Green tea: Health benefits, side effects, and research

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People have hailed the health benefits of green tea for centuries. Studies suggest that consuming green tea may positively affect skin health, help with weight loss, and reduce the risk of cardiovascular disease, among other benefits.

Green tea comes from unoxidized leaves of the Camellia sinensis bush. It is one of the least processed types of tea, containing the most antioxidants and beneficial polyphenols.

Some research suggests green tea may positively affect weight loss, liver disorders, type 2 diabetes, Alzheimer&#;s disease, and more. However, more evidence is necessary for researchers to definitively prove these health benefits.

This article lists some potential health benefits and types of green tea, its nutrition content, and the potential side effects.

Cancer prevention

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

A database review of epidemiological and experimental studies in humans produced inconsistent results and limited evidence of green tea&#;s benefits for lowering cancer risk.

The researchers assessed 142 completed studies, including 1.1 million participants.

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

A review suggests green tea catechins have some positive impacts on the following types of cancer:

• breast
• colorectal
• esophageal
• lung
• prostate
• liver

Overall, more research on humans is necessary to prove the benefit of green tea on the overall risk of cancer.

Weight loss

A review suggests green tea and the catechin epigallocatechin gallate (EGCG) it contains may help people with obesity to reduce their body weight.

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 green tea and weight loss.

Inflammatory skin conditions

Green tea has anti-inflammatory properties. Research highlights the anti-inflammatory effects of green tea.

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

Lower cholesterol

A review concluded that green tea consumption can significantly lower total cholesterol and low-density lipoprotein cholesterol in people with moderate weight, overweight, or obesity.

However, the authors highlight the need for more research, particularly longer studies with more diverse populations.

Stroke risk

According to the American Heart Association (AHA), drinking large amounts of green tea without sugar may reduce the risk of stroke.

A review and meta-analysis supports this, associating moderate green tea consumption with a lower risk of stroke after evaluating five studies with 645,393 participants and 11,421 incidents of stroke.

Type 2 diabetes

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 study of people with and without diabetes in China associates daily green tea consumption with a lower risk of type 2 diabetes. It also associated daily green tea consumption with a lower risk of all-cause mortality in people with diabetes.

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

However, further research is necessary to fully determine the relationship between diabetes risk and green tea.

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Working memory

A study of 264 adults in China associates regular green tea consumption with better cognitive function, particularly executive function and memory.

Several smaller studies support this. A study suggests acute green tea extract supplementation improved working memory capacity in 10 women ages 50&#;63, although there was no significant effect for younger adults.

Similarly, another study examined the effect of green tea catechins on adults ages 50&#;69 in Japan. The authors suggest daily green tea supplementation may benefit working memory.

According to a review, certain amino acids in green tea have an anti-stress element that helps to slow brain aging.

Alzheimer&#;s disease

According to a systematic review, current research generally supports the hypothesis that green tea may reduce the risk of Alzheimer&#;s disease and dementia.

This may be due to the neuroprotective effects, including anti-inflammation and anti-oxidative stress, of certain catechins in green tea.

However, further research is necessary to strengthen this evidence.

Other benefits

Green tea may also benefit other conditions. For example, the United States Food and Drug Administration (FDA) has approved a green tea extract ointment as a prescription treatment option for genital warts.

A review suggests green tea phytochemicals may reduce skin aging.

Other research suggests green tea may have the following effects:

• prevent tooth decay and cavities
• improve osteoarthritis pain
• antiallergic effect
• promote wound healing

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

Nutritional breakdown

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, which has around 47 mg per cup, and coffee, which has 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.

Types

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

Side effects and risks

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 may increase their blood pressure and heart rate.

Most research suggests that the rare cases of liver injury from green tea extract consumption are idiosyncratic reactions. Reviews of these instances have yet 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.

Frequently asked questions

Below are some common questions about green tea.

What is the best time to drink green tea?

Further research is necessary to determine the best time to drink green tea. However, since green tea contains caffeine, some people may prefer to drink it in the morning.

What happens if a person drinks green tea every day?

Research suggests it is safe for most adults to drink up to 8 cups of unsweetened green tea daily. However, people should be aware of the amount of caffeine in the brand they choose.

Very high quantities of green tea may lead to liver damage or interact with certain medications.

Does green tea reduce belly fat?

Some research suggests that regular tea consumption, including green tea, may help to reduce body weight and waist-to-hip ratios. However, several factors can influence fat loss, including total calorie intake and exercise levels.

Summary

Green tea may have several health benefits. For example, it may help with weight management, skin inflammation, and type 2 diabetes. Some research also links 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.

Most people can drink green tea daily with no side effects. However, some people may experience sleep disturbances due to the caffeine in green tea if they drink large amounts or consume it late in the day.

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