We eat microplastics daily, but their effect on our health was a mystery — until now

Microscopic pieces of plastic are lodged in nearly every bite of food you eat, breath of air you take and ocean you swim in. It’s estimated we ingest enough microplastics each week to equal the weight of a credit card.

Like all other things, what goes in must go out. But the effects these plastics have while in our bodies are poorly understood. No studies to date have examined their effects in people in a controlled study; only experiments done in animals or human cells in laboratory dishes are available.

Now, a new study has found that microplastics can latch onto the outer membranes — protective envelopes cells live in — of our red blood cells and stretch them out so much that it may affect their ability to transport oxygen throughout the body.

The discovery surprised researchers because cell membranes, particularly those of red and white blood cells, are known for their flexibility; they must morph into different shapes as they pass through narrow blood vessels to do their job.

Yet, microplastics’ ability to stretch cells out in turn tightens them, hampering their shape-shifting powers by destabilizing them.

Although the study was confined to cells in a lab dish, the researchers say their experiment suggests microplastics may have this effect on several other types of human cells or organs.

The research was published Tuesday in the journal PNAS.

“The possible toxicity of microplastics in human cells is currently being discussed. A priori, microplastics are not fatal immediately after ingestion into living organisms. However, it is increasingly recognized that microplastics can oxidize or stress cells through biological processes,” study co-author Jean-Baptiste Fleury of the University of Saarland in Germany, said in a statement. “The possibility that they may also stress a cell membrane through purely physical processes, however, is completely ignored by the vast majority of studies.”

While the effects microplastics have on our health are not well understood, scientists have grouped their potential consequences in two categories: physical and chemical.

Microplastics are typically less than five millimeters across — about one-third as long as an aspirin — but they can come in all shapes and sizes. Yet, it’s unclear how plastic’s physical properties can affect a person’s health.

Plastics are also slathered with chemicals, many of which are toxic, that give it qualities such as colors, transparency, added durability and resistance to temperature changes, bacteria and light radiation.

Some chemicals, including BPA, phthalates and some flame retardants, have been shown to be endocrine disruptors, meaning they affect the release of hormones in the body. These disruptors have been associated with breast cancer, reproductive problems, asthma, diabetes and obesity.