What are the health benefits of green tea?

According to a report from the International Institute of Sustainable Development, tea is the second most consumed beverage in the world, after water.

All tea types, except herbal, are brewed from the dried leaves of the Camellia sinensis bush. The level of oxidation of the leaves determines the type of tea.

Green tea is made from unoxidized leaves and is one of the least processed types of tea. For this reason, it contains the most antioxidants and beneficial polyphenols.

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People used green tea in traditional Chinese and Indian medicine to control bleeding and heal wounds, aid digestion, improve heart and mental health, and regulate body temperature.

Studies suggest that green tea may have positive effects on weight loss, liver disorders, type 2 diabetes, Alzheimer’s disease, and more.

However, it is important to note that more evidence is necessary before scientists can definitively prove these possible health benefits.

In countries where green tea consumption is high, some cancer rates tend to be lower. However, human studies have not shown consistent evidence to prove that drinking green tea reduces the overall risk of cancer.

A 2020 database review of epidemiological and experimental studies in humans produced inconsistent results as well as limited evidence of the benefit of green tea consumption for lowering the risk of cancer. The researchers assessed 142 completed studies, including 1.1 million participants.

However, the topical application of green tea polyphenol extracts may have a role in protecting the skin from UVB radiation. A 2018 review of in vitro, in vivo, and human studies demonstrated the potential benefits of tea polyphenols in the chemoprevention of UVB-induced skin cancer.

Animal and test tube cell studies have suggested some positive impacts on the following types of cancer:

• breast
• bladder
• ovarian
• colorectal (bowel)
• esophageal (throat)
• lung
• prostate
• skin
• stomach

Overall findings from numerous human studies have yielded inconsistent results and limited evidence of the benefit of drinking green tea on the overall risk of cancer.

A review of several studies found that the catechins in green tea and caffeine may have a role in increasing energy metabolism, which may lead to weight loss.

A further meta-analysis of several different tea polyphenols-induced weight loss mechanisms suggested that catechins and caffeine synergistically produced weight loss effects, as opposed to them being the result of caffeine alone.

However, the impact of drinking green tea on weight loss is unlikely to be of clinical importance. Most studies that have shown small changes in metabolism used green tea extracts with extremely high concentrations of catechins.

Learn more about how green tea can help with weight loss here.

Green tea has anti-inflammatory properties. A review of human clinical studies and both cellular and animal experiments found that green tea and its major component, epigallocatechin-3-gallate (EGCG), have demonstrable anti-inflammatory effects.

A 2019 analysis of tea extract use in cosmetics supported this. The researchers determined that solutions including tea extracts promoted anti-inflammatory responses when applied topically. They also found that skin microcirculation improved in the affected areas.

A 2006 study suggested that green tea consumption is associated with reduced mortality due to cardiovascular disease.

The study followed over 40,000 Japanese participants aged 40–79 for 11 years, starting in 1994. It found that the participants who drank at least five cups of green tea per day had a reduced risk of mortality due to cardiovascular disease.

A 2016 meta-analysis of research into green tea and cardiovascular disease supported these findings. A total of nine studies involving 259,267 individuals were included in the analysis. The researchers concluded that the consumption of green tea was associated with favorable outcomes regarding the risk of cardiovascular and ischemic related diseases.

Separate reviews from 2017 and 2019 also found that the polyphenols in green tea may lower blood pressure, decrease inflammation, and improve epithelial function, which can help reduce heart disease risk in people with excess weight or obesity.

A 2011 review found that consuming green tea, either as a beverage or in capsule form, was linked to significant but modest reductions in total low-density lipoprotein cholesterol.

Drinking green tea or coffee regularly seems to be associated with a reduced risk of stroke.

An American Heart Association (AHA) study stated that the inclusion of green tea in a person’s daily diet may be associated with a small but positive change in stroke risk.

Studies concerning the relationship between green tea and diabetes have been inconsistent.

Some have suggested a lower risk of type 2 diabetes in people who drink green tea than in those who consume no tea. One review of 17 randomized control trials found a correlation between green tea consumption and decreased fasting glucose and fasting insulin levels.

A further 2017 review of dietary polyphenol studies also associated green tea, as part of the Mediterranean-type eating pattern, with a reduced risk of type 2 diabetes.

However, other studies have found no association at all between tea consumption and diabetes.

Some research has suggested that green tea can enhance a person’s working memory and other cognitive functions.

The double-blind volunteer study found that green tea could be promising in treating cognitive impairments associated with neuropsychiatric conditions such as dementia.

A 2016 meta-analysis of observational studies suggested that daily tea drinking is associated with a decreased risk of cognitive impairment and mild cognitive impairment.

In a 2011 test tube cell study, researchers tested the effect of a component of green tea, colon-available green tea extract (CAGTE), to see how it affected a key protein in Alzheimer’s disease.

The tests used CAGTE to represent green tea phytochemicals potentially available after upper gastrointestinal digestion and differentiated PC12 cells as a model for neuron cells.

The researchers found that at high concentration levels, CAGTE was able to protect the cells from the damaging free radicals and beta-amyloid peptides that may play a role in the development of Alzheimer’s disease.

However, the concentration they used was far greater than can be found in the human body.

Other benefits

Other studies have suggested that green tea might help prevent dental cavities, stress, and chronic fatigue, treat skin conditions, and improve arthritis by reducing inflammation.

However, further human clinical trials are necessary to firm up these theories.

Unsweetened brewed green tea contains fewer than 3 calories per cup.

Green tea contains a relatively small amount of caffeine (approximately 29 milligrams [mg] per 8-ounce cup) compared with black tea (around 47 mg per cup) and coffee (about 95 mg per cup).

The caffeine in a cup of tea can vary according to the duration of infusing time and the amount of tea infused.

Green tea contains one of the highest amounts of antioxidants of any tea. Green tea is about 30% polyphenols by weight, of which approximately 80% is EGCG.

Green tea is available in many types and forms, including:

• bottled and sweetened with sugar or an artificial sweetener
• single tea bags
• loose leaf
• instant powder
• green tea supplements, in capsule form or as liquid extracts

Various green tea products are available to purchase online.

In adults, there are few known side effects associated with drinking green tea.

However, the following risks and complications are important to note:

• Caffeine sensitivity: People with severe caffeine sensitivities could experience insomnia, anxiety, irritability, nausea, or an upset stomach after drinking green tea.
• Liver damage: Consuming a high concentration of green tea extract may negatively impact liver health in rare cases.
• Other stimulants: If a person consumes green tea alongside stimulant drugs, it could increase their blood pressure and heart rate.

The majority of research has suggested that the rare cases of liver injury from green tea extract consumption are idiosyncratic reactions. Reviews of these instances have also not been able to conclude direct causality.

The Food and Drug Administration (FDA) does not regulate green tea supplements. As a result, these supplements may contain other substances that are unsafe for health or have unproven health benefits.

Always check with a doctor before starting any herb or supplement regimen.

Green tea may have a number of health benefits. For example, it may help weight management, skin inflammation, and type 2 diabetes. Some research has also linked green tea consumption to improved cardiovascular health.

Green tea has one of the highest concentrations of antioxidants of any tea. It is naturally low in calories and contains less caffeine than black tea and coffee.