Over the years, it has become obvious that use of green tea is not without adverse effects. Studies of the side effects of green tea specifically are limited. However, green tea is a source of caffeine, for which multiple reactions are reported.
There have been numerous side effects associated with the use of this supplement and they include:
Allergy: Skin rash, redness, itching and hives have all been reported with green tea. It is believed that the tannins in the tea are the culprits. For those individuals who do have hypersensitivity to caffeine or tannin, green tea is best avoided.
CNS stimulation: One of the major components in green tea is caffeine and this chemical is a brain stimulant. Caffeine can cause increased alertness and insomnia. Many individuals complain of lack of sleep after drinking green tea late at night. Most individuals also show evidence of increased alertness. However, excess caffeine can also cause hyper excitability, anxiety and agitation.
Kidney: Caffeine acts on the kidneys as a diuretic (increasing urine and excretion of sodium/potassium), and may worsen the urge to avoid urine.
Ulcers: Caffeine-containing beverages may potentiate the production of stomach acid, and worsen ulcer symptoms.
Constipation: Tannin in tea can cause constipation.
Heart: Caffeine in high doses can increase heart rate and blood pressure. However, this effect is not seen in all individuals
Sugar: An increase in blood sugar levels may occur after excess ingestion of green tea. Caffeine-containing beverages such as green tea should be used cautiously in individuals with diabetes. In contrast, in some individuals, lowering of blood sugar has also been reported.
Liver: individuals with severe liver disease should use caffeine cautiously. Since the damaged liver is unable to breakdown the caffeine, high levels may persist in the body for long periods.
Skin rashes have been associated with caffeine ingestion.
Blood clots: Caffeine is known to affect the ability of the body to form clots but this has not been thoroughly studied in humans.
Caffeine toxicity may occur with high doses. Doses greater than 1,000 milligrams may be fatal. Chronic caffeine consumption can cause intolerance, psychological dependence, and may be habit forming. Abrupt discontinuation may result in withdrawal symptoms.
Excess consumption of green tea has also been linked to a decrease in body iron levels, leading to anemia. This is more noticeable in infants
There is some research that reveals that green tea can also affect the female sex hormones. This effect is currently being studied to determine if there is a relationship between green tea and post menopausal symptoms.
Pregnancy and Breastfeeding: Large amounts of green tea should be used cautiously in pregnant women, as caffeine can cross the placenta. Caffeine has been associated with spontaneous abortion, intrauterine growth retardation, and low birth weight.
Since caffeine is readily transferred into breast milk, its use in breast feeding females should be limited or avoided