China is the birthplace of tea and the origin of its culture. Since the creation of the first Cup of tea over 4,700 years ago, tea has become the most commonly consumed beverage globally after Water. Both ancient texts and modern medical research suggest that drinking tea is beneficial to health.
Although all teas originate from the same plant—the tea plant—different oxidation levels determine their variety. For example, Green Tea is an unfermented type, meaning it contains the richest concentration of polyphenolic compounds known as catechins, which are powerful antioxidants capable of neutralizing or preventing oxidative stress caused by oxygen free radicals in the body, thereby preventing damage to cells or DNA. As a result, green tea has anti-aging properties. However, a recent study published in Aging by researchers from the University of Jena in Germany, ETH Zurich in Switzerland, and Huazhong Agricultural University has reached a revolutionary conclusion: rather than inhibiting oxidative stress, the catechins in green tea actually promote it in the short term.
Green tea enthusiasts, don't panic just yet—let's delve into what this means.
Clinical trials and epidemiological studies have previously shown that drinking green tea is beneficial for health, including lowering Blood pressure, blood sugar, and cholesterol levels, as well as aiding weight loss. The most abundant polyphenolic compounds in green tea leaves are epigallocatechin gallate (EGCG) and epicatechin gallate (ECG), which make up 70% of the total catechin content in green tea. Experiments with various model organisms have demonstrated that green tea catechins help extend lifespan due to metabolic adaptation and enhanced resistance to reactive oxygen species (ROS).
However, the bioavailability of green tea catechins in mammals is poor, making it unlikely that human oral consumption could achieve these concentrations. Nonetheless, some independent clinical trials have confirmed that drinking green tea improves various health-related physiological indicators. After consuming 4.5 grams of decaffeinated green tea powder, the maximum plasma concentrations of EGCG, ECG, and epicatechin (EC) reached 2.5 μM in humans.
In this study, researchers tested whether a concentration of 2.5 μM was sufficient to promote longevity in the nematode Caenorhabditis elegans by inducing a mitotic response. They found that EGCG and ECG at a concentration of 2.5 μM were able to enhance the physical performance and extend the lifespan of the worms; furthermore, this relatively low dose was sufficient to inhibit mitochondrial respiratory chain activity in the worms.
Subsequent experiments with isolated mouse liver mitochondria showed that EGCG and ECG inhibited the activity of mitochondrial complex I. After six hours of EGCG exposure and twelve hours of ECG exposure, complex I was inhibited, accompanied by transient formation of ROS and a decrease in ATP.
The extension of the worms' lifespan by EGCG and ECG was dependent on the presence of the energy metabolite-activated kinase AAK-2 and the NAD-dependent protein deacetylase SIR-2.
These data indicate that the subsequent energy deficiency triggered by a transient drop in AMP activates the worms' energy sensors AAK-2 and SIR-2.1. Additionally, the temporary increase in ROS levels may promote the activity of the p38 mitogen-activated protein kinase homolog PMK-1, thus stimulating the corresponding signaling cascade.
These signaling pathways trigger adaptive responses by enhancing the activity of ROS defense enzymes superoxide dismutase (SOD) and catalase (CTL), increasing resistance to oxidative stress, and promoting health and longevity.
In summary, the inhibition of mitochondrial complex I is once again proven to be a potent tool for promoting longevity.
Professor Michael Ristow of ETH Zurich's Department of Health Sciences and Technology and the Center for Energy Metabolism, the corresponding author of the study, said, “This means that green tea catechins are not antioxidants but pro-oxidants that can stimulate the body to increase its self-protection capabilities, similar to how vaccinations work.”
Ristow is not surprised by the mechanism of action. His research team demonstrated back in 2009 that exercise promotes health by temporarily increasing oxidative stress, thereby enhancing the body's defenses. Calorie restriction has the same effect, which has been repeatedly confirmed in animal experiments. Mice fed a low-calorie diet live longer than those fed a normal high-calorie diet.
Ristow explained, “So the catechins in green tea would also work in a similar way, which makes sense to me.”
He believes that the results of this study apply to humans as well. The fundamental biochemical processes for neutralizing oxygen free radicals are conserved throughout evolutionary history, present in everything from single-celled yeast to humans.
Ristow drinks green tea every day himself but advises against taking green tea extracts or concentrates. He said, “At certain concentrations, they become toxic. High doses of catechins can inhibit mitochondria, leading to cell death, which is particularly dangerous in the liver. Anyone who consumes excessive amounts of these polyphenols risks organ damage.”
Produced by the Chinese Cooperative Times · Tea Weekly Full Media
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