Green tea is considered one of the world’s healthiest drinks and contains one of the highest amounts of antioxidants of any tea. Natural chemicals called polyphenols in tea are what are thought to provide its anti-inflammatory and anti-carcinogenic effects. Green tea is approximately 20-45 percent polyphenols by weight, of which 60-80 percent are catechins such as EGCG. Catechins are antioxidants that are said to help prevent cell damage.
Unsweetened brewed green tea is a zero calorie beverage. The caffeine contained in a cup of tea can vary according to the length of infusing time and the amount of tea infused. Green tea contains about 30 to 50 milligrams of caffeine per 8 oz cup, but a percentage of caffeine content in green tea vary according to the area of cultivation and the growth stage of the leaf. For example, the younger leaves and buds have greatest caffeine content, and older leaves have correspondingly larger amounts of caffeine., compared with black tea, which contains about 50 milligrams and coffee with 95 milligrams per cup.
Green tea has also been linked to an increase in the number of calories burned. The caffeine and antioxidants stimulate the metabolism and aid the oxidation of fat. The combination of green tea and caffeine improved weight loss.
Types of green tea
Green tea is available in many types, including:
- bottled and sweetened with sugar or an artificial sweetener
- in single tea bags
- as loose-leaf
- in instant-powder
- green tea supplements, which are sold in capsule form or liquid extracts
According to 2010 research presented at the American Chemical Society, bottled teas are not equivalent to brewed teas as some 16 ounce bottled teas can contain fewer polyphenols than one cup of brewed tea.
Green tea side effects and risks
There are little to no known side effects or contraindications to drinking green tea for adults. However, the following risks or complications should be made clear:
- Caffeine sensitivity – those with severe caffeine sensitivities could experience insomnia, anxiety, irritability, nausea, or upset stomach.
- Blood thinners – those taking blood thinners (anticoagulant drugs) such as Coumadin/warfarin should drink green tea with caution due to its vitamin K content. It’s also recommended to avoid green tea and aspirin, because they both reduce the clotting effectiveness of platelets.
- Other stimulants – if taken with stimulant drugs, green tea could increase blood pressure and heart rate.
Green tea supplements contain high levels of active substances that can trigger side effects and interact with other herbs, supplements, or medications.
Green tea supplements are unregulated by the FDA and may also contain other substances unsafe for health or with unproven health benefits. Always check with a doctor before starting any herb or supplement regimen.
In particular, pregnant or breastfeeding women, those with heart problems or high blood pressure, kidney or liver problems, stomach ulcers, or anxiety disorders should not take green tea supplements or extracts.
Further reading on green tea
Various green tea products are available to purchase online. It is a good idea to compare different brands, and different types of green tea, to choose the most suitable one for you.
Have you enjoyed reading about the potential health benefits of green tea? Take a look at our collection of articles about other fruits and vegetables.