Is green tea all that it’s brewed up to be?

Its benefits are reported to be many, from reducing the risk of developing Alzheimer's to improving oral health and keeping weight in check. But are we expecting too much from this humble leaf?  

Green tea from China is the oldest form of tea, with its production dating back millennia. It remains one of the most popular teas as its purported health benefits continue to be promoted, but is there any evidence to back up these claims?

AROUND the world, we consume billions of cups of tea every day. Green tea from China is the oldest form of tea, with its production dating back millennia. It remains one of the most popular teas as its purported health benefits continue to be promoted, but is there any evidence to back up these claims?

A key component of green tea is a type of polyphenol called a catechin. Polyphenols are compounds found in many plant foods, such as fruits, vegetables, herbs, spices, tea, dark chocolate, and wine. They can act as antioxidants, meaning they can neutralise harmful free radicals that would otherwise damage cells and increase the risk of conditions like cancer, diabetes, and heart disease.

The most well-known catechin in green tea is epigallocatechin gallate (EGCG), which, because of its anti-inflammatory and antioxidant effects, may be used to improve a range of health conditions.

A review in the European Journal of Clinical Nutrition (2020) suggested there is some evidence that green tea consumption is linked to a reduced risk of developing certain types of cancer, such as lung and ovarian cancer. However, while research shows a modest beneficial effect, there is no consistent evidence of the effects of green tea on the overall risk of developing cancer.

A study in the Journal of Alzheimer’s Disease (2020) showed that green tea consumption was linked with lower levels of specific markers related to Alzheimer’s disease in people without cognitive impairment.

The study was designed to determine the association between green tea consumption and biomarkers in the cerebrospinal fluid (CSF) of the neurodegenerative disease’s pathology. Frequent green tea consumption was shown to be associated with a decreased level of CSF total-tau protein, and these findings were more pronounced in individuals aged 65 years or younger.

In Alzheimer’s disease, abnormal chemical changes cause a protein called tau to stick to other tau molecules, forming threads that eventually join to form tangles inside neurons. These tau tangles block the neuron’s transport system, harming the brain’s ability to transmit messages.

The authors concluded that the findings consolidated the favourable effects of green tea on mitigating the risk of developing Alzheimer’s disease, with the constituents of green tea potentially improving abnormal tau metabolism.

They suggested that green tea’s bioactive compounds may support brain health and reduce the likelihood of neurodegenerative diseases.

Dr Catherine Conlon is a public health doctor and former director of human health and nutrition, safefood. Pic: Brian Lougheed

However, too much green tea may not be good either. A 2023 study reported that drinking too much, 13 cups or more per day (all types of tea) could increase the risk of Alzheimer’s disease. Clinical evidence on how exactly green tea affects the human brain is lacking.

A comprehensive overview of the effects of green tea on body weight, blood pressure, blood glucose, and lipids published in Nutrition, Metabolism, and Cardiovascular Diseases (2022) concluded that green tea and its bioactive constituents have beneficial effects on these.

“These compounds are, at least in part, responsible for green tea health benefits, including a decrease in cardio-metabolic risk factors,” the authors concluded. The study involved 19 reviews, 317 randomised controlled trials and almost 25,000 adults.

Some studies show that green tea may lead to increased weight loss and lower fat accumulation in the abdominal area. A 2022 study found that drinking four or more cups of green tea daily was linked with a 44% lower chance of abdominal obesity, but the effect was only significant for women.

Green tea consumption has also been linked to better oral health. It reduces inflammation, prevents bone tissue destruction that leads to bone loss, and restricts the growth of periodontal-related bacteria.

Green tea herbal mouthwash is gaining popularity because of its potential to improve gum health and prevent bad breath.

Green tea contains a high concentration of natural fluoride, which contributes to its ability to prevent dental caries. Other components present in the tea, including polyphenols, have inhibitory effects on oral bacteria that exacerbate tooth decay.

Studies show that people who drink green tea may live longer than those who don’t. Research from Japan, published in the European Journal of Epidemiology (2019) found that those who drank five cups or more of green tea per day had a lower chance of death that those drinking one cup or less.

In his book How Not to Age, Dr Michael Gregor says the apparent mortality benefit is thought to derive largely from cardiovascular protection, ‘as both green and black tea can improve arterial function within hours of ingestion’.

Green tea is touted to be one of the healthiest beverages on the planet. Evidence shows it may help support brain and heart health, weight control, healthy teeth and gums, and fresh breath. It just might also help you live longer.

• Dr Catherine Conlon is a public health doctor and former director of human health and nutrition, safefood