Your Daily Tea Routine Is Protecting You From Heavy Metals, Study Finds

Researchers have identified another great reason to drink tea: it naturally purifies water.

Researchers from Northwestern University have found that tea leaves absorb certain harmful metals from water, such as lead and cadmium, preventing us from ingesting them. The researchers emphasize that tea leaves shouldn’t replace water filters, but their work sheds light on how this beloved drink is passively protecting our health. Their study, published Monday in the journal ACS Food Science & Technology, finally gives tea drinkers a real reason to feel superior to coffee drinkers.

“I’m not sure that there’s anything uniquely remarkable about tea leaves as a material,” Benjamin Shindel, the study’s first author and an engineer at Northwestern University, said in a university statement. “But what is special is that tea happens to be the most consumed beverage in the world. You could crush up all kinds of materials to get a similar metal-remediating effect, but that wouldn’t necessarily be practical. With tea, people don’t need to do anything extra. Just put the leaves in your water and steep them, and they naturally remove metals.”

That’s because heavy metal ions—atoms of heavy metals with an electric charge—cling to the surface of tea leaves. To investigate this property, Shindel and his colleagues measured levels of metals, including lead, chromium, copper, zinc, and cadmium, in heated solutions before and after steeping with different kinds of teas, tea bags, brewing methods, and steeping times.

Their method yielded several noteworthy observations. Perhaps unsurprisingly, the most important factor in tea’s ability to filter heavy metals is time: the longer the tea steeped, the more heavy metals it filtered from the water.

“Some people brew their tea for a matter of seconds, and they are not going to get a lot of remediation. But brewing tea for longer periods or even overnight — like iced tea — will recover most of the metal or maybe even close to all of the metal in the water,” Shindel explained.

Another important aspect is the tea leaves’ surface area. In short, the higher the surface area, the more binding sites for metal ions and the more heavy metals tea leaves can absorb. That means using ground tea leaves versus loose-leaf tea, or vice versa, does not significantly change the leaves’ metal absorption properties.

“When tea leaves are processed into [tea], they wrinkle and their pores open,” said Shindel. “Those wrinkles and pores add more surface area. Grinding up the leaves also increases surface area, providing even more capacity for binding.”

Tea bags play a role in absorbing contaminants as well. The team noted that while cotton and nylon bags barely absorbed any heavy metals, cellulose (plant-based) bags absorbed a significant amount. “Nylon tea bags are already problematic because they release microplastics, but the majority of tea bags used today are made from natural materials, such as cellulose. These may release micro-particles of cellulose, but that’s just fiber which our body can handle,” Shindel said. He also added that cellulose’s filtering ability might also be due to it potentially having a higher surface area than synthetic materials.

Overall, the researchers concluded that a typical cup of tea (one mug of water with one tea bag steeped for three to five minutes) could filter out approximately 15% of lead from the water—even if the water contains toxic levels of lead. And while the researchers emphasize that tea would not be the solution to a true drinking water crisis, their work does reveal practical insights that might impact future public health research.

“Across a population, if people drink an extra cup of tea per day, maybe over time we’d see declines in illnesses that are closely correlated with exposure to heavy metals,” Shindel said. “Or it could help explain why populations that drink more tea may have lower incidence rates of heart disease and stroke than populations that have lower tea consumption.”

In other words: tea drinkers, keep doing what you’re doing.