What are the health benefits of green tea? cancer prevention| weight loss| skin condition| heart health| cholesterol reduction| stroke risk| type 2 diabetes| memory| Alzheimer's disease| nutrition| types| side effects| general

The health benefits of green tea have been praised for centuries. Studies have shown that drinking green tea may have a positive impact on skin health, help with weight loss and reduce the risk of cardiovascular disease.

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

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

Green tea is made from unoxidised leaves and is one of the least processed teas. As a result, it contains the highest amount of antioxidants and beneficial polyphenols.

Health benefits

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

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

It is important to note, however, that more evidence is needed before scientists can definitively prove these possible health benefits.

Cancer prevention

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

A 2020 database reviewing epidemiological and experimental studies of humans from credible sources produced inconsistent results and limited evidence of the benefits of green tea consumption on reducing cancer risk. Researchers evaluated 142 completed studies, including 1.1 million participants.

However, topical application of green tea polyphenol extracts may have a protective effect on the skin against UVB radiation. A 2018 review of credible-source in vitro, in vivo and human studies demonstrated the potential benefits of tea polyphenols in the chemoprevention of UVB-induced skin cancer.

Animal and in vitro cell studies of credible sources have suggested some positive effects on the following types of cancers：

• Chest
• Bladder
• Ovarian
• Colorectal (intestine)
• Esophagus (larynx)
• Lungs
• Prostate
• Skin
• Stomach

The overall results of many human studies have produced inconsistent results and limited evidence to suggest that drinking green tea is beneficial for overall cancer risk.

Weight loss

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

Further meta-analyses of several different tea polyphenol-induced weight loss mechanisms from credible sources suggested that catechins and caffeine synergistically produced weight loss effects, rather than caffeine alone.

However, the effects of green tea consumption on weight loss are unlikely to be clinically significant. Most studies that have shown small changes in metabolism have used green tea extracts containing very high concentrations of catechins.

Inflammatory skin diseases

Green tea has anti-inflammatory properties. A review of human clinical studies from credible sources in both cellular and animal studies found significant anti-inflammatory effects of green tea and its major component epigallocatechin-3-gallate (EGCG).

A 2019 analysis of the use of credible-source tea extracts in cosmetics supports this. The researchers determined that solutions including tea extracts promote an anti-inflammatory response when applied topically. They also found improved microcirculation in the affected areas of the skin.

Heart health

A 2006 study from a credible source showed that green tea consumption was associated with a reduction in mortality due to cardiovascular disease.

The study followed over 40,000 Japanese participants aged 40 to 79 years for 11 years, starting in 1994. The results found that participants who drank at least 5 cups of green tea a day had a reduced risk of death from cardiovascular disease.

These findings were supported by a 2016 meta-analysis of studies on green tea and cardiovascular disease. A total of nine studies involving 259,267 people were included in the analysis. Researchers concluded that green tea consumption was associated with favourable outcomes for cardiovascular and ischaemia-related disease risk.

Putting the review in context with the 2017 Trusted Sources and 2019 Trusted Sources also found that polyphenols in green tea can lower blood pressure, reduce inflammation and improve epithelial function, which can help reduce the risk of heart disease in people who are overweight or obese.

Lower cholesterol

A 2011 review of credible sources found that drinking green tea, either as a beverage or in capsule form, was associated with a significant but moderate reduction in total LDL cholesterol.

Stroke risk

Regular consumption of green tea or coffee appears to be associated with a reduced risk of stroke.

A credible source from the American Heart Association (AHA) study suggests that adding green tea to a person's daily diet may be associated with a small but positive change in stroke risk.

Type 2 diabetes

Research on the relationship between green tea and diabetes has been inconsistent.

Some believe that green tea drinkers have a lower risk of developing type 2 diabetes than non-tea drinkers. A review of 17 randomised controlled trials from credible sources found a correlation between green tea consumption and lower fasting blood glucose and fasting insulin levels.

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

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

Working memory

Some studies have shown that green tea can enhance working memory and other cognitive functions in people.

This double-blind volunteer study found that green tea may have promise for treating cognitive impairment associated with neuropsychiatric disorders such as dementia.

A 2016 meta-analysis of observational studies from credible sources suggests that daily tea consumption is associated with a reduced risk of cognitive impairment and mild cognitive impairment.

Alzheimer's disease

In a 2011 test-tube cell study of credible sources, researchers tested the effects of a component of green tea, colon available green tea extract (CAGTE), to understand how it affects a key protein in Alzheimer's disease.

These tests used CAGTE to represent the green tea phytochemicals that may be available after digestion in the upper gastrointestinal tract and used differentiated PC12 cells as a model for neuronal cells.

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

However, the concentrations they used were much higher than those found in humans.

Other benefits

Other studies suggest that green tea may help prevent tooth decay, stress and chronic fatigue, treat skin conditions and improve arthritis by reducing inflammation.

However, further human clinical trials are needed to confirm these theories.

Nutrient breakdown

Unsweetened brewed green tea contains less than 3 calories per cup from credible sources.

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

The amount of caffeine in a cup of tea will vary depending on the length of time the tea is brewed and the amount of tea brewed.

Green tea contains one of the highest levels of antioxidants of any tea. Green tea is about 30% credible source of polyphenols (by weight), of which about 80% is EGCG.

Green Tea Types

Green tea is available in a variety of types and forms, including

• Bottled and sweetened with sugar or artificial sweeteners
• Individual tea bags
• loose leaf
• Instant powder
• Green tea supplements, in capsule form or liquid extract

Side effects and risks

There are few known side effects associated with the consumption of green tea in adults.

However, the following risks and complications need to be noted:

• Caffeine sensitivity: People with severe caffeine sensitivity may experience insomnia, anxiety, irritability, nausea or stomach upset after consuming green tea.
• Liver damage: In rare cases, consumption of high levels of green tea extract may have a negative impact on liver health.
• Other stimulants: If a person takes green tea along with stimulants, it may increase blood pressure and heart rate.

Most of these studies credible sources have shown that the rare cases of liver damage caused by the consumption of green tea extracts are idiosyncratic reactions. A review of these instances also fails to conclude a direct cause-and-effect relationship.

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

Always consult your doctor before starting any herbal or supplement regimen.

In Summary

Green tea may have many health benefits. For example, it may help with weight management, skin inflammation and type 2 diabetes. Some studies have 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.

Keywords: health benefits| cancer prevention| weight loss| skin condition| heart health| cholesterol reduction| stroke risk| type 2 diabetes| memory| Alzheimer's disease| nutrition| types| side effects| general