Green tea health claims questionable: ECG and EGCG cause oxidative stress, study finds

28 Oct 2021 --- Green tea is commonly viewed as healthy, and its consumption is often linked to a longer life, supposedly due to its high level of antioxidants. However, excessive consumption of green tea extracts or concentrates may cause organ damage as these cause oxidative stress. This is according to a study conducted by researchers at ETH Zurich, Switzerland.

Producer of natural green tea leaf matcha powder, Taiyo International also commented on the study findings.

“Exceeding reasonable levels of green tea extracts always comes with a risk that should not be taken by formulators or recommending health care practitioners,” Dr. Derek Timm, technical sales director at Taiyo International, tells NutritionInsight.

“At a certain concentration, green tea extracts become toxic,” says Michael Ristow, study leader and professor of energy metabolism at the Department of Health Sciences and Technology, ETH Zurich.

The study shows that the polyphenols from green tea – Epigallocatechin and Epigallocatechin gallate (ECG and EGCG) – initially increase oxidative stress in the short term, but that this has the subsequent effect of increasing the defensive capabilities of the cells and the organism.

“That means green tea polyphenols, or catechins, aren’t in fact antioxidants, but rather pro-oxidants that improve the organism’s ability to defend itself, similar to a vaccination,” Ristow explains.

This study adds more data to the effects of green tea extracts but should not detract from the wealth of literature on the health benefits and safety of green tea catechins on human and animal health, comments Timm.

“In a broader sense, the easiest way to mitigate any potential risks of green tea supplement consumption is by formulating supplements at beneficial levels confirmed in human clinical trials with minimal side effects,” he continues.

Damage to organs
The study found that high-dose catechins inhibit mitochondria so that cell death ensues, which can be particularly dangerous in the liver. Consuming these polyphenols in excessive doses may damage organs.

Ristow says he drinks green tea every day. However, he advises against consuming green tea extracts or concentrates.Green tea has long been known to have health benefits as it contains catechins called ECG and EGCG that are said to prolong life.

While most catechins are found in Japanese varieties of green tea, other green teas also contain sufficient amounts of these polyphenols.

On the other hand, black tea contains a much lower level of catechins since the fermentation process primarily destroys them.

Health claims and catechins
ECG and EGCG belong to the group of polyphenols and are considered antioxidants. Therefore, they counteract or prevent oxidative stress in the body caused by aggressive free radicals of oxygen. Previously, researchers assumed that the catechins neutralize these free radicals and thus prevent damage to cells or DNA.

ETH researchers examined how catechins act in the nematode worm C. elegans. In conclusion, they found that rather than suppressing oxidative stress, the catechins in green tea promote it. As a result, the catechins in green tea led to longer life and greater fitness in nematodes fed to them.

The increase in defensive capability manifests not through the immune system but rather by activating genes that produce certain enzymes such as superoxide dismutase and catalase. It is these enzymes that inactivate the free radicals in the nematode; they are essentially endogenous antioxidants.

Previous research showed that sport promotes health because sporting activities increase oxidative stress in the short term, thus improving the body’s defenses.

Consuming fewer calories has the same effect, as has been shown several times in animals. Mice fed a reduced-calorie diet live longer than those fed a normal, high-calorie diet.

“Therefore, it made sense to me that the catechins in green tea would work similarly,” explains Ristow.At high concentrations, green tea extracts can become toxic and cause damage to the liver.

Ristow adds that the findings from this study translate well to humans. The primary biochemical processes by which organisms neutralize oxygen free radicals are conserved in evolutionary history and are present in everything from unicellular yeast to humans.

Industry responds: Risky green tea supplements?
The best way to understand the pros or cons of green tea is by studying it extensively for a wide range of outcomes, notes Timm.

“The recent study examined the metabolic outcomes of EGCG and EGC using a C. elegans model on longevity and stress resistance. This study found EGCG and EGC significantly increased the lifespan by about 3% of the nematodes,” he adds.

Despite the claims that it may be harmful to health, “the green tea market remains strong with steady growth,” adds Timm.

Green tea holds potential
NutritionInsight previously reported on the multifunctional green tea extract. Earlier this year, green tea was supported by research that found it is beneficial for enhancing immunity and aiding cognition, cardiovascular health and digestion. In a separate study, green tea was shown to suppress food allergies.

In September, Lief Raws partnered with CellFlo6 to release a performance green tea extract called CellFlo6 that supports muscle recovery and weight management.

Meanwhile, Ito En and Taiyo International recently collaborated to bring matcha to North America’s F&B and supplement industry.

By Nicole Kerr