Three-City Study: Intensive Olive Oil Use Linked to 41% Lower Stroke Risk

This prospective cohort study from three French cities (Bordeaux, Dijon, and Montpellier) followed 7,625 adults aged 65 and older to test whether olive oil consumption was associated with stroke incidence. Published in Neurology, the analysis found that intensive olive oil users -- those who used olive oil for both cooking and dressing -- had a 41% lower risk of incident stroke compared with never-users. A secondary biomarker analysis showed that participants in the highest tertile of plasma oleic acid had a 73% lower stroke risk, providing biological confirmation of the dietary signal.

Why This Study Matters

Stroke is the second leading cause of death worldwide and a major cause of disability in elderly adults. Most stroke prevention research focuses on blood pressure control, anticoagulation, and statin therapy -- pharmacologic interventions. Dietary research on stroke specifically (as opposed to general cardiovascular outcomes) is comparatively thin, and most of the existing data comes from cohorts where stroke is bundled with other CVD endpoints rather than analyzed separately.

The Three-City Study was designed to address that gap in elderly French adults. It enrolled 9,294 participants aged 65+ from three French cities, captured baseline dietary intake, and followed participants prospectively for cerebrovascular events validated by an expert committee. The analysis published here focused on 7,625 participants without baseline history of stroke.

The study did something unusual: it didn't just rely on self-reported intake. In a subsample of 1,245 participants, the researchers measured plasma oleic acid -- a biomarker of olive oil consumption -- and ran a parallel analysis using that biomarker instead of the dietary questionnaire. Both analyses pointed in the same direction, which strengthens the case that the association reflects a true dietary effect rather than measurement error.

How It Was Designed

The basics: 7,625 participants in the main dietary analysis, 1,245 in the secondary biomarker analysis, median follow-up of 5.25 years, three French cities. Participants were aged 65 and older at recruitment, with no history of stroke at baseline.

Olive oil consumption was assessed at baseline using a structured dietary questionnaire and classified into three categories: no use, moderate use (olive oil for cooking OR dressing), and intensive use (olive oil for both cooking AND dressing). This categorization captures the practical reality of olive oil consumption in elderly populations -- people tend to either use it broadly across their cooking or not at all -- and avoids the measurement noise of trying to estimate gram-per-day intake from a brief questionnaire.

Cox proportional-hazards models were adjusted for age, sex, study center, education, income, BMI, physical activity, smoking, alcohol intake, history of hypertension, history of hypercholesterolemia, diabetes, depressive symptoms, and dietary intake of fruits, vegetables, fish, and other fats. The biomarker analysis adjusted for the same covariates plus laboratory batch.

Stroke events were ascertained through self-report at follow-up, medical record review, and hospital discharge data, then validated by an independent expert committee using standard clinical and imaging criteria. Strokes were classified by type (ischemic, hemorrhagic, undetermined) where possible.

What They Found

During a median 5.25-year follow-up, 148 incident strokes occurred in the main sample, and 27 in the biomarker sample. The multivariable-adjusted hazard ratios were:

Exposure	Hazard Ratio (95% CI)	Risk Reduction	What It Measures
Intensive olive oil use	0.59 (0.37-0.94)	41% lower	Stroke incidence, intensive vs. never users
Moderate olive oil use	~0.83 (p for trend = 0.02)	17% lower (trend)	Stroke incidence, moderate vs. never users
Top tertile plasma oleic acid	0.27 (0.08-0.90)	73% lower	Stroke incidence, biomarker analysis

Green indicates a favorable direction vs. never users / lowest tertile. Both the dietary and biomarker analyses showed significant inverse trends, with the strongest single estimate emerging in the biomarker subgroup.

Reading the Results

The findings group into three threads.

Intensive olive oil use (41% lower stroke risk). The headline result. Intensive use -- defined as olive oil for both cooking and dressing -- captures people whose diet is structurally built around olive oil rather than people who use it occasionally. The 41% reduction is large for any single dietary exposure in an elderly population. The lower bound of the confidence interval (HR 0.94) just excludes 1.0, meaning the result is statistically significant but the precise effect size could plausibly be anywhere from a modest 6% reduction to a substantial 63% reduction.

Dose-response (p for trend = 0.02). The graded effect across never, moderate, and intensive use is the kind of finding that's hardest to attribute to confounding. If olive oil intake were just a marker of an overall healthy lifestyle, we'd expect a binary effect (any use vs. none) rather than a graded one. The fact that intensive users do better than moderate users, who do better than never-users, points toward a true dose-response.

Biomarker confirmation (73% lower in the top tertile of plasma oleic acid). This is the most important methodological feature of the study. Plasma oleic acid is an objective biological measure of olive oil intake -- it doesn't depend on the participant remembering or accurately reporting what they ate. The fact that the biomarker analysis points in the same direction as the dietary analysis, with an even larger effect estimate, strengthens the causal interpretation. The wide confidence interval (0.08-0.90) reflects the small subsample size (1,245 participants, 27 events), but the lower bound still excludes 1.0.

What Didn't Change

The study could not differentiate strongly between ischemic and hemorrhagic stroke subtypes because of small numbers within each category. The overall stroke association was driven primarily by ischemic strokes (the dominant subtype in elderly French populations), but the analysis was underpowered to test whether olive oil affects hemorrhagic stroke risk differently.

The study is observational, not interventional. It cannot prove that olive oil use causes lower stroke risk. The covariate adjustment is extensive but not exhaustive -- residual confounding by overall diet quality, socioeconomic factors, or unmeasured health behaviors remains possible. The biomarker confirmation reduces but does not eliminate this concern.

Broader Context

The Three-City stroke finding sits in the same range as other olive oil cardiovascular cohort signals. PREDIMED (Spain, randomized) showed a 30% reduction in major cardiovascular events including stroke with a Mediterranean diet supplemented with extra virgin olive oil. EPIC-Spain reported a 44% reduction in cardiovascular mortality in the highest quartile of olive oil intake. The Harvard pooled cohort showed a 19% reduction in cardiovascular mortality and a 29% reduction in neurodegenerative mortality in a non-Mediterranean U.S. population.

The 2011 European Food Safety Authority opinion (Regulation 432/2012) authorized a health claim for olive oil polyphenols and protection of blood lipids from oxidative damage at a daily intake of 5 mg of hydroxytyrosol and its derivatives. Stroke prevention is mechanistically linked to oxidative stress and endothelial inflammation -- pathways where olive oil polyphenols are well-documented to act -- but the Three-City Study didn't measure polyphenol intake directly. Its biomarker (oleic acid) is a marker of monounsaturated fat intake rather than polyphenol intake specifically.

What this cohort adds is the strongest stroke-specific signal in the olive oil literature, with rare biomarker confirmation in an elderly French population.

Related Research

Continue exploring olive oil and polyphenol science:

• Nurses' Health: Mediterranean Diet & 29% Lower Heart Disease Risk in 74,886 Women
• Olive Oil and 19% Lower Mortality in 92,383 U.S. Adults Over 28 Years
• Olive Oil and Stroke Risk: A 101,460-Person Meta-Analysis

Source: View the original study on PubMed

Olivea's Dosage

The Three-City Study did not specify a gram-per-day threshold; the benefit emerged in adults who used olive oil for both cooking and dressing -- a structural pattern rather than a precise dose. A single tablespoon of Olivea extra virgin olive oil delivers approximately 14 grams. Each Olivea capsule delivers over 20 mg of hydroxytyrosol per serving in an EVOO matrix; our most recent third-party certificate of analysis confirmed 23.5 mg per capsule.

We share this research for transparency. This is an independent study -- we did not fund it, design it, or conduct it.

Editorial Information

Research note. This article summarizes third-party research published in a peer-reviewed journal. Olivea did not conduct or fund the study. Findings reflect the cited paper only and do not establish efficacy of Olivea products.

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