group (3.4 percent) and 109 in the control group (4.4 percent) [s1]. In the intention-to-treat analysis, the hazard ratio was 0.69 (95 percent confidence interval 0.53 to 0.91) for the Mediterranean diet with extra-virgin olive oil, and 0.72 (0.54 to 0.95) for the diet with nuts, compared with the reduced-fat control [s1]. The result carries an asterisk worth stating: the authors withdrew their original 2013 report after finding protocol deviations, including some participants who were not properly randomised, and re-ran the analysis without relying on the assumption that everyone was randomly assigned [s1]. The revised estimates held, and were similar after omitting the 1,588 participants whose group assignments were known or suspected to have departed from the protocol [s1]. It is a trial of a whole dietary pattern, not of olive oil in isolation — but olive oil was the supplement that defined one arm.

The cohorts

The observational evidence comes from two long-running US studies: 61,181 women in the Nurses' Health Study and 31,797 men in the Health Professionals Follow-up Study, all free of cancer, heart disease and stroke at baseline, with diet assessed by questionnaire every four years [s2]. Over 24 years of follow-up the researchers recorded 9,797 cases of cardiovascular disease, including 6,034 coronary heart disease cases and 3,802 strokes [s2].

Compared with people who essentially never used olive oil, those with a higher intake — more than half a tablespoon a day, or more than 7 grams — had a 14 percent lower risk of cardiovascular disease (pooled hazard ratio 0.86, 95 percent confidence interval 0.79 to 0.94) and an 18 percent lower risk of coronary heart disease (0.82, 0.73 to 0.91) [s2]. No significant association was seen for stroke [s2]. Two further findings sharpen the picture. Replacing 5 grams a day of margarine, butter, mayonnaise or dairy fat with the equivalent amount of olive oil was associated with 5 to 7 percent lower risk of cardiovascular disease and coronary heart disease [s2]. But when olive oil was compared with other plant oils combined, no significant association was observed [s2].

What that combination is telling you

Read together, the trial and the cohorts make a coherent and appropriately narrow claim. A Mediterranean pattern anchored by extra-virgin olive oil lowered hard cardiovascular events in a randomised trial [s1], and in large cohorts more olive oil tracked with less heart disease [s2] — with the clearest benefit coming from swapping it in for butter, margarine and other animal or spreadable fats, and little to distinguish it from other plant oils [s2].

That last detail is the one most often lost. The cohort data does not show olive oil to be uniquely protective among plant oils; its edge is largely over the solid and dairy fats it displaces [s2]. And the cohort findings are observational — people who use more olive oil differ in diet and lifestyle in ways that adjustment cannot fully remove — which is exactly why the randomised PREDIMED result matters as corroboration, deviations and all [s1].

None of this is a prescription of a specific daily amount, and swapping fats is one part of cardiovascular risk alongside blood pressure, smoking, activity and lipids. But as far as everyday dietary questions go, "is olive oil good for your heart" is one of the better-supported yeses — with the caveat that most of the benefit is in what it takes off the plate.

Sources

• Primary Prevention of Cardiovascular Disease with a Mediterranean Diet Supplemented with Extra-Virgin Olive Oil or Nuts — New England Journal of Medicine, 2018-06-21
• Olive Oil Consumption and Cardiovascular Risk in U.S. Adults — Journal of the American College of Cardiology, 2020-04-01