Green Tea is made from Camellia Sinensis leaves and buds. prepared by steaming and pan-frying these leaves and then dry them. It is the healthiest beverage in the world because it is an antioxidant. what you hear about green tea benefits are all true. but you know it has side effects too? No? let's discuss.
Green tea contains caffeine just like other teas but in less amount from other teas. But it may still cause problems. It may cause stomach problems if taking it too strong or on an empty stomach (Source). Caffeine increases the acid level in the stomach which can lead to acid reflux and nausea. so to avoid stomach problems with green tea, then take it after a meal.
According to some Taiwanese studies, drinking excessive green tea can lead to iron deficiency anemia because tea interferes with iron absorption (Source 1, Source 2).
As per one study, drinking green tea after an iron-rich meal, the main compound in green tea will bind with iron and as a result, the green tea loses its ability as an antioxidant (Source).
The main compound in green tea is EGCG (Epigallocatechin Gallate), which forcibly inhibits a pro-inflammatory enzyme called myeloperoxidase. when EGCG and iron are taken after one another, the iron bounded EGCG loses its ability to inhibit myeloperoxidase and can lead to inflammation.
Green tea contains tannins just like all teas. Tannins combine with iron especially with non-heme iron, found in plant-based food such as Peas, Green vegetables, and Beans, etc, make it limited for absorption. It can reduce the absorption of iron from food by 50% or more.
Some studies say that putting lemon juice in green tea may prevent iron absorption from food or drink, but it depends on the type of food you consume.
As you know green tea contains caffeine which is contradictory to sleep, because it stimulates the nervous system and interferes with sleep. Green tea contains less amount of caffeine but can cause problems in sleeping for people sensitive to caffeine. The chemical compounds in green tea inhibit the release of hormones called melatonin, which helps in sleeping.
Consuming green tea in late times can also cause this problem. Pregnant women and lactating mothers must avoid green tea in large amounts, because it may pass through breast milk and cause insomnia in infants.
Once again due to caffeine which is present in green tea can cause mild to severe headaches (Source). Headaches can also be caused by iron deficiency (anemia). This is again from consuming green tea in excess, so for caffeine-sensitive people, they have to take green tea in less amount.
A study found that green tea can also cause the problem of feeling jittery and shaky, which they not found in decaffeinated green tea products (Source).
Aside from the headache, green tea can also cause dizziness. According to one study, humans can accept a maximum dose of green tea up to 9.9 grams per day, which is approximately equal to 24 cups of green tea. One important point in this study is that green tea extract (GTE) is listed in more than 100 over-the-counter herbal supplements and preparations, but FDA not strictly regulated green tea extract for any treatment (Source).
According to one study, polyphenols in green tea can cause oxidative stress and consuming an excessive amount of caffeine in the form of green tea can lead to nausea and vomiting (Source).
Another study says that excessive intake of green tea can cause vomiting and nausea because it contains tannins that bind with proteins in the intestine and can lead to nausea and constipation (Source). If you are a regular drinker of green tea avoid drinking more than 5 cups per day, but if you are starting now with green tea just start with 1 or 2 cups each day.
Keep in mind the amount of green tea consumption also depends on your health status. I.e. if you have a disease like diabetes or cancer, you may need to consume more than 6 cups a day. (Source 1, Source 2)
Some studies found that the normal amount of caffeine is 300 to 400 mg per day, if the amount of caffeine exceeds this limit then it can cause many problems and vomiting is one of them (Source).
According to the study, green tea is one of the herbs that contain caffeine which is the main reason that causes diarrhea (Source).
The caffeine in green tea can cause diarrhea because it stimulates your intestines to contract and release more frequently to draw in more fluids and produce laxative effects. Loose stools could be the first side effect if you are new to green and it is because of the caffeine.
Caffeine may also stimulate the motion of your bowels to move sooner than usual. If you intake green tea (containing caffeine) early in the morning, so it is the shortest excretion time and increases the transition of fluid which can lead to diarrhea, specifically if you are sensitive to caffeine.
The best time to taking green tea is later the day (afternoon) because the transit time is longer as compared to the morning.
As per one study, the caffeine in green tea can cause a bleeding disorder (Source). Caffeine in green tea lowers the level of a protein called fibrinogen, which helps in blood clotting.
Caffeine in green tea also inhibits the oxidation of fatty acids, which can cause the consistency of blood thinner. You must avoid green tea if you have a bleeding disorder.
Consumption of green tea in large amounts can lead to high blood pressure if you are suffering from heart disease. According to a study, green tea intake can increase blood pressure more than caffeine alone (Source).
Another study says that green tea might reduce the effect of medication nadolol (Corgard), which is used to treat high blood pressure (Source).
As per one study caffeine in green tea can cause an irregular heartbeat (Source). Because caffeine stimulates the heart and causes the heartbeat to speed up and even chest pain called angina. When your heartbeat is faster than normal heartbeat you will feel your heart pounding in your chest.
Excessive intake of caffeine contained green tea can lead to dizziness because it lowers the blood flow to the brain. According to a study, that usage of caffeine over 1.5 grams each day can lead to many symptoms and dizziness is one of them (Source).
As per one study, the GTE (Green tea extract) increase the duration of convulsions, tested upon the mice and rats (Source).
Some studies show that green tea interferes with certain medicines for seizures and lead to extreme convulsions (Epilepsy Source 1, Source 2). If you are taking medication for seizures than you have to avoid green tea.
Green tea caffeine is a stimulant and diuretic. As we discussed above that caffeine increases the heartbeat and blood pressure which are both harmful in pregnancy. Caffeine also increases urination and can lead to dehydration.
According to one study, green tea compound catechins inhibit the cells in the intestine from absorbing folic acid. So there is less folic acid and the baby is at a higher risk of having NTD (Neural tube defects) (Sourced from mothertobaby.org).
Researchers suggest that during pregnancy or in breastfeeding duration you have to limit your intake of caffeine to 200mg which are 1 to 2 cups.
Caffeine enters the baby's body through breast milk and can change the pattern of sleeping in the baby and keep him awake.
In some cases, a high intake of caffeine can lead to a miscarriage of a child. Caffeine is the content that the baby cannot metabolize or it takes a lot of time to use.
According to a recent study, a high amount of green tea consumption increases the risk of Type 2 Diabetes in Chinese adults both men and women. The researchers noted the dose-response relationship between the duration and amount of consumption of tea (Source).
Although many studies have shown the benefits of green tea for diabetes (like this study), some studies found that the green tea compound catechins are harmful to treating Type 2 diabetes (Source).
As per one study, green tea extract supplements have high levels of antioxidants that are harmful to our health especially lever. Green tea ingredients catechins and EGCG are strong antioxidants. So if you are taking green tea supplements for weight loss or other benefits, it means that you are taking a high dosage of antioxidants, which are linked to liver damage.
Green tea infusions contain 90 to 300 mg of antioxidants (catechins and EGCG), but many supplements contain up to 1000 mg of antioxidants. According to researchers taking more than 800 mg of antioxidants are crucial for the liver (Source).
In modern ages, green tea extract supplements are widely used for weight loss. But there are also serious side effects of the supplements and acute liver failure is one of them (study source).
Catechins may have benefits in weight loss, cancer, and heart disease, but in case of consuming it in a large amount just like in green tea, supplements can lead to liver toxicity. According to the U.S National Library of Medicine, green tea extract products are linked to liver damage.
One other study says that containing green tea extract products used for weight loss causes acute liver failure in an individual.
As per one research, the active compounds in green tea catechins and caffeine inhibit the ability of an enzyme called phosphodiesterase, which helps in bone growth and leads to osteoporosis.
Caffeine also inhibits calcium absorption and increases calcium excretion from the body through urination, so it lowers the level of calcium in bones. Excessive intake of caffeine can lead to bone disease osteoporosis.
If green tea is consumed in large amount then its compounds become the source of prooxidants and can have bad effects on bones (Source).
A review of studies found that green tea ingredient polyphenols used in the treatment of cancer and heart disease can also lead to kidney damage if it is consumed in large amounts.
Excessive intake of green tea can lead to skin allergies, commonly eczema and hives. Eczema is that type of allergy where the skin is hypersensitive while hives are red, itchy and elevated. Hives can form in the meantime but take some time to heal. Some people experience tingling on the face, tongue, lips, and throat.
In some cases when green tea is consumed in large amounts it can lead to all body allergic reaction called anaphylactic shock. This is the condition when throat swells, blood pressure levels drop, hives breakout, pain in the abdomen and the person feels dizzy and anxiety.
Some studies say that green tea is good for dental health but green tea has also side effects for teeth. According to some studies (1, 2), green tea contains tannins and are acidic, so it can stain or discolor your teeth if you drink it in excessive amount.
Another bad effect of green tea on dental health is its slowing down of calcium absorption from food and make the teeth weak.
As per one study, excessive intake of green tea can lead to lower fertility in one’s body. This study is derived from testing on embryos and larvae with small doses of green tea and as a result, they were slower to develop. Also, green tea prevents the ability to produce offspring in their bodies.
Another study says that green tea extract decrease the serum testosterone level in one's body tested upon.
The compound of green tea caffeine is known as a natural diuretic which can lead to frequent urination. Researchers suggest limiting the consumption of caffeine within 5 cups per day which makes 200 to 300 mg of caffeine per day.
All caffeinated drinks including green tea aggravate the bladder, especially when you are suffering from Urinary Tract Infection (UTI). So you must have to avoid green tea in UTI and drink a lot of water.
Caffeine consumption can lead to bladder spasms and also cause bladder control problems. Caffeine can compress the smooth muscles of the bladder and make urination difficult. As per another study, caffeinated green tea has the potential to irritate the bladder.
Hmmm…. This is a little bit complicated, as some people may notice increase anxiety levels while others may feel a decrease.
One study shows that too much caffeine consumption may increase your anxiety level. So if you are anxiety patient and suffer from panic attacks, you may need to use decaffeinated green tea instead.
But this is not the case with every patient, as green tea also contains the “l-theanine” - an amino acid that reduces anxiety.
A study shows that those students who drank green tea had lover anxiety vs those who did not.
So, the suggestion would be to use green tea in a lower amount, probably 1 or 2 cups a day. OR test the results by yourself. If you feel an increase in anxiety, you may need to use less amount or decaffeinated green tea. But if you feel lower levels of stress, which is the case with most people, you can increase the number of daily cups.
Too much consumption of green tea may also cause muscle contraction, tremor, cramp, spasm or twitching. According to a study, this is due to the caffeine in green tea.
If you have restless leg syndrome, you should limit your green tea intake. Caffeine intake may increase these symptoms (Source).
If you have Glaucoma disease, you may take some extra precautions. Because drinking green tea, which contains caffeine may increase pressure on your eyes. This starts within 30 minutes and remains up to 90 minutes.
Some research completely discourages taking caffeinated green tea for women having this disease.
However, new research shows that green tea may help reduce Glaucoma disease. The green tea catechins, helps you strengthen your eyes, and reduce the Glaucoma disease.
So, if you are a patient of glaucoma, you may need to use decaffeinated green tea, or drink less green tea as this will help you reduce your glaucoma.
Green tea contains caffeine which speeds up the nervous system while drugs that contain stimulants also speed up the nervous system. Which may cause serious problems including increased heartbeat and high blood pressure.
So whenever possible, try to avoid taking green tea with any drug that contains stimulants.
Soon I’ll write an in-depth article for green tea interaction with other medications.
There is an old saying that "Excess of everything is bad". This applies perfectly here. Green tea does not have side effects if taken in a low or moderate amount. But if you exceeded, you may find yourself in unexpected situations. Because all these side effects of green tea are due to its larger amount of consumption.
If you know something else to include in this post or future posts OR your experience or just anything else, please let me know in the comments.