The Effects of Microplastics on Your Health & How to Reduce Them

The episode opens by presenting microplastics as a topic of broad relevance because they are found almost everywhere: in the air, in beverages, in the linings of soup cans and in paper cups made to hold hot water, coffee and tea. The host says there is a substantial body of animal data, and some human data, indicating that these particles of varying sizes can be harmful to health. He immediately sets a boundary on that claim.

we don't have any causal data linking microplastics to specific human diseases.

Because of that gap, the episode presents itself as a review of correlative data together with practical steps to limit exposure or help remove microplastics from the body. The host says microplastics are already present in essentially every organ and tissue and that exposure is constant. He also says he does not want to be alarmist, and that the goal is to explain what microplastics are, where they occur in particularly high amounts and what people can do, not to produce fear or "hypochondriasis." He argues that the Earth will not be rid of microplastics because they are too pervasive. He makes one exception to his measured tone: people who are pregnant, people with young children, and young children themselves should "really strive to limit their exposure."

The host returns to this balance more than once. The body is "incredibly good at dealing with foreign invaders," he says, but microplastics and nanoplastics have been shown to lodge in specific tissues and stay there for long periods. He warns that the episode will alternate between alarming findings and reassurance that it is not yet clear how worried people should be. His stated aim is to present the evidence so listeners can decide how much effort to put into limiting exposure and clearing these particles from their bodies.

the data just don't line up with one argument or the other, that they're extremely dangerous or that they're nothing to worry about.

Microplastics are defined in the episode as plastic particles from one micron (1/1000 of a millimeter) up to five millimeters in diameter. Particles smaller than one micron are classed as nanoplastics. Both are described as abundant in air, in the ocean, in food (especially packaged food), in cup linings and in "everything that we consume, essentially." The stated concern is that these particles could disrupt cellular and organ health and could potentially lead to certain forms of disease.

To show how unsettled the field is, the host discusses a claim that has circulated in the media and on podcasts: that people ingest up to a credit card's worth of microplastics and nanoplastics every week. He acknowledges that a paper did argue this. He then cites a more recent paper that analyzed the same data with a different quantitative method. According to that reanalysis, the original estimate was too high by a millionfold, and it would take 23,000 years to ingest a credit card's worth of plastic. The host's point is less about which number is right than about the fact that two analyses of the same data can disagree this much.

Despite the uncertainty about quantities, the host says one finding is consistent: microplastics turn up wherever researchers look for them. He jokes that a PhD advisor in toxicology or environmental science looking for a "surefire publication" could send a student to find another source of microplastics. He adds that a thesis is not only about getting a publication. He reports an explosion of studies in the last couple of years examining which human tissues, not only animal tissues, contain these particles.

wherever people look for microplastics, they find them.

The first tissue the host discusses is the brain. Postmortem studies of deceased adults reportedly find microplastics making up about 0.5% of total brain weight, which he compares to about a teaspoon of salt or sugar. Later in the same passage he calls it a half teaspoon of powder. To put that amount in context, he describes neuron cell bodies, the part containing the nucleus and DNA, as ranging from about five to eight microns across up to 50 or even 100 microns depending on location in the nervous system. Against that scale, he argues, this quantity of plastic could be spread across many places in the brain.

The host separates what he finds concerning from claims he rejects. He notes that others have argued microplastics and nanoplastics may correlate with autism or attention deficit hyperactivity disorder, and says explicitly that he is not making that argument.

I don't actually believe that the data there are strong enough to make those arguments at all.

His concern rests on a narrower inference. Postmortem studies quantify microplastics in different brain compartments, and the particles are reported to be lodged in particular categories of neurons involved in reward, motivation and movement. Because neural function is precise, he argues, it is plausible that the particles could affect how the nervous system works. He then qualifies this: "there's no direct causal relationship, at least not in humans," though there are interesting animal data that he says the episode will return to.

The host frames brain findings in terms of the blood-brain barrier (BBB). He explains that most brain tissue is not replaced across the lifespan. New neurons are produced in only a few places, such as the olfactory bulb and the dentate gyrus of the hippocampus, and people are born with far more neurons than they have when they die. He describes the BBB as a barrier designed to keep molecules that might be dangerous out of the brain. Microplastics and nanoplastics are getting from the bloodstream into the brain, and that is what he means by saying they cross the BBB.

He notes that many substances enter the blood and that this is not necessarily harmful if the body can excrete them, for example through liver detoxification. The concern is that particles reach tissues the body guards with especially strict barriers. He names the blood-testicular barrier in males, which protects germ cells and their DNA so that mutations are not passed to offspring, and the blood-follicle barrier in females, which protects the source of eggs. The host says microplastics and nanoplastics cross both barriers. He cites press coverage from the past year reporting microplastics and nanoplastics in every human testicle analyzed from postmortem tissue.

Beyond these protected organs, the host says microplastics and nanoplastics have been found in all other tissues examined. He says he knows of no investigation of human or animal tissue that failed to find them. Specific sites he lists include the upper and lower lungs, which indicates deposition deep in the lungs, the bloodstream from blood draws, and the liver.

The host traces the problem to the period after the 1950s, saying little plastic was in use before then. He illustrates this with the line "the future is plastics" from the film "The Graduate," spoken to Dustin Hoffman's character as he lies in a pool after graduating. He also mentions, as an aside, the film's scene of a drive across the Bay Bridge. Materials such as polyethylene and polyurethane were developed for durability and longevity. He stresses that they are not biodegradable, break down poorly if at all, and certainly do not break down within biological tissues. Plastics went from essentially nonexistent in the 1940s to being part of nearly all manufacturing, including aspects of surgical implants.