Brewing tea could help to remove toxic heavy metals, including lead, from drinking water, a new study has revealed.
A good cup of tea has long been associated with numerous slight health benefits, but previous studies have tended to focus on the effects of chemicals in the tea leaves that are released during brewing.
Now, a new study has revealed that the brewing process removes charged atoms (called ions) from heavy metals in water, seemingly by chemically bonding with them. This, in turn, makes the heavy metals stick to the tea leaves, pulling them from the water. The study was published Monday (Feb. 24) in the journal ACS Food and Science Technology.
“We’re not suggesting that everyone starts using tea leaves as a water filter,” co-author Vinayak Dravid, a professor of materials science at Northwestern University, said in a statement. “Our goal was to measure tea’s ability to adsorb heavy metals. By quantifying this effect, our work highlights the unrecognized potential for tea consumption to passively contribute to reduced heavy metal exposure in populations worldwide.”
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More than 5 billion cups of tea are drunk each day, making it second only to water as the most consumed drink on the planet. Scientists have long studied the health impacts of green and black teas, and the brew has been tied to lower risks of cancer, stroke, and death due to cardiovascular disease.
But exactly why a cup of English breakfast confers these benefits is unclear. Past research linked these benefits to the chemicals released in the plants, but the researchers behind the new study suspected it could also be something to do with the brewing process itself. (Heavy metals have been tied to increased risk of stroke and cardiovascular disease.)
To investigate their hypothesis, the scientists purchased a number of teas, from the popular Lipton and Infusion brands, that include black tea, green tea, chamomile tea, oolong tea, white peony tea and rooibos tea. (Chamomile and rooibos are steeped and drunk as tea but come from a different family of plants than traditional teas.)
By brewing their teas in the same manner as regular drinkers do, the researchers tested the teas’ ability to neutralize heavy metal ions in waters of varying concentrations by comparing them to water-based mixtures without tea.
Their results revealed that a typical cup of tea — one mug of water and one teabag, brewed for three to five minutes — can remove roughly 15% of lead from water with lead concentrations up to 10 parts per million. While there is no safe level for lead in public drinking water, the Environmental Protection Agency sets the actionable limit at 15 parts per billion. Brewing reduced other metal ions too, including chromium and cadmium.
Other trends also appeared. The type of tea bag made a big difference, with cotton and nylon bags adsorbing barely any contaminants and cellulose bags removing the most. Additionally, the tea type and how finely it was ground also played a role, with finely ground black tea leaves being the best performers. These, alongside green and white teas, reduced lead ion concentrations to a greater degree than oolong, rooibos and camomile teas.
But the most significant factor was the steeping time. Perhaps predictably, teas left to brew the longest removed the most contaminants.
“Any tea that steeps for longer or has higher surface area will effectively remediate more heavy metals,” first-author Benjamin Shindel, a materials scientist at Northwestern University, said in the statement. “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.”
However, despite the promise of their findings, the researchers say that they do come with caveats. Firstly, in areas of the world with good water systems it’s unlikely that metal concentrations will reach high enough levels for teas to confer any enormous benefits. And secondly, if there is a water contamination crisis, tea will not solve the problem on its own.
But that’s not to say that drinking more tea might not be a good idea anyway.
“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.”
