Could a Cup of Green Tea a Day Keep the Flu Bug Away?

Green tea has become increasingly popular in cafés and restaurants not just as a culinary ingredient but also as a contributor to healthy well-being. Green tea, derived from the plant Camellia sinensis, has been an important custom in Japanese culture long before receiving attention from the global market and general public. International exposure has led to an increase in demand and distribution from Japan to its Asian neighbours and other countries, delivered in drinks, confectionery, and its basic powder form. Green tea has not only gained popularity amongst culinary enthusiasts who praise the tea product for its aroma and taste, but it has also attracted health professionals who are curious of the health benefits it has claimed to yield.

The health benefits that have been associated with green tea vary from inhibiting negative effects of food poisoning and allergies to lowering risk of obesity and hypertension ¹. In the field of medical microbiology, green tea has been reported to contain compounds that interfere with viral activity, preventing viral diseases from developing and causing further harm to the human body.

One of the most common viral diseases that remains prevalent today is influenza, commonly known as the flu. The influenza virus is known for its high mutation rate which allows it to infect a variety of species. Throughout the years there have been outbreaks in the human population which originated from human contact with animals, such as birds and pigs. Symptoms associated with the flu include sore throats, headaches, and fatigue. According to Dr Hiroshi Yamada from the University of Shizuoka, Japan, some Asian cultures believed tea prevents the common cold, a similar acute illness. Thus, research was conducted to apply this belief to green tea and determine how tea serves as a potential remedy against influenza.

After studying green tea at a biochemical level, a particular compound from C. sinensis was discovered to be capable of suppressing the influenza virus and its associated symptoms. Known as a catechin, the compound was found to exhibit characteristics that demonstrated antiviral activity. Catechins are also active against other pathogens in the respiratory tract, which is a common infection site for influenza ². They directly prevent infection by binding to glycoprotein spikes on the surface of viruses. This action renders the virus incapable of adsorption or binding to the receptors of host cells in the respiratory tract by destroying the protective mucus coating that lines it, therefore, deterring infection ³.

The most prominent catechin compound is epigallocatechin-3-gallate (EGCG), which was the main focus of Mikio Nakayama’s research against influenza viruses. Nakayama found that EGCG could inhibit agglutination (clumping effects) in two types of viruses, including Influenza A (the main cause of flu epidemics). This prevents them from successfully attaching to host cells. Other catechins, such as Epigallocatechin (EGC) and Epicatechin-3-O-gallate (ECG), were used in similar experiments and displayed some capacity for anti-viral activity, but EGCG was found to be the most effective.

Alongside understanding the biochemistry behind green tea, a few studies provide insight into the use of green tea as a protective measure against influenza within communities. Some studies examined the effects of gargling green tea in the elderly population, while others concentrated on its health benefits in children and high school students. In one study, gargling green tea or its ingredients was associated with a lower likelihood of infection than gargling water or placebo alternatives ⁴. In another study, 124 elderly volunteers who gargled catechin extract exhibited similar therapeutic effects, while 200 healthcare workers in a separate investigation demonstrated the same outcome and were protected against the Influenza A virus. Thus, it is evident that EGCG and other tea catechins have been associated with protection against the influenza virus in humans.

Despite the potential application of tea catechins in antiviral protection, existing evidence does not verify green tea as an alternative to medical treatments. Annual vaccinations remain a viable defence option against the flu bug considering the high viral mutation rates that lead to re-emerging outbreaks of influenza and related pandemics, such as the 2009 Swine Flu outbreak.

The prospect of using green tea as an effective prevention tool requires further investigation to determine its effectiveness. In 2014, Yamada’s team published findings focused on a cohort of 757 high school students gargling bottled green tea from the Kakegawa Tea Merchants Association. They detected little to no difference in protection against infection between those who gargled with green tea and those with water ⁵. These findings, however, were restricted by limitations like motivation amongst high school participants and their exposure to environmental risk factors involved with infection. Further assessments on a larger-scale, not limited to children and elderly citizens, are necessary to paint a bigger picture and to deliver clear evidence on whether catechins are beneficial as a means to protect against viral infection within the general population. Additional research would be required if consumers were to drink green tea during the flu season and companies were to decide whether beverages and tea extract supplements are credible investments.

Tea drinking has been celebrated for generations with its rich history and signature taste. The biochemical properties of green tea have played roles, with varying degrees of success, in deterring and protecting the human population from infectious illnesses like influenza. To be served as what Tomita describes as a ‘functional food beverage’, scientists and healthcare professionals will have to persist in their endeavours to understand how efficient catechins operate in antiviral protection against a disease that poses a dangerous threat, especially as it continues to evolve ⁶. So can a cup of green tea truly keep the flu bug away? As with all medical research, only time will tell.

This article was specialist edited by Kym Bain and copy-edited by Gemma Donnelly.

1. For those interested in beneficial effects of green tea, refer to https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2855614/
2. For more information or a general review on catechins, refer to https://www.mdpi.com/1420-3049/22/8/1337
3. For a detailed understanding of the pathology and mechanics of influenza viruses, refer to https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2504709/
4. To learn more about gargling green tea and its effect on influenza prevention, refer to https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4866433/
5. To read and discuss Yamada and his team’s findings, refer to https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0096373
6. If you are interested in learning more about green tea, its history, and its potential in healthcare, refer to https://www.cabi.org/cabebooks/ebook/20173328607