The caffeine and catechins in green tea are well known for their health benefits, but they can also cause side effects for some people, especially in large doses.
Effects of Caffeine
Consuming too much caffeine can increase feelings of anxiety, interfere with sleep and cause stomach upset and headaches in some people.
Consuming large amounts of caffeine while pregnant may even increase the risk of birth defects and miscarriage.
Based on current research, everyone, including pregnant women, should not consume more than 300 mg of caffeine daily.
However, one review looked at over 400 studies and found that healthy adults who consumed up to 400 mg of caffeine per day did not experience adverse effects .
The amount of caffeine in one cup of green tea varies depending on the amount of tea used and the length of time the leaves steep.
One study found that the caffeine content of 1 gram of green tea ranged from 11–20 mg.
A single serving is usually measured at 1 tablespoon (2 grams) of tea leaves per 1 cup (240 ml) of water. Assuming each cup of tea is approximately 1 cup (240 ml), this means the average cup of green tea contains about 22–40 mg of caffeine.
Catechins May Reduce Iron Absorption
The catechins in green tea may reduce your ability to absorb iron from foods.
In fact, consuming catechins in large quantities may lead to iron deficiency anemia.
While regularly drinking green tea isn’t a concern for most healthy individuals, those at risk of iron deficiency should consider drinking tea in between meals and waiting at least one hour after eating before drinking tea.
Infants, young children, women who are pregnant or menstruating and individuals who have internal bleeding or are undergoing dialysis are all at an increased risk of iron deficiency.
The catechins in green tea can also interfere with certain medications and decrease their effectiveness.
For example, studies indicate that green tea may inhibit the effectiveness of certain heart and blood pressure medications.
Drinking green tea may also decrease the effects of certain medications used to treat anxiety and depression.
Toxic effects are most common when people take green tea supplements, which have a much higher concentration of catechins than green tea itself.
SUMMARY: When consumed in moderation, green tea is safe for most people. You may want to limit or avoid it if you have iron deficiency or are pregnant, nursing or taking medications for anxiety disorders or heart conditions.
Green tea is packed full of health-promoting compounds.
Regularly drinking green tea can help you lose weight and reduce your risk of several diseases, including diabetes, heart disease and cancer.
Drinking three to five cups of green tea per day seems to be optimal to reap the most health benefits.
Very high doses may be problematic for some, but generally, green tea’s benefits far outweigh its risks.
In fact, drinking more green tea may greatly improve your health.