Nurses' Health: Mediterranean Diet & 29% Lower Heart Disease Risk in 74,886 Women

This 2009 prospective cohort analysis of 74,886 women in the Nurses' Health Study, published in Circulation, tested whether closer adherence to a Mediterranean dietary pattern -- a diet built around olive oil, vegetables, fruits, legumes, whole grains, and fish -- was associated with lower incidence of coronary heart disease and stroke over 20 years of follow-up. According to PubMed (DOI), women in the highest Mediterranean Diet Score quintile had a 29% lower risk of coronary heart disease and 39% lower cardiovascular mortality compared to those in the lowest quintile.

Why This Study Matters

By 2009, the evidence linking Mediterranean dietary patterns to lower coronary heart disease was reasonably well established in Mediterranean populations. What remained uncertain was whether the same pattern would protect women in a country that did not eat a Mediterranean diet to begin with. American dietary patterns differ substantially from Greek or Italian patterns, and the open question was whether partial adherence to a Mediterranean style -- adding olive oil, eating more produce, eating more fish -- would still measurably reduce cardiovascular events.

The Nurses' Health Study was the right population to answer that question. Established in 1976, it had recruited 121,700 female registered nurses aged 30 to 55 and maintained four-year-interval dietary follow-up through validated food frequency questionnaires. For the cardiovascular analysis, the researchers excluded participants with baseline cardiovascular disease or diabetes and analyzed 74,886 women over 20 years, with 2,391 incident coronary heart disease cases, 1,763 incident strokes, and 1,077 cardiovascular deaths.

The findings established that even partial adherence to a Mediterranean pattern in a U.S. population produces measurable cardiovascular risk reduction. The 2009 analysis is now one of the foundational citations for Mediterranean-diet guidance outside the Mediterranean.

How It Was Designed

The researchers used the Alternate Mediterranean Diet Score (aMed), a nine-component scoring system adapted from the original Trichopoulou score for use in non-Mediterranean populations. The score assigns one point each for higher-than-median intake of vegetables, legumes, fruits, nuts, whole grains, and fish; one point for higher-than-median ratio of monounsaturated to saturated fat (a proxy for olive oil use); one point for moderate alcohol intake; and one point for lower-than-median red and processed meat intake.

Dietary intake was assessed by validated semi-quantitative food frequency questionnaires administered six times between 1984 and 2002 -- not just at baseline. The cumulative averaged intake approach reduces measurement error and aligns the exposure variable more closely with long-term biology.

Cox proportional-hazards models estimated relative risks for incident coronary heart disease, stroke, and cardiovascular mortality across quintiles of the aMed score, adjusted for age, smoking, body mass index, physical activity, postmenopausal hormone use, alcohol intake, total energy intake, and other established cardiovascular risk factors. The 20 years of follow-up provided 2,391 incident coronary heart disease cases and 1,763 incident stroke cases for analysis.

What They Found

Comparing the top to bottom quintiles of Alternate Mediterranean Diet Score adherence, the pooled relative risks were:

Outcome	Relative Risk (95% CI)	Risk Reduction	What It Measures
Incident coronary heart disease	0.71 (0.62-0.82)	29% lower	New CHD events over 20 years
Incident stroke	0.87 (0.73-1.02)	13% lower	New stroke events over 20 years
Cardiovascular mortality	0.61 (0.49-0.76)	39% lower	Death from CHD and stroke combined

Green indicates a favorable direction vs. lowest adherence quintile. The CHD and cardiovascular mortality reductions were strongly significant (p for trend < 0.0001); the stroke association reached significance for trend (p = 0.03) despite the upper 95% CI crossing 1.0 at the quintile-comparison level.

Reading the Results

The three outcomes group around shared biology but show different effect magnitudes worth understanding.

Coronary heart disease (29% lower). The largest and most statistically robust signal in the study. Mediterranean adherence reduced new coronary events by nearly a third in this population. The plausible mechanisms include the well-established effects of olive oil polyphenols on oxidized LDL and endothelial function, the favorable lipid profile shifts from monounsaturated-fat-rich oils replacing saturated fats, and the cumulative effect of higher polyphenol, fiber, and omega-3 intake from the broader pattern.

Cardiovascular mortality (39% lower). The largest single effect in the study. This composite outcome captures fatal coronary events and fatal strokes together. The 39% reduction reflects both the lower incidence of new events in the higher-adherence group and likely better survival from the events that did occur. Confidence interval (0.49-0.76) is tight enough to support the magnitude.

Stroke (13% lower). A smaller and less statistically robust signal. The quintile comparison crossed 1.0 in its upper confidence bound, but the dose-response trend across quintiles reached significance (p = 0.03). This is consistent with the broader literature in which Mediterranean diets show clearer effects on coronary disease than on stroke, possibly because stroke etiology is more heterogeneous (hemorrhagic, ischemic, lacunar) than coronary disease, with different risk-factor profiles.

What Didn't Change

This is an observational cohort, not a randomized trial. It cannot prove causation. The 27 covariates adjusted for include the major established cardiovascular risk factors, but residual confounding by health-conscious behavior patterns is not eliminated. Women who score higher on the Alternate Mediterranean Diet Score may also exercise more, smoke less, and have better access to medical care -- factors that contribute to their lower event rates beyond the diet itself.

The study also does not isolate olive oil specifically. The aMed score uses the monounsaturated-to-saturated fat ratio as a proxy for olive oil consumption, which captures the broader pattern of healthy fat intake but cannot separate olive oil from other monounsaturated-rich foods.

Broader Context

This analysis was published four years before the original PREDIMED trial (2013, republished 2018 in NEJM), which demonstrated a 30% reduction in major cardiovascular events with a Mediterranean diet supplemented with extra virgin olive oil in a randomized Spanish trial. The Fung 2009 Nurses' Health analysis provided the observational counterpart in a U.S. population. Together with the Guasch-Ferre 2022 Harvard analysis of 92,383 U.S. adults (19% lower all-cause mortality with higher olive oil intake), these studies established that Mediterranean-style eating produces measurable cardiovascular protection outside the Mediterranean.

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 5 mg of hydroxytyrosol and derivatives per day. The Nurses' Health analysis did not measure polyphenol intake directly, but the monounsaturated-fat-ratio component of the aMed score reflects the same dietary pattern that would supply that polyphenol dose.

Related Research

Continue exploring olive oil and polyphenol science:

• Olive Oil and Stroke Risk: A 101,460-Person Meta-Analysis
• Three-City Study: Intensive Olive Oil Use Linked to 41% Lower Stroke Risk
• Olive Oil and 19% Lower Mortality in 92,383 U.S. Adults Over 28 Years

Source: View the original study on PubMed

Olivea's Dosage

This study used a dietary pattern score rather than a specific olive oil dose. The Mediterranean pattern it scored is consistent with daily olive oil intake of about one tablespoon or more. A single tablespoon of Olivea extra virgin olive oil delivers approximately 14 grams. Each Olivea capsule delivers over 20 mg of hydroxytyrosol per serving, well above the 5 mg/day EFSA threshold; 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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