Microplastics and Heart Disease: The NEJM Study Explained

The study: what was done and what was found

Marfella et al. (2024) recruited 304 patients undergoing carotid endarterectomy — a surgical procedure to remove atherosclerotic plaque from the carotid artery, performed in patients at high risk of stroke. Plaque tissue removed during surgery was analysed for the presence of microplastics and nanoplastics using multiple detection methods including pyrolysis gas chromatography–mass spectrometry and electron microscopy.

Microplastics or nanoplastics were detectable in the plaque of 150 patients (58.4%). The primary polymers identified were polyethylene and polyvinyl chloride (PVC). Electron microscopy images confirmed particles physically embedded within the plaque matrix, not merely surface contamination from the surgical procedure.

Patients were then followed for a median of 34 months. The primary outcome was a composite of heart attack, stroke, or death from any cause. The result: patients with detectable microplastics in their plaque had a 4.53× higher risk of the primary composite outcome compared to those without detectable plaque microplastics. This risk ratio persisted after statistical adjustment for age, sex, smoking status, diabetes, hypertension, LDL cholesterol, body mass index, and prior statin use.

Why the plaque finding matters

The physical presence of microplastics within arterial plaque has a plausible biological mechanism for harm that goes beyond simple correlation. Atherosclerotic plaques are fatty deposits that build up in artery walls over years. Plaque stability — whether a plaque remains adhered to the artery wall or ruptures — is the key determinant of whether a patient has a heart attack or stroke. Plaque rupture, not simply plaque size, is the proximate cause of most acute cardiovascular events.

Microplastic particles embedded in plaque could plausibly affect plaque stability by triggering local inflammatory responses — chronic low-grade inflammation is already a known driver of plaque instability. The Marfella study found higher levels of inflammatory markers in patients with plaque microplastics, consistent with this hypothesis. Whether plastic particles directly destabilise plaque, or whether their presence is a marker for a broader inflammatory state, is not yet established.

How do microplastics get into arterial plaque?

The pathway begins with ingestion or inhalation. Microplastics that cross the gut lining enter the bloodstream — confirmed by Leslie et al. (2022), who detected microplastics in human blood samples. Once in circulation, particles can become incorporated into the arterial wall during the atherosclerotic process: as immune cells (monocytes and macrophages) infiltrate the artery wall to engulf lipids and form the core of plaque, they may also take up plastic particles encountered in the bloodstream and carry them into the plaque matrix.

This pathway is consistent with how other non-biodegradable particles — including asbestos fibres and silica particles — are known to be carried by macrophages and deposited in tissues throughout the body.

What the study cannot tell us

The Marfella study is an observational prospective cohort study — it followed patients over time and observed outcomes, but did not randomly assign people to different exposure groups. This means it cannot establish that microplastics caused the higher rate of cardiovascular events. Several alternative interpretations must be considered:

• Patients with more severe or longer-standing atherosclerosis may accumulate more microplastics in their plaque simply because they have more plaque — and also have higher cardiovascular risk for that reason.
• People with higher microplastic exposure (from diet and lifestyle) may also have other risk-conferring behaviours that were not fully adjusted for in the analysis.
• The study population (surgical patients with significant carotid disease) is not representative of the general population, limiting direct generalisability.

The study authors acknowledged these limitations explicitly. The 4.5× risk ratio is a large effect size — large enough that confounding alone is unlikely to fully explain it — but replication in independent cohorts is needed before this finding can be considered definitive.

Context: how significant is this finding?

Publication in the New England Journal of Medicine — the world's highest-impact medical journal — reflects the peer review community's assessment that this is a methodologically sound and clinically significant finding. The effect size is large. The biological mechanism is plausible. The adjustment for confounders was thorough. This makes it the strongest human evidence to date linking microplastic exposure to a major clinical outcome.

It is, however, one study. In clinical medicine, a single observational study does not change practice guidelines — it generates hypotheses that subsequent research tests. The appropriate response is to take the finding seriously while awaiting replication, not to treat it as definitive proof of causation.

What this means for reducing exposure

Established cardiovascular risk factor management — not smoking, maintaining healthy blood pressure and cholesterol, regular physical activity, and a diet low in ultra-processed food — remains the primary evidence-based approach to reducing heart attack and stroke risk. These factors have decades of causal evidence behind them and should not be deprioritised in favour of microplastic reduction.

That said, reducing microplastic exposure has no downside, and the Marfella finding is the most serious piece of evidence yet that it may matter for long-term health. The highest-impact exposure reductions — eliminating plastic tea bags, not microwaving food in plastic, filtering drinking water — are low-cost changes that address the largest individual exposure pathways. To see where your own exposure stands relative to these pathways, take the calculator.