How Green Tea May Impact Mental Health, Cancer, COVID-19, and More
The associated health benefits of green tea have given the drink its lofty reputation and growing popularity. Today, green tea and its components can be found in a variety of tea blends, nutritional supplements, skin treatments, and even ice cream.
Green tea’s reputed health benefits are impressive. A cup of green tea can bolster immunity and provide relief for a sore throat. Its components possess antioxidant and anticarcinogenic effects and could reduce the risk of cancer. A recent research study demonstrated that consumption of green tea can help boost DNA repair.
One of green tea’s substances—epigallocatechin-3-gallate (EGCG)—is mainly responsible for the beneficial functions that green tea exhibits. EGCG may inhibit the growth of tumors, help people lose weight, fight diabetes and high blood pressure, help protect the brain, and prevent strokes. EGCG may even counteract coronavirus (CoV) infection.
Green Tea and the Brain
Green tea—Camelia sinensis is the plant from which green and black teas are derived—is widely studied for its impacts on cognitive function and dementia risk. It has been shown to reduce psychopathological symptoms, including anxiety, and improve memory and attention. Green tea can also assist brain function through the activation of working memory, a benefit observed in functional MRI scans.
Nutrients called phytochemicals give green tea its reputation as a brain and mood food. Recent research shows that green tea may maintain positive mood states and even protect against Parkinson's disease and other brain disorders. Surprisingly, EGCG can also act as a quick pick-up without affecting sleep.
A study from the University of San Francisco observed that the tea’s polyphenols—antioxidants that neutralize free radical damage—help boost dopamine. Dopamine is a neurotransmitter and hormone that plays a role in creating positive moods. It also helps with reward feedback and motivation and assists smooth muscle movement.
Another study documented that the polyphenols in green tea positively influence the metabolism of glucose, which is an overall benefit to brain and heart health.
Researchers at the University of California at San Francisco found that a polyphenol in green tea called gallotannin helped repair brain damage and prevent neuron death in stroke victims. In addition, green tea extract helped enhance connectivity from the right superior parietal lobule of the brain to the middle frontal gyrus, possibly improving task performance.
Green Tea and the Heart
Drinking green tea can lower the risk of cardiovascular disease and stroke by reducing LDL cholesterol and triglycerides. Long-term consumption of tea polyphenols called catechins may also be beneficial against high-fat, diet-induced obesity and type II diabetes. Research on Japanese adults showed that participants who drank more than five cups of green tea a day had a 26% lower risk of death from a heart attack or stroke than people who drank less than one cup a day. They also had a 16% lower risk of death from all causes.
Japanese adults who drank more than five cups of green tea a day had a 26% lower risk of death from a heart attack or stroke than people who drank less than one cup a day.
Green tea may be a promising tool for the protection of cardiovascular disorders because it may counter plaque accumulation on arterial walls, reduce the formation of blood clots, and inhibit tumor growth. It may also have antioxidative and anti-inflammatory effects, as well as beneficial effects on blood vessel function. Recent evidence exists for beneficial effects of tea constituents on heart tissue, including positive effects on heart muscle contraction and hypoxia (low oxygen level)-induced tissue injury.
Green Tea and Cancer
There are close associations between green tea consumption and a lower risk of cancer and related mortality. EGCG may play a role in inhibiting several stages of tumor development, from tumorigenesis (tumor formation) through metastasis (secondary growth or spread). In addition, EGCG is capable of reducing cancer risk by quenching free radicals and thereby preventing oxidation-induced DNA damage and mutations.
Exploring Impacts on SARS-CoV
Recent studies demonstrated that EGCG may protect against infection by diverse coronaviruses (CoVs), including potential future emerging CoVs. Research demonstrated that EGCG plays a key role in preventing human and rodent CoV infection, including co-variants of concern, in lung epithelial cells. EGCG interfered with the attachment of CoV to sugar-chain structures on cell surfaces.
EGCG shows antiviral activity against diverse DNA and RNA viruses, including herpes simplex virus type 1 (HSV-1), influenza A virus (IAV), and hepatitis C virus (HCV). Researchers documented that EGCG inhibited HCoV-OC43 infection by disrupting the binding of the virus to its receptor, angiotensin-converting enzyme 2 (ACE2).
Green Tea and Oral Health
Green tea may also play a role in oral health. It can eliminate bad-breath (halitosis) through the moderation of odor-causing sulfur components. It is also capable of causing apoptosis (cell-death) in oral cancer cells.
Caution from Regulatory Agencies
Despite the popularity of green tea and widespread belief in its health benefits, drinking excessive amounts of green tea may lead to nausea, stomach irritation, headaches or dizziness. Also, green tea’s strong antioxidants and other properties may pose problems for people suffering from anemia or blood-clotting disorders. Therefore, the properties of green tea will need further assessment in rigorous clinical trials before questions about its efficacy are answered.
It should be noted that US regulatory agencies caution that evidence of efficacy is yet inconclusive. The National Institutes of Health (NIH) says the following: "Although many studies have been done on green tea and its extracts, definite conclusions cannot yet be reached on whether green tea is helpful for most of the purposes for which it is used."
Fortunately, tea and its components are undergoing continuous research. NIH’s National Center for Complementary and Integrative Health (NCCIH) has continued to publish research on green tea and its extracts.
Green Tea Horizons
Studies have shown that cancer-prevention strategies that combine pharmaceuticals and tea components may have potential applications. For instance, EGCG administered via drug delivery systems such as lipid nano-capsules or liposome encapsulation may significantly enhance therapeutic efficacy.
Despite the current lack of consensus on what tea’s benefits are and how they are achieved, the popularity of tea is without question. Tea revenue is expected to grow by 6.9% at least through next year. People continue to love a cup of green tea and enjoy its benefits, whatever they might be.
*Dr. Tanmoy Rana is Assistant Professor at West Bengal University of Animal and Fishery Sciences, Kolkata, India. His professional interests include arsenic toxicity, molecular diagnosis and toxicology, oxidative stress, immunopathology, nanoparticles, echinococcosis, and host-microbe interactions. He conducts multidisciplinary research in life sciences and writes and edits content as well as grants.