微塑料是否对人体有害？

A new study examines possible harm caused by microscopic pieces of plastic that end up inside people's bodies.

These materials – known as microplastics and nanoplastics – can enter the body through the air or in food or drinks.

Tiny plastic pieces have received widespread attention in the media. But so far, very little research has been done on how the substances affect human heart health.

One new study suggests the buildup of such plastics inside the body can increase the risk of a stroke, heart attack or death. But the researchers noted the evidence presented cannot prove a direct link between tiny plastic materials and heart problems.

What did the study find?

The study involved 257 people who had medical operations to clear blocked blood vessels in their necks. Italian researchers examined the fatty buildup the doctors removed from the carotid arteries, which supply blood and oxygen to the brain.

Using two methods, they found evidence of plastics – mostly nanoplastics that cannot be seen – in the artery plaque of 150 patients. No evidence of plastics was seen in 107 patients.

The team followed these people for three years. During that time, 30 individuals, or 20 percent of the group with plastics, had a heart attack, stroke, or died from any cause. These rates dropped to about eight percent among those with no evidence of plastics.

Research results were recently published in a study in the New England Journal of Medicine.

The researchers also found more evidence of inflammation in individuals with tiny plastic bits in their blood. Inflammation is the body's reaction to injury and is thought to raise the risk of heart attacks and strokes.

What are the problems with the study?

The researchers admitted their study was very small. For example, it only looked at people with narrowed arteries who were already at risk for heart attacks and stroke.

And the patients with the plastics had more heart disease, diabetes and high cholesterol than those without plastics. They were also more likely to be men and more likely to be smokers. Both of those groups generally have higher rates of heart disease.

The researchers tried to account for these risk differences. But they noted they may have missed some important elements that could change the results. The team said because of these ongoing questions, this kind of study cannot prove the plastics caused the health problems.

Steve Nissen is a heart expert at the Cleveland Clinic in the state of Ohio who was not part of the study. He told the Associated Press he thinks the team's estimate that the risk of heart attack, stroke or death was four times greater seems too high.

"It would mean that these microplastics are the most important cause of coronary heart disease yet discovered. And I just don't think that's likely to be right," Nissen said.

What is next for the researchers?

Philip Landrigan of Boston College University told the AP that more research is needed on the issue. Landrigan, who wrote about the study in the Journal, said it is the first one suggesting a connection between microplastics and nanoplastics with disease in humans. Other scientists have found plastic bits in the lungs, liver, blood, placenta and breast milk.

"It does not prove cause and effect, but it suggests cause and effect," Landrigan said. "And it needs urgently to be either replicated or disproven by other studies done by other investigators in other populations."

The Cleveland Clinic's Nissen added about the study, "It's a wake-up call that perhaps we need to take the problem of microplastics more seriously. As a cause for heart disease? Not proven. As a potential cause? Yes, maybe," Nissen said.

I'm Bryan Lynn.

The Associated Press reported this story. Bryan Lynn adapted the report for VOA Learning English.

_____________________________________________

artery – n. a tube in the body that carries blood from your heart

inflammation – n. the swelling of tissue in the body

cholesterol – n. a kind of substance in the body that is linked to heart disease

contaminate – v. to make something dirty or poisonous

placenta –n. a temporary organ that forms in the womb and that provide blood and nutrition to the fetus through the umbilical cord

replicate – v. to make or do something again in exactly the same way

potential – adj. possible