A surprising health benefit of drinking tea

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Tea has long been among the most popular beverages in the world. People drink tea in the morning with breakfast, in between meals for an afternoon caffeine hit and to relax before bed. Most research on tea has focused on the effects of caffeine, tea’s nutritional value or how it compares with coffee, but now scientists say that the stimulating beverage may provide a surprising health benefit: Your morning cup of tea could be removing dangerous contaminants from your water.

A new study published in ACS Food Science & Technology, found that tea leaves naturally adsorb heavy metals, filtering out harmful water contaminants like lead, cadmium or arsenic. The metals become trapped on the surface of the tea leaves and can be removed by simply filtering out the leaves or tossing the tea bag. (Adsorb means to cause a substance to cling to its surface, as opposed to absorb, where the substance is taken in.)

“You’re taking the metals out of the water with the tea, but you don’t consume the tea leaves after, which is why it works,” said Benjamin Shindel, the study’s lead author, who at the time of the research was a PhD student at Northwestern University in Evanston, Illinois. As tea leaves release flavorful chemicals in the water, creating a tasty drink, they are just as effective at grabbing metals out of the water, Shindel said.

Shindel’s study adds to a small body of research showing that tea adsorbs metals. A study published in November also found that tea leaves removed heavy metals from water. Saddam Husain Dhobi, the lead author of that study, said this research highlights the value of tea and “its potential as a safe and effective method for mitigating harmful substances.”

In the new study, researchers experimented with a variety of teas, brewing methods and steeping times, and they examined the difference between loose-leaf and bagged tea.

And the recipe for the purest cup of tea depends on one major factor: time. The longer the steep time, the more metal that’s removed.

For example, researchers found that when steeping an average cup of tea for five minutes, there was a 15 percent reduction in lead concentrations – and that trend was consistent across cups, whether the concentrations of lead were higher or lower. Brewing tea overnight, a common method for brewing iced tea, provides better water purification than steeping for a few minutes. But even a few minutes can result in a moderate removal of metals, Shindel said.

Researchers also examined different varieties of tea to determine whether they provided any extra benefits. Black and green bagged tea were tested, as were whole tea leaves, including green, oolong, white and black teas. Herbal teas were also tested for their ability to get metals to stick to the surface of the leaves.

Most teas, including herbal teas, performed similarly – apart from chamomile flowers, which adsorbed metals poorly. The study found that ground tea leaves perform best, compared with whole leaves, because grinding the leaves creates additional surface area for attracting the contaminants.

The type of tea bag mattered too. Cellulose tea bags, a biodegradable and organic material derived from trees, were highly effective at sponging metals from water. Nylon tea bags, which can release billions of microplastics, did not perform well in the study, and cotton tea bags showed trivial adsorption capabilities.

Even so, the relative benefits of different tea bags and tea types were “marginal compared to the benefit of having more time,” Shindel said.

While Shindel, who now works with the Energy Department’s National Energy Technology Laboratory, can’t definitively say what the human health outcome would be for drinking tea, he suggested that it could lead to declines in illnesses closely correlated to heavy metal exposure.

“People should be aware of the potential that preparing tea has to adsorb a fraction of the metals and potentially other contaminants from drinking water,” he said.

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