7 harmful side effects of excessive consumption of green tea

Research and blogs talk a lot about the health benefits of green tea. It’s rich in antioxidants and flavonoids, which have positive influences on our physical and mental well-being. Some studies show that green tea can boost metabolism, reduce inflammation and improve cognitive function. 

But what’s less talked about are the side effects of green tea. They may be uncommon, but that doesn’t mean they don’t deserve discussion! This is of particular importance to those who have caffeine sensitivity or who may be taking certain medications which interact with caffeine and other bioactive components in green tea.

So before you brew yourself a cup, read on about the potential side effects of drinking green tea so you’re fully educated about what you’re consuming.

Nutritional facts about green tea

Since green tea as a beverage is mostly water, it actually contains 0 kCal! That’s because it doesn’t have any fat, cholesterol, carbohydrates, or proteins. It does contain small amounts of calcium, phosphorus, potassium, zinc – and of course, caffeine. [1]

A 16oz (473ml) serving of plain green tea contains 56.8mg of caffeine, which is less than the 94mg in black coffee and the 181.4mg in coffee. [2]

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Benefits of green tea

There are several health benefits to consuming green tea regularly – between 2 and 5 cups every day, to be precise. Green tea has a high concentration of polyphenols called flavonoids, which have antioxidative, anti-inflammatory and anti-carcinogenic properties. [3]

Antioxidants are components that counteract oxidative stress, which comes from free radicals. These free radicals can damage our body’s cells, which can lead to different degenerative conditions related to ageing. Antioxidants neutralise free radicals in our body and boost our longevity. [4]

Additionally, the polyphenols in green tea have an association with protection from UVB radiation, which can prevent UVB-related skin cancer. [5]

Other benefits of drinking green tea include decreased risk of cardiovascular diseases, lower LDL cholesterol levels and a boost to metabolism.

Antioxidants are components that counteract oxidative stress, which comes from free radicals

Potential side effects of green tea

Side effects are more limited when consuming green tea versus other beverages that contain caffeine, since green tea contains less caffeine and has a shorter brewing time. However, increased caffeine sensitivity or certain prescriptions can lead to some adverse reactions when consuming green tea.

#1 – Symptoms of anxiety

For those who are particularly sensitive to caffeine or consume large amounts of green tea (over 5 cups a day), you may experience symptoms of anxiety. These include tremors, shortness of breath, irritability and other manifestations. [6]

Caffeine also elevates heart rate and blood pressure, which can cause dizziness. [7]

#2 – Insomnia

Again, if you’re sensitive to caffeine, consuming large amounts of green tea may lead to sleep issues. Bioactive compounds in green tea prevent your body from releasing hormones such as melatonin, which trigger your body to wind down and ready itself for sleep.

This means that if you have difficulty sleeping or if you suffer from sleep disorders, you should avoid consuming more than a few cups of green tea a day. [8] This is especially true for matcha, which has a higher concentration of caffeine than plain brewed green tea. 

#3 – Teeth stains

Tea has a higher chance of staining your teeth than coffee due to its higher tannin content. [9] Tannins are water-soluble polyphenols present in many plant-based foods and drinks – including wine, coffee and tea. Darker teas are more susceptible to staining your teeth, but even green tea can eventually cause discolouration! [10]

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#4 – Liver conditions

The European Food Safety Authority previously assessed the effects of the catechins in green tea on the human body, particularly the liver. Some reports emerged from Nordic countries that associated the use of green tea products with initial symptoms of liver damage.

Green tea infusions (such as brewed tea) contain safe levels of epigallocatechin 3-gallate (EGCG), which is a catechin found in tea leaves. However, green tea extracts and supplements may contain at least 800mg per dose, which has associations with symptoms of negative effects on the liver. Further studies are required for validation, but the risk is present. [11]

#5 – Drug interactions

Persons who take certain prescriptions such as nadolol or polypeptide antibiotics should be mindful when consuming green tea due to potential negative interactions. The catechins in green tea may inhibit the uptake of nadolol in the digestive system and significantly reduce its effects on systolic blood pressure. [12]

Meanwhile, for patients taking substrates of polypeptides, such as antibiotics, you should exercise caution when consuming green tea. EGCG may potentially inhibit the effects of quetiapine, sunitinib and clozapine; meanwhile, it may increase the effects of diltiazem, verapamil and nicardipine. [13]

#6 – Stomach irritation

If you consume strong brews of green tea or consume it on an empty stomach, the beverage may cause stomach irritation. Tannins increase the acid in your stomach, which can lead to digestive conditions such as acid reflux or nausea. Caffeine also has a laxative effect, which may lead to diarrhoea. [14]

The EGCG polyphenol may also cause gastrointestinal toxicity when consumed in high doses, though this is mostly due to the consumption of concentrated green tea extract. [15]

#7 – Anaemia and other deficiencies in iron

The consumption of tea can interfere with the way your body absorbs and processes iron. This means that excessive consumption of green tea can lead to iron-deficiency anaemia – although this means drinking more than a litre of green tea a day. [16]

Consuming green tea for your health

There’s no denying the benefits that green tea has on your health – it’s rich in antioxidants and anti-inflammatory compounds, which positively influence your well-being and longevity. But as with many foods and drinks, it’s essential you consume green tea in moderation so that you don’t trigger any of its potential side effects.

This is especially important to consider if you have a sensitivity to caffeine, suffer from iron deficiency, or take certain prescriptions. People with hypertension should also be cautious when consuming green tea since the caffeine elevates their heart rate.

But so long as you keep it within 2–5 cups – or less than a litre – per day and follow proper brewing instructions, green tea is a wise and healthy addition to any diet!

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[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6412948/
[2] https://fdc.nal.usda.gov/fdc-app.html#/food-details/171911/nutrients
[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5465813/
[4] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3614697/
[5] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5774988/
[6] https://www.urmc.rochester.edu/encyclopedia/content.aspx?
[7] https://pubmed.ncbi.nlm.nih.gov/24203773/
[8] https://pubmed.ncbi.nlm.nih.gov/14592218/
[9] https://www.colgate.com/en-ph/oral-health/teeth-whitening/does-tea-stain-teeth
[10] https://crest.com/en-us/oral-care-tips/teeth-stains/
[11] https://www.efsa.europa.eu/en/press/news/180418
[12] https://pubmed.ncbi.nlm.nih.gov/24419562/
[13] https://pubmed.ncbi.nlm.nih.gov/28118673/
[14] https://senchateabar.com/blogs/blog/green-tea-side-effects
[15] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1964900/
[16] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5093162/

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