Green tea is a healthful beverage, rich in antioxidants and nutrients, yet it's possible to suffer negative health effects from drinking too much. Here's a look at the chemicals in green tea that can cause harm and how much green tea is too much.
Adverse Effects From Chemicals in Green Tea
The compounds in green tea responsible for most negative health effects are caffeine, the element fluorine, and flavonoids. The combination of these and other chemicals may cause liver damage in some persons or if you drink a lot of tea. Tannins in green tea reduce the absorption of folic acid, a B vitamin that is particularly important during fetal development. Also, green tea interacts with several medications, so it's important to know whether or not you can drink it if you take prescription or over the counter drugs. Caution is advised if you take other stimulants or anticoagulants.
Caffeine in Green Tea
The amount of caffeine in a cup of green tea depends on the brand and how it is brewed but is around 35 mg per cup. Caffeine is a stimulant, so it increases heart rate and blood pressure, acts as a diuretic, and increases alertness. Too much caffeine, whether from tea, coffee, or another source, can lead to rapid heartbeat, insomnia, and tremors, to stimulant psychosis or even death. Most people can tolerate 200-300 mg of caffeine. According to WebMD, the lethal dose of caffeine for adults is 150-200 mg per kilogram, with serious toxicity possible at lower doses. Excessive consumption of tea or any caffeinated beverage can be extremely dangerous.
Fluorine in Green Tea
Tea is naturally high in the element fluorine. Drinking too much green tea can contribute unhealthy levels of fluorine to the diet. The effect is particularly pronounced if the tea is brewed with fluoridated drinking water. Too much fluorine can lead to developmental delays, bone disease, dental fluorosis, and other negative effects.
Flavonoids in Green Tea
Flavonoids are potent antioxidants that help protect cells from free radical damage. However, flavonoids also bind nonheme iron. Drinking too much green tea limits the body's ability to absorb essential iron. This can lead to anemia or a bleeding disorder. According to the Linus Pauling Foundation, routinely drinking green tea with meals can reduce iron absorption by 70%. Drinking tea between meals rather than with food helps to reduce this effect.
How Much Green Tea Is Too Much?
The answer to this question depends on your personal biochemistry. Most experts advise against drinking more than five cups of green tea per day. Pregnant and nursing women may wish to limit green tea to no more than two cups per day.
For most people, the benefits of drinking green tea outweigh the risks, but if you drink too much green tea, are sensitive to caffeine, suffer anemia, or take certain medications, you may experience serious negative health effects. Just as it's possible to die from drinking too much water, it's possible to drink a lethal volume of green tea. However, caffeine overdose would be the primary risk.
- Fluorine Safety References, Purdue University Department of Chemistry (retrieved 03/01/2015)
- WebMD Green Tea Side Effects (retrieved 03/01/2015)
- Linus Pauling Foundation, Oregon State University