Why brewing tea is good for your health 

By Stephen Beech

Brewing tea is good for your health as it purifies the water by removing toxins, reveals new research.

The brewing process removes "significant" amounts of toxic heavy metals from drinking water, scientists say.

And the longer the steeping time, the more contaminants are adsorbed.

American researchers showed that brewing tea "naturally adsorbs" heavy metals, such as lead and cadmium, effectively filtering dangerous contaminants out of drinks.

They explained that heavy metal ions stick to, or adsorb to, the surface of the tea leaves, where they stay trapped until the used tea bag is disposed of.

Study senior author Dr. Vinayak Dravid, of Northwestern University in Illinois, said: “We’re not suggesting that everyone starts using tea leaves as a water filter.

“For this study, 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.”

First author Benjamin Shindel, a former Northwestern University PhD student, said: “I’m not sure that there’s anything uniquely remarkable about tea leaves as a material.

“They have a high active surface area, which is a useful property for an adsorbent material and what makes tea leaves good at releasing flavor chemicals rapidly into your water.

"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.”

To conduct the study, published in the journal ACS Food Science & Technology, the Northwestern research team analyzed how different types of tea, tea bags and brewing methods affect heavy metal adsorption.

The varieties tested included “true” teas - such as black, green, oolong and white - as well as chamomile and rooibos teas.

The team also examined the differences between loose-leaf and commercially bagged tea.

They created water solutions with known amounts of lead and other metals and then heated the solutions to just below boiling point.

They then added the tea leaves, which steeped for varying time intervals, from a few seconds to 24 hours.

After steeping, the researchers measured how much of the metal content remained in the water.

By comparing metal levels before and after adding the tea leaves, they were able to calculate how much was effectively removed.

The researchers identified several trends after multiple experiments.

After testing different types of bags without tea inside, the researchers found cotton and nylon bags only adsorbed "trivial" amounts of the contaminants.

But the findings showed that cellulose bags worked "incredibly well."

The researchers explained that the key to a successful sorbent material is high surface area.

Similar to how a magnet attaches to a refrigerator door, metal ions cling to the surface of a material. So, the more area for the particles to stick to, the better.

Dr. Shindel believes that cellulose, which is a biodegradable natural material made from wood pulp, has higher surface area - and therefore more binding sites - than sleeker synthetic materials.

He said: “The cotton and nylon bags remove practically no heavy metals from water.

“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.”

When comparing different varieties of tea, the team found that tea type and grind played "minor" roles in adsorbing contaminants.

Finely ground tea leaves, particularly black tea leaves, adsorbed slightly more metal ions than whole leaves.

The researchers attributed that to surface area.

Dr. Shindel, who now works with the U.S. Department of Energy’s National Energy Technology Laboratory, said: “When tea leaves are processed into black tea, they wrinkle and their pores open.

“Those wrinkles and pores add more surface area.

"Grinding up the leaves also increases surface area, providing even more capacity for binding.”

Out of all the experiments, Dr. Shindel says one factor stood out most.

Steeping time played the most significant role in tea leaves’ ability to adsorb metal ions.

The longer the steeping time, the more contaminants were adsorbed.

Dr. Shindel said: “Any tea that steeps for longer or has higher surface area will effectively remediate more heavy metals.

“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.”

Although results depend on several factors, such as steeping time and water-to-tea ratio, the researchers concluded that tea preparation removes a "significant" amount of lead from water from a public health perspective.

The team estimates that tea preparation can remediate about 15% of lead from drinking water, even up to lead concentrations as high as 10 parts per million.

The estimate applies only to a “typical” cup of tea, which includes one mug of water and one bag of tea, brewed for three to five minutes.

Dr. Shindel said: “Ten parts lead per million is obviously incredibly toxic.

“But with lower concentrations of lead, tea leaves should remove a similar fraction of the metal content in the water.

"The primary limiting factor is how long you brew your tea for.”

He added: “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.

“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.”