Microplastics and their even tinier cousins, nanoplastics, are probably flowing through your blood and building up in your organs like the lungs and liver.

Now, a new study is connecting the dots on microplastics' mysterious correlation with heart attack and stroke risk.

"There are some microplastics in normal, healthy arteries," Dr. Ross Clark, a University of New Mexico medical researcher who led the study, told Business Insider before he presented his findings at the meeting of the American Heart Association in Baltimore on Tuesday.

"But the amount that's there when they become diseased – and become diseased with symptoms – is really, really different," Clark said.

Clark and his team measured microplastics and nanoplastics in the dangerous, fatty plaque that can build up in arteries, block blood flow, and cause strokes or heart attacks.

Compared to the walls of healthy plaque-free arteries, plaque buildup had 16 times more plastic – just in the people who didn't have symptoms. In people who had experienced stroke, mini-stroke, or vision loss, the plaque had 51 times more plastic.

"Wow and not good," Jaime Ross, a neuroscientist at the University of Rhode Island who was not involved in the study but has studied microplastics in mice, told BI after reading the results.

"It's very shocking to see 51 times higher," she said, adding that in her research, a signal that's just three times stronger is "very robust and striking."

What exactly the plastics are doing in there, if anything, remains a mystery. The new study offers some possible clues, though.

This research has not yet undergone the scrutiny of peer review, but Clark said he plans to submit it for publication in a peer-reviewed scientific journal later this year, after replicating some of their results.

Genetic activity looked different with plastic

Clark is a vascular surgeon, not a microplastics specialist. However, he got the idea for this study by talking with his colleague Matthew Campen, who recently discovered that human brains contain a spoon's worth of plastic.