Brewing tea removes heavy metals from water, study finds | Science

The medicinal effect of a cup of tea is no surprise to anybody who has headed straight to the kettle after a laborious work meeting.

But researchers say they may have found a more scientific explanation for why it is associated with health benefits.

Scientists at Northwestern University in the US have found the brew removes charged atoms, or ions, of heavy metals from water.

Benjamin Shindel, the first author of the research, said that while scientists might consider whether the flavour chemicals in tea were driving associated health benefits, the new study suggested an alternative.

“I think the one possible better explanation might be that it’s because it’s removing metals from water,” he said, adding the team found a cup of black tea brewed for five minutes reduced the concentration of lead ions in water by about 15%.

While the team did not test the possible ramifications for health, Shindel said that even in a country such as the UK, where lead levels in drinking water are unlikely to be high, there could be a small effect.

“It’s possible that on the margins, tea consumption is reducing [people’s] metal intake by a very small amount, and perhaps over the population of the UK, that’s reducing diseases associated with metal consumption by another commensurately very small amount,” he said.

Among other studies, previous research has suggested people who drink tea may have a lower risk of stroke, dementia and even death.

Writing in the journal ACS Food Science & Technology, Shindel and colleagues reported how they brewed tea with different batches of water containing known concentrations of heavy metal ions. They then checked the concentration of these ions after different periods of steeping, using solutions without tea as controls.

Working with black tea, they found the brew reduced the concentration of all the metal ions tested, including lead, chromium and cadmium.

They then focused on lead, finding longer brewing times of black tea and higher temperatures of water were associated with a greater reduction in the concentration of lead ions. What is more, ground tea had a greater effect than whole leaves.

The team also found that, at least for the batches they tested, black, green and white teas reduced the concentration of lead ions in the water to a greater degree than camomile, rooibos and oolong teas when left to steep for 24 hours to reach equilibrium.

In the case of bagged tea, the materials also mattered, with empty cellulose bags found to reduce the concentration of lead ions, whereas empty cotton and nylon bags did not.

Prof Michelle Francl of Bryn Mawr College in the US and the author of Steeped: The Chemistry of Tea, who was not involved in the work, said: “If you are concerned about heavy metals in your water, don’t think that drinking tea is the solution.”

However, she added that the study “suggests some interesting directions” for developing sustainable and accessible ways to “removing contaminants from water, a critical need in many parts of the world”.