Green Tea: Usage, Health Benefits & Side Effects

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Tea is widely consumed all over the world; In fact, the only beverage consumed more than tea is water. The Camellia Sinensis plant, or the tea bush, yields black tea, white tea, and green tea varieties.

Green tea has been consumed for millennia in Eastern Asia as a healthy beverage. It is highly regarded by traditional Chinese healers for its health properties.

Today, green tea is popular in Europe and the USA primarily because of its purported ability to manage certain conditions. But can green tea really treat conditions like cancer and cardiovascular diseases?

In this article, we turn to scientific research on the health properties of green tea to separate facts from farce.

What is Green Tea?

Green tea is derived from the leaves of the plant Camellia Sinensis, just like black tea. The difference between the two, however, is in the production process.

The process of making black tea involves fermentation but with green tea, there is no fermentation [1]. Fermentation involves oxidation of vital tea plant chemical compounds [2].

Green tea is prepared in such a way as not to interfere with its chemical composition. It instead undergoes steaming to preserve its natural color and chemical composition [3].

Green tea is a staple in Asian countries like Japan, China, and the Koreas. It has been consumed in the region for approximately 4700 years and is used to tackle wellness issues from headaches to mood swings.

Currently, it is also the fourth most frequently consumed beverage in North America [4]. Green tea is popular in both Asia and America as a refreshing beverage and also for its health benefits.

The true value of green tea lies in its chemical composition. The most significant components relating to green tea’s health benefits are the polyphenols.

The major polyphenols in green tea are flavonoids. Green tea contains the largest amount of flavonoids compared to the other teas.

The flavonoids in green tea are composed of 80%-90% catechins. The four main catechins in green tea are:

  • Epicatechin (EC)
  • Epigallocatechin (EGC)
  • Epicatechin gallate (ECG)
  • Epigallocatechin gallate (EGCG) [5]

Other important chemical compounds in green tea include caffeine, chlorogenic acid, gallic acid, quercetin, kaempferol, and myricetin.

Note that the chemical composition of green tea is relative to climate, horticultural practices, and the position of the leaf on the harvested shoot.

Is Green Tea Safe?

Research has proven green tea to be safe for consumption[6]. Note, however, that green tea is a natural diuretic.

When taken in copious amounts it can lead to frequent urination which in turn causes dehydration and electrolyte disproportion [7]. The recommended consumption rate of green tea is three cups per day.

People who take more than five cups in a day may experience side effects like nausea, dehydration, lethargy, insomnia, dizziness, an irregular heart rate, and psychomotor agitation.

Green tea may also interfere with the absorption and effectiveness of some medications [8]. If you are on any medication, please consult your doctor before taking green tea.

Green Tea Health Benefits

Green Tea Health Benefits

Green tea has been linked to various health benefits by both its proponents and science. Here are some of these benefits.

1.    Helps Reduce the Risk of Cancer

Green tea is believed to reduce the risk of getting cancer. Population studies of places like Japan where green tea is consumed religiously reveal lower cancer rates.

What the science says:

Scientific studies suggest that indeed green tea compounds showcase some inhibitory activities against tumorigenesis in different organs. According to clinical studies, the catechin EGCG is the most ferocious in cancer prevention.

EGCG impedes the specific binding of tumor promoters to their receptors hence preventing tumors from taking hold and growing. It also works with other catechins to prevent the release of tumor necrosis alpha-factor which stimulates tumor promotion and progression in cells.

In a study where lymphoma cells were transplanted into mice, green tea was proven to have prevented 50% of the tumors from taking root. It also significantly inhibited tumor growth where the tumors took root.

In another study, a significant delay in the onset of cancer among participants was also attributed to the consumption of green tea [9].

Note, however, that the effect of green tea on specific cancers remains largely inconclusive. More research needs to be done on the effects of green tea on various cancer sites [10].

2.    Manages Cholesterol and Reduces Risk of Cardiovascular Diseases

Green tea is believed to be good for the heart because it lowers the risk of heart disease significantly. It reduces the ratio of LDL (bad fats), which are linked to cardiovascular diseases, to HDL (good fats).

The efficacy of green tea against LDL may explain the low prevalence of cardiovascular among Japanese men.

What the science says:

A study among 40,000 Japanese adults showed that green tea is inversely proportional to cardiovascular disease mortality [11]. According to this study, women who consumed more than five cups of green tea in a day reduced their risk of cardiovascular disease mortality by up to 31%

In another placebo-controlled trial, participants with mild to moderate LDL levels were given green tea extract once a day. Their LDL levels reduced by 16.4% and their total cholesterol by 11.3%.

The catechin EGCG found in green tea is potent resveratrol. Resveratrol limits the effects of fats and lipids on the cardiovascular system

However, several other pieces of research and trials into the impact of green tea on lipids, blood pressure, and specific cardiovascular diseases have been inconclusive. More research needs to be done along those lines.

3.    Helps Treat Skin Conditions

Green tea has also been associated with healthy skin. It is believed to clear acne, prevent premature aging, and protect skin from UV damage.

Some people steam their faces with green tea to hydrate the skin and detoxify their pores.

What the science says:

Green Tea is rich in polyphenols. Both human and animal research studies have shown that green tea polyphenols have UV protection capabilities [12] [13].

Green tea polyphenols also have anti-inflammatory and antimicrobial properties that target skin cells. The Polyphenols have also been proven to curb the effects of reactive oxygen species (ROS) overproduction.

Overproduction of ROS depletes physiologic ROS-scavenging enzymes that cause damage to Proteins, Lipids, and DNA. Excessive production of ROS largely increases the risk of skin disease.

Research using pooled human keratinocytes revealed that ECGC reactivates dying skin cells.

Both human and animal studies show that both topical and oral administration of green tea is effective in skin protection. The topical application of green tea does not alter the polyphenol concentration in the body system compared to oral administration.

4.    Has Antifungal Properties to Help Tackle Infections

Green tea and green tea extracts are believed to be very effective against fungal infections.

What the science says:

Polyphenols make up 35% of green tea’s dry weight. The polyphenols contain flavanols that are rich in catechins.

Various scientific studies have shown catechins to display anti-fungal properties.

In a research study aimed at testing anti-fungal capabilities, five Candida isolates were treated with green tea extracts. The research concluded that green tea has a strong and broad spectrum of antifungal activity against the Candida fungi [14].

The anti-fungal activity was credited to ECGC and EGC catechins. Studies relate to the anti-microbial properties of green tea to its catechin content [16].

5.    Has Anti-Viral Properties

Topical ointments containing green tea extracts have been approved for the treatment of HPV by the FDA [17]. Green tea is also believed to be potent against the influenza virus.

HPV is spread through either sexual activity or skin-to-skin contact with an infected person. If HPV goes untreated it can turn to cervical cancer.

What the science says:

Recent studies have shown that green tea catechins indeed have antiviral effects against various viruses.

In a study of the effects of green tea catechins on hepatitis viruses, it was found that catechins inhibit hepatitis viruses. ECGC, in particular, can create a microenvironment that inhibits HBV replication [18] [19].

In another study, EC, EGC, ECG, and ECGE also showed strong antiviral activity against the Herpes simplex virus. ECGC was shown to make the HSV virus lose its infectious ability.

ECGC and ECG catechins were also proven to inhibit the replication of several influenza virus subtypes. Subsequent research findings back up these results on the antiviral properties of green tea catechins.

6.    Helps with Weight Management

Some people believe that drinking green tea regularly can help with weight loss by increasing the body’s fat-burning capabilities. The caffeine and ECGC compounds found in green tea increase the body’s metabolism hence its ability to burn fat.

The above explains the popularity of green tea diets and the presence of green tea extract in most fat burner supplements.

What the science says:

In a study by the American Journal of Clinical Nutrition, men who were given a combination of green tea and caffeine burned more calories in comparison to those who only took caffeine or a placebo.

The study established that a combination of ECGC and a small dose of caffeine promote thermogenesis in the body. Another study, also by the American Journal of Clinical Medicine, proved the spike in thermogenesis [20].

In the second study, a green tea diet was shown to increase the body’s heat expenditure by up to 4% in a 24-hour duration. The 4% increase in heat expenditure was equated to losing 10lbs in a month.

Green tea has an inhibiting effect on insulin and prevents sugar from being converted to fats. The combination of increased metabolism and increased thermogenesis means a quicker breakdown of fats and sugars.

In another study, a group of persons with obesity was given a combination of green tea and caffeine before meals. The combination appeared to not affect avid caffeine consumers while low caffeine consumers gained some weight.

Yet another study showed that green tea that is high in catechins resulted in greater weight loss than a low catechin beverage.

While some trials back up the positive effects of green tea for weight loss and management, others are inconclusive. None of the studies demonstrate the long-term effects of green tea on weight loss [22].

Green Tea Side Effects

Green tea, being a natural herb is generally safe to take. However, if taken in excessive amounts, it can alter or hamper certain processes in the body.

Below are some of the effects of green tea and their symptoms.

  • Excess caffeine in the body system: A cup of green tea contains 30-60mg of caffeine per cup which is less than the caffeine in one cup of coffee. However, if taken in copious amounts it can lead to too much caffeine in the body. The symptoms of excessive caffeine include:
    • Insomnia
    • Restlessness
    • Tremors
    • Upset stomach
    • Nausea
  • Frequent urination: Green tea is a natural diuretic and when taken in excessive amounts will cause frequent urination. Frequent urination can cause dehydration and electrolyte imbalance as exhibited by the following symptoms.
    • Headaches
    • Lethargy
    • Irregular heart rate
    • Distress
  • Iron deficiency: The tannins in green tea may bind with iron making the iron difficult to digest. If iron is constantly not being digested, it can lead to iron deficiencies like anemia. Some of the symptoms of iron deficiency include:
    • Weakness
    • Shortness of breath
    • Irritability
    • Headaches
    • Irregular heartbeat
  • Tooth decay: The tannins in green tea may cause tooth decay.
  • Inhibit medication function: Green tea may interfere with the functioning of certain medications rendering them ineffective. Blood thinners for starters cannot be taken alongside green tea.

If you notice any of the above symptoms while on a green tea diet, please consult your doctor. Also, if you are on any medication, please consult your doctor before starting a green tea diet.

Otherwise, you will be jeopardizing your health.

Usage and Dosing Considerations

What is Green Tea

Studies show that green tea infusions are generally safe to consume. Traditional green tea infusion in particular is recommended.

One study recommends two-three cups of green tea per day but anything above five is too much. Another study, however, suggests that the key to green tea dosage is the amount of ECGC catechins consumed per day [21].

For traditional green tea infusions, consumption of 800mg ECGC/day is safe. But green tea extracts, supplements, and beverages are another matter.

The catechins in these substances differ in concentration and composition from traditional green tea infusions. The same 800mg ECGC/day for supplements and the likes have had instances of elevated serum transaminases which is indicative of toxicity or liver injury.

However, hepatotoxicity with green tea is rare and is often attributed to idiosyncratic reactions. This is particularly concerning supplements, green tea extracts, and flavored beverages.

Apart from the recommended daily dosage, there are several other factors to note regarding green tea consumption:

  • Always consider the brand of green tea because the amount of catechins, particularly EGCG, may vary from brand to brand.
  • Green tea while fasting increases the catechins in the body system to toxic levels.
  • There is insufficient information on the effects of green tea on children, adolescents under 18, pregnant women, and nursing mums. If you fall in any of these categories avoid taking green tea altogether.


When is the best time to take green tea?

There is no recommended time to enjoy a cup of green tea. It comes down to personal preferences and the power of deduction.

Green tea contains caffeine which is a stimulant so taking it before going to bed may not be the best idea. Green tea may also inhibit the absorption of certain minerals so taking it alongside meals may lead to certain nutritional deficiencies.

Can I take green tea first thing in the morning on an empty stomach?

Taking green tea under fasting conditions is not recommended. When you wake up from sleep, you have come from a state of fasting.

The answer is no. Avoid taking green tea on an empty stomach in any instance.

Is green tea bad for my kidneys?

Being a natural herb, green tea is rather safe to take. However, when taken in excess it can lead to a spike in catechin concentration in the blood. Elevated catechin levels can cause hepatotoxicity.

The excess catechins normally target the liver and can cause liver damage in very rare and extreme cases. When you take too much green tea, your liver may be at a higher risk compared to your kidneys.

How much green tea should I take to lose weight?

The research on the effects of green tea on weight loss is mostly inconclusive. Some clinical trials posit that the weight loss achieved using green tea is clinically irrelevant.

Also, note that the green tea extracts used in clinical trial research are extracted using special methods to retain higher content active ingredients. It is way more potent than regular green tea infusions you may have at home.

Given the inconsistent research results on weight loss and varying compositions of green tea extracts; there is no standard recommended daily dose for weight loss.


Green tea has been taken for thousands of years both as a beverage and for its health benefits. Modern society is turning to green tea as a natural remedy for various health conditions.

Green tea is believed to improve a host of medical conditions from weight loss to cancer. While it may work for some conditions, the research on its efficacy in tackling other conditions is inconclusive.

Do your research and consult your doctor, especially if you intend to use green tea for an existing diagnosis.

As a natural herb, green tea is quite safe to consume; probably the reason why there is no recommended standard dosage. However, moderation is key. More is never best, especially for supplements or green tea diets.

Whether for health or pleasure, there is more good than harm in a cup of green tea.


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