1) How much theine/caffeine is there in tea/coffee?
Black tea (15 cl) contains approximately 50 mg theine. But it’s possible to reach 100 mg per cup with more tea leaves and longer steeping time. Green spring tea is extra rich in theine, whereas oolong tea contains a relatively small amount.
There is approximately 95 mg caffeine in a cup of coffee (12.5 cl) according to the Swedish Coffee Information website (Svensk Kaffeinformation). This suggests that a cup of coffee contains about twice as much caffeine as a cup of tea. The amount of caffeine/theine can however vary depending on brewing method etcetera.
Herbal teas and rooibos (red tea) does not contain any caffeine. It’s also possible to produce caffeine-free tea, but this will be done at the expense of the flavour. Rooibos is a better alternative for those who look for a caffeine-free alternative.
Caffeine (in coffee) and theine (in tea) is exactly the same substance.
2) Is tea a wholesome beverage?
Yes, researchers say that tea is a healthy beverage. Tea is very rich in antioxidants that are believed to be able to prevent disease and ageing. The amount antioxidants in one cup of tea is equal to approximately two apples or seven glasses of orange juice.
3) Could tea be farmful?
Yes, it could. The biggest risk with drinking large amounts of tea is probably to overdose theine or fluoride. A lethal dose of caffeine is believed to be equal to approximately 100 cups of coffee.
Some teas may also contain a large amounts of fluoride due to the increasing environmental pollution. Approximately 1 mg/L prevents tooth decay, whereas a long-term exposure to approximately 5 mg/L could be harmful for teeth and skeleton. It could cause dental and skeletal fluorosis.
See for example Skeletal Fluorosis Due to Excessive Tea Drinking that was published in The New England Journal of Medicine on March 21, 2013. A woman, who during the past 17 years drank extreme amounts of tea equivalent to 100–150 tea bags per day – that is over 20 mg fluoride per day according to the researchers – lost all of her teeth. And the radiography furthermore showed skeletal abnormalities.
Extreme amounts of tea can therefore be harmful, just like everything else. A more normal consumption of 3–5 cups per day is however considered wholesome.
4) When should I avoid / minimize the intake of tea?
According to Chinese literature, the polyphenols (antioxidants) in tea may worsen problems with constipation and gastric ulcer.
Tea should not be taken with medicine, since the polyphenols and theine could react with the medicine.
Caffeine intake for pregnant women should not be higher than 300 mg/day according to the Swedish National Food Agency (Livsmedelsverket).
Tea should not be drunk with food if you suffer from iron deficiency. The polyphenols in tea could reduce the absorption of calcium and non-heme iron (in vegetables). This is however normally not a problem for healthy individuals.