Microplastics, heart attacks and the scientific method
This week the European Heart Journal published a study which found that people who had suffered a serious heart attack also had higher levels of micro- and nano-plastics in their blood, compared to patients who have chronic ischemic heart disease, and those with normal blood vessels.
Given how serious that finding sounds, we sought comments from experts to help journalists to understand the story. The context the experts added revealed a key step in the chain of the scientific method, but one that can lead to overhyped stories in the media.
One of the difficult things about reporting on science is that the majority of reporters are not experts, and at times it takes an expert to tease out the nuance in a scientific paper. This is where the AusSMC’s Expert Reactions can be a reporter’s best friend, not just for quotes, but for understanding the background and the context around a study.
The research was a small study, involving analysis of the blood of 61 patients in Italy, using a method known as pyrolysis-gas chromatography-mass spectrometry to detect the presence of the chemical signatures for micro- and nano-plastics.
The team then looked to see if there appeared to be a pattern of higher, or lower, levels of these plastics that lines up with people suffering from heart attacks. As it happens, their analysis showed higher levels of plastics like polyethylene, which is found in packaging and consumer products, in the blood of people who had suffered heart attacks.
The headlines, then, might read: “Microplastics are causing heart attacks!”, but as the experts told us, although the evidence is mounting that microplastics are harmful to human health, this type of study actually doesn’t prove that. As an observational study, it can only show that there appears to be a link between higher levels of microplastics and heart attacks.
According to Dr Julia Shanks, Senior Research Fellow in Physiology at the University of Auckland: “While it is noted that this study cannot definitively say that the micro-and nano-plastics were the cause of the heart attack, it is noteworthy that, in the modern world, we are increasingly finding micro- and nano- plastics in unexpected places.”
Professor Thava Palanisami from the Australian Plastics Research and Innovation Laboratory at the University of Newcastle told the AusSMC that “while the findings do not prove that plastics directly cause heart attacks, they strengthen the growing scientific evidence that plastic pollution is an emerging public health issue deserving serious attention.”
The headline could instead read: “More evidence suggests microplastics may be contributing to heart attacks”.
The size of the study is also a limiting factor, because 61 people is relatively small when considering something that potentially impacts entire populations. Having such a small sample size makes it more likely for other things to influence the results.
It might be the case that some other factor influences heart attack risk and microplastics in this particular population in Italy that doesn’t scale up to other populations globally.
“The study highlights the need for larger, long-term human studies to determine whether reducing exposure to micro- and nano-plastics can lower the risk of cardiovascular disease,” Prof Palanisami said, while Emeritus Professor Ian Shaw from the University of Canterbury said that he would consider it “a pilot study”, given the number of patients involved.
These ‘pilot studies’ are an important step in the journey of scientific discovery, but it can get murky if they are reported in a way that makes it sound like there is a definitive finding.
Even just measuring microplastics can be difficult.
Professor Kevin Thomas from the University of Queensland, noted that the method used to detect microplastics, pyrolysis-gas chromatography-mass spectrometry, is not very good at detecting polyethylene, which was one of the main plastics detected in the study.
“It is just as plausible that endogenous lipids [fats] in the blood are being misidentified as plastics."
"The headline could just as well read 'Patients who suffer heart attacks have more lipids in their blood’,” he said.
Professor Thomas has written previously on the subject of detecting microplastics in human tissues, where he acknowledged that each current method has its own strengths and blind spots.
Speaking about that research, Professor Thomas said that one of the best ways to build confidence is to use multiple different tests on the same sample.
“When they all point to the same result, we can be far more confident we’re truly detecting plastic rather than something else,” he said.
This study, then, is not the final verdict on the impact of micro- and nano- plastic on heart attacks, but it is a great starting point for further research.
As Professor Palanisami told the AusSMC, “Overall, this study is an important step forward, but much larger prospective studies with harmonised analytical methods and detailed exposure assessment are needed before firm conclusions can be drawn about the causal role of micro- and nano- plastics in cardiovascular disease.”
You can read the full AusSMC Expert Reaction here.
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This article originally appeared in Science Deadline, a weekly newsletter from the AusSMC. You are free to republish this story, in full, with appropriate credit.
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