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Accumulations of microplastics and nanoplastics (MNPs) in the brain rose from 2016 to 2024 and were found in higher levels in the brain than in other organs, new research suggested.

In a trial that examined postmortem tissue, concentrations of MNPs were significantly higher in brain samples from 2024 than in those from 2016. Investigators also found that MNP levels were 7-30 times greater in the brain than in the liver or kidney.

Clinical implications of the findings remain unclear, and investigators urged caution when interpreting the results as it is not yet known whether MNPs actually cause any health effects.

In fact, clinicians “should not be encouraging people to undergo any dramatic change of lifestyle to avoid plastics because you want to preserve health and the best guidance for whatever issue is at hand,” senior investigator Matthew J. Campen, PhD, regents’ professor, Pharmaceutical Sciences, The University of New Mexico, Albuquerque, New Mexico, told Medscape Medical News. “We really need to reinvest time and effort to understanding the pathway of these nanoplastics getting into our bodies.”

The findings were published online on February 3 in Nature Medicine.

MNP Hijackers

MNPs can range in diameter from 1 nm (1 billionth of a meter) to 500 μm (1 millionth of a meter).

The investigators used pyrolysis gas chromatography-mass spectrometry plus visualization methods to assess accumulation of MNPs in samples from bodies that underwent autopsies in 2016 and in 2024.

The 28 brain samples from 2016 were similar in demographics (mean age at death, 45 years; 10 women) to the 24 brain samples from 2024 (mean age at death, 51 years; 10 women). The causes of death for the 2016 vs 2024 samples were violence/trauma (9 vs 9, respectively), substance use (12 vs 2), and natural disease (7 vs 13).

Results showed that although the liver and kidney samples from 2024 had similar median concentrations of particles (433 and 404 ug/g, respectively), the concentrations were much greater in the brain samples (4917 ug/g, P < .0001). Of note, the brain samples were all from the frontal cortex.

“We think the liver and kidneys are doing their job, as organs that clear waste from the body. On the other hand, the brain has limited clearance mechanisms,” co-first author Marcus Garcia, PharmD, PhRMA Foundation Fellow, The University of New Mexico, said at a press briefing.

Compared with 2016 samples, those taken in 2024 showed higher accumulations of MNPs in the brain (P = .01) and liver (P = .001).

Campen noted that most of the plastic particles found are thought to be “in the nano-scale range,” with the length appearing to be < 200 nm, or “roughly the size of two COVID viruses side-by-side,” he said.

Although the study did not explore how the plastics may be crossing the blood-brain barrier, “we postulate that nanoplastics are hijacking their way into the body, along with dietary fats. We do not think [MNPs] are floating freely in the blood but are packaged in the circulating fats,” Campen said.

Association With Dementia?

Interestingly, the accumulation of MNPs in the brain was even greater in samples from a cohort of 12 individuals with a documented diagnosis of dementia than in samples from those with no dementia. Investigators were quick to note that the findings show an association and not causation.

“We saw three to five times the concentrations in dementia patient samples, which is a little bit alarming,” Campen noted. However, “we want to be very cautious in interpreting these results as the microplastics are very likely elevated because of the disease. And we do not currently suggest that microplastics could cause the disease,” he added.

When examining 12 different polymers, the researchers found greater concentrations of polyethylene — the most commonly used plastic — in 2016 brain samples vs 2024 brain samples (P = .005), and in the brain vs in the liver or kidneys (P < .0001). Polyethyline is used in product packaging, trash bags, toys, and housewares.

Age, race/ethnicity, sex, and cause of death were not significant influencers in MNP accumulation.

Investigators now want to go beyond examining just the frontal cortex, Garcia said. They were able to “isolate and collect an entire hemisphere” of the brain and want to map the entire section and see if one specific region has greater accumulation than others.

“We want to use that information to start looking at more clinical data,” Garcia said.

Contributors or ‘Merely Bystanders’?

Commenting on the study for Medscape Medical News, Phoebe Stapleton, PhD, associated professor in the Department of Pharmacology and Toxicology at the Ernest Mario School of Pharmacy at Rutgers University, Piscataway, New Jersey, cited the use of multiple techniques to identify the MNPs as a study strength.

“It was also interesting and concerning that they showed an increase in plastic deposition in tissues over a very short amount of time, especially given how little we know” about what it means, said Stapleton, who was not involved with the research.

The discovery of greater accumulation in the brain than in the kidney and liver was also surprising, Stapleton said.

“The theory for most physiologists is that if you’re looking for [MNPs], then they would be in those filter organs and not in the brain, which is thought to be better protected,” she said. “I don’t know if it’s that they’re getting into the brain and can’t get back out because of the blood-brain barrier. That’s where more research is going to be needed.”

Data about the dementia samples “should be taken with a grain of salt,” Stapleton noted. “We don’t know if the micro and nanoplastics are playing a role in the dementia disease, or if the dementia disease is changing the blood-brain barrier to allow more [MNPs] to come in.”

In a statement from the UK nonprofit Science Media Centre, Antonis Myridakis, PhD, lecturer in environmental sciences, Brunel University of London, London, England, noted that the study algins with recent findings that MNPs are present in the blood and major organs.

“The discovery of MPs in cerebrovascular walls and immune cells adds new insight into their potential role in neuroinflammation and warrants further investigation,” Myridakis said.

However, he too, noted that it is too early to draw conclusions about direct health risks. 

“Further research is needed to determine whether [MNPs] actively contribute to neurological disorders or if they are merely bystanders in an increasingly plastic-polluted environment,” he said.

This study was funded by the National Institutes of Health. The investigators, Stapleton, and Myridakis reported no relevant financial relationships.