Microplastics are inside your organs. Here is what the research actually shows.

YOUR HEALTH — Issue No. 21

Microplastics — What We Know, What We Don't, and What You Can Do

The research is moving fast.

Microplastics used to be thought of as an environmental problem. Ocean pollution. Coral reefs. Something happening out there — in the water, in the fish, in places far removed from daily life.

That framing is no longer accurate.

Microplastics are inside us. They have been found in human blood, in lung tissue, in the placenta, in breast milk, in arterial plaque, and most recently in human brain tissue. And recent evidence suggests the amounts found in some human tissues may be increasing over time.

This does not mean we have all the answers. The science is moving fast and the clinical implications are still being worked out. But the evidence is accumulating quickly enough that this conversation belongs in a health newsletter — plainly, honestly, and without alarm for its own sake.

Here is what the research actually shows.

What microplastics actually are

Microplastics are plastic particles smaller than five millimeters in diameter. Nanoplastics are a subset — smaller than one micrometer, smaller than many bacteria, and small enough to cross biological barriers that larger particles cannot.

They come from two sources. Primary microplastics are manufactured at small sizes — the microbeads once used in cosmetics and exfoliants, the synthetic fibers shed from polyester clothing in the wash. Secondary microplastics are the result of larger plastic items breaking down over time — water bottles, packaging, plastic bags — degrading through UV exposure, friction, and weathering into progressively smaller fragments.

Annual global emissions of microplastics to the environment are estimated at 10 to 40 million tons. They are in the air, in the water, in the soil, in the food supply, and in virtually every ecosystem on earth. Complete avoidance is not realistic. The question is what the exposure means for human health — and what can be done to reduce it.

Where they have been found in the human body

Microplastics have now been detected in human blood, lungs, placental tissue, breast milk, arterial plaque, and brain tissue.

That does not mean we yet know what they are doing in every one of those places. But it does mean the old assumption — that plastic particles simply pass through us — is no longer tenable.

A February 2025 study published in Nature Medicine examined brain, liver, and kidney tissue from autopsy samples collected in 2016 and 2024. Brain tissue contained substantially higher microplastic concentrations than liver or kidney. And concentrations were measurably higher in 2024 samples compared to 2016 — suggesting accumulation over time rather than clearance.

That finding drew significant attention in the scientific community. The clinical implications are not yet known. The accumulation finding itself is not disputed.

The cardiovascular connection — what the NEJM study showed

In March 2024, the New England Journal of Medicine published a study that drew significant attention — and deserved it.

304 patients undergoing surgery to remove arterial plaque from the neck arteries had their excised plaque analyzed for microplastics. 58% had detectable polyethylene in their carotid plaque.

The patients with microplastics in their plaque were followed for an average of 34 months. Those with detectable microplastics had approximately 4.5 times higher risk of heart attack, stroke, or death from any cause compared to those without.

That is a striking association. It is also — and I want to be precise here — an association, not proof of causation. The study could not establish whether the microplastics caused the cardiovascular events or whether people who accumulate microplastics in their arteries are simply sicker for other reasons. Letters published in the same journal raised methodological questions about potential sample contamination in the surgical environment.

The honest Plain Medicine summary: this is the strongest human-health signal from microplastics research to date. It is observational. It does not prove cause and effect. But a 4.5-fold association in a peer-reviewed NEJM study is not something to dismiss.

How we are exposed

Three primary routes.

Ingestion — through food and water. Bottled water is a significant source — one liter contains approximately 240,000 plastic particles, the vast majority nanoplastics, particles so small they can cross biological barriers that larger fragments cannot. Tap water contains far fewer. Food stored or heated in plastic containers releases additional particles directly into food.

Inhalation — through air. Indoor air carries synthetic fibers from carpets, upholstered furniture, curtains, and clothing. The lungs filter what they can. Not everything is cleared.

Skin contact — a smaller but not negligible route, particularly from synthetic clothing worn directly against the skin.

The proposed mechanism of harm

The body has no biological template for microplastics. It has never encountered them before in evolutionary history. When plastic particles deposit in tissue, the body responds the way it responds to any foreign invader — with inflammation.

That inflammatory response is the thread that connects microplastics to virtually every disease process researchers are now investigating. Chronic low-grade inflammation is the same mechanism driving atherosclerosis, neurodegenerative disease, and metabolic dysfunction — topics Plain Medicine has covered across multiple issues. Microplastics appear to amplify that process.

The specific mechanisms being studied:

Inflammation — microplastics trigger sustained inflammatory responses in tissue. Inflammatory markers were elevated in the plaque tissue of patients with detectable microplastics in the NEJM study — the same inflammatory pathways that accelerate atherosclerosis we discussed in Issues #15 and #16. The emerging neurological concern follows the same logic: chronic inflammation in brain tissue is a known driver of neurodegenerative disease. Whether microplastics contribute meaningfully to that process is an active and urgent research question.

Oxidative stress — nanoplastics generate reactive oxygen species that damage cell membranes and DNA — compounding the inflammatory damage.

Endocrine disruption — plastics contain chemical additives — plasticizers, stabilizers — that leach into surrounding tissue. Some of these chemicals, including phthalates and bisphenols, interfere with hormone signaling in ways that affect metabolism, reproduction, and neurological function.

The body is encountering a foreign substance it was never designed to handle. It gets defensive. And sustained defensiveness — chronic inflammation — is where the damage accumulates.

Is the damage already done?

This is the question most people ask — and the honest answer is that we do not know.

There is no established human detoxification mechanism for microplastics. The liver and kidneys handle some clearance — but there is no evidence that the body fully eliminates microplastics once they have accumulated in tissue. The increasing concentrations found in brain tissue between 2016 and 2024 suggest accumulation over time rather than clearance.

What we do not know is whether accumulated microplastics cause progressive harm, whether there is a threshold below which accumulation is benign, or whether reducing future exposure meaningfully reduces risk even in someone who has already accumulated particles.

These are the questions the research needs to answer.

What you can actually do

Before getting into specifics — one important framing: this is not a recommendation to throw out everything plastic in your home. Complete avoidance is not realistic. Meaningful reduction is. The goal is to reduce exposure where the evidence suggests the biggest opportunities exist.

The five highest-leverage changes:

Stop drinking from plastic bottles. A one-liter plastic bottle contains approximately 240,000 plastic particles. Switching to filtered tap water in a glass or stainless steel bottle is one of the single highest-impact changes available.

Filter your tap water. Tap water contains far fewer microplastics than bottled water — but filtering reduces exposure further. Reverse osmosis filters remove approximately 99.9% of microplastics. Pitcher filters with certified microplastic reduction remove approximately 99.5%. Look for NSF/ANSI 401 certification. If you do not have a filter yet, boiling hard tap water for five minutes then allowing it to cool and filtering through a coffee filter removes up to 90% of microplastics — a simple interim step.

Never heat food in plastic. Heat accelerates the release of microplastics from plastic containers into food. Microwave food on ceramic or glass. Let hot food cool before transferring to plastic storage containers.

Use glass or stainless steel for hot food and drinks. This includes takeout containers, travel mugs, and food storage. The hotter the contents and the longer the contact time, the greater the release.

Reduce indoor dust exposure. Vacuum with a HEPA filter — standard vacuums recirculate fine particles back into the air. Dust with a damp cloth rather than dry. Open windows when possible to clear synthetic fibers from indoor air.

Other reasonable changes: wooden cutting boards instead of plastic, loose-leaf tea instead of plastic mesh tea bags, reducing ultra-processed and heavily packaged food.

Something worth saying plainly:

The research on microplastics and human health is early. Cause and effect has not been established in humans. The clinical implications of the accumulation findings are not yet fully understood.

That is the honest answer — and it is also not the whole answer.

The evidence that microplastics are accumulating in human tissue is not disputed. The evidence that they trigger inflammatory and oxidative mechanisms in the laboratory is not disputed. The NEJM cardiovascular association is the strongest human-health signal yet published in this area.

Waiting for certainty before taking reasonable steps has a cost. The steps above are not extreme. They are practical, evidence-informed reductions in the highest-exposure sources.

I wanted to cover this topic because I believe the evidence is strong enough to warrant the conversation — even when the evidence is not yet complete.

The Member deep-dive this week covers the brain tissue findings in depth — what the Nature Medicine study actually showed, the dementia connection that is beginning to emerge, endocrine disruption mechanisms and the specific chemicals of concern, and the most current evidence on which reduction strategies have the strongest data behind them.

Next week: The microbiome — what it is, why it matters, and what the evidence actually shows about supporting it.

Plain Medicine is published for educational purposes only and does not constitute medical advice or establish a patient-provider relationship. Always consult your healthcare provider before making medical decisions.

— Kyle