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Drinking too much green tea may cause the adverse effects associated with caffeine intake. These include anxiety, accelerated heart rate, and sleep disturbances. L-theanine found in green tea can in turn cause dizziness, headaches, and digestive problems.
Due to the effects of caffeine on heart rate, people suffering from heart conditions, as well as pregnant and breastfeeding women, should drink green tea in moderation.
Because caffeine has diuretic effects, people on diuretics should drink green tea in moderation.
Some studies have revealed the capacity of tea plants to accumulate high levels of aluminum. This heavy metal may build up in the body and cause brain and kidney damage. To reduce your potential exposure to aluminum, make sure to obtain green tea from reputable sources.
Although rare, excessive epigallocatechin gallate (over 400 mg/day) can cause liver toxicity and even liver failure.
Tea polyphenols reduced iron absorption in rats. People with anemia may want to cut down on green tea intake.
Epigallocatechin gallate acted as a pro-oxidant, rather than an antioxidant, in the pancreatic insulin-secreting cells of diabetic mice. Further clinical studies should determine its safety in people with type 2 diabetes.
In rats, green tea consumption lowered testosterone levels by 20% and sperm count by 2%, suggesting its potential to reduce male fertility.
At high doses, green tea extract induced thyroid enlargement (goiter) and altered thyroid function in rats. However, people drinking green tea are unlikely to reach these doses.
Drug and Supplement Interactions
Supplement/Herb/Nutrient-drug interactions can be dangerous and, in rare cases, even life-threatening. Always consult your doctor before supplementing and let them know about all drugs and supplements you are using or considering.
- Fish oil: its combination with green tea catechins may increase fat and glucose metabolism.
- Ubiquinone: this supplement increased the antioxidant effects of epigallocatechin gallate in rats.
- Curcumin: its combination with epigallocatechin gallate reduced cancer cell growth.
- Capsicum vanilloids: found in hot peppers, capsicum vanilloids help kill cancer cells. Their combination with green tea had synergistic effects.
- Vitamin E: its combination with green tea polyphenols improved exercise capacity, lowered glucose levels, and reduced body weight in humans. *
