Green tea (Camellia sinensis) belongs to the family Theaceae and is used most popularly as beverage all over the world. Although moderate green tea consumption is typically healthy but drinking too much may lead to side effects such as nausea, vomiting, dehydration, lethargy, central nervous system stimulation such as dizziness, insomnia, tremors, restlessness, confusion, diuresis, heart rate irregularities and psychomotor agitation. Epigallocatechin-3-gallate (EGCG), the most abundant polyphenol in green tea has anti-folate activity so to prevent folate deficiency it should not used in excessive quantity and it may also reacts with some drugs like aspirin and MAOI so used with caution if high level of green tea is used.
Green tea is cultivated commercially in Asia, Africa and South America. Dissimilar black tea, which is fermented, green tea is produced in a non-fermented procedure. It may be used in the form of a brewed drink or capsular extract. Presently, there is no proper dose suggested for green tea extract. The main active ingredients of green tea include polyphenolic compounds such as epicatechin (EC), epicatechin-3-gallate (ECG), epigallocatechin (EGC) and epigallocatechin-3-gallate (EGCG), all of which may be responsible for the anti-carcinogenic and anti-mutagenic activities of green tea. Other polyphenols in green tea include flavanols and their glycosides and depsides such as chlorogenic acid, quinic acids, carotenoids, trigalloylglucose, lignin, protein, chlorophyll, minerals, caffeine and a very small amount of methylxanthines. Drinking green tea has several benefits, but there are potential side effects associated with excessive use of green tea.
Green tea contains about 30 to 60 mg of caffeine per 6 to 8 oz. cup. This is normal and less than the average 100 mg caffeine contained in a cup of coffee. But green tea is generally consumed in greater amounts when used for weight loss and this increases the consumption of caffeine. And if more than five cups of tea per day are used, it will raise caffeine intake to unsafe levels, and may increase risk for insomnia, restlessness, tremors, and upset stomach. Tannins present in green tea bind with non-heme iron in the body and it is not as easily absorbed in the body as heme iron and can lead to iron deficit anemia. American Association of Cancer Research study on the antifolate activity of tea showed that EGCG can interfere with folate use in cells. Folate is needed to make DNA and prevent negative changes to DNA from cancers. Folate also helps to make red blood cells, protect against heart disease and prevent anemia. It is important to be aware of green tea intake to prevent folate deficiency. Green tea is also a natural diuretic so; by drinking extreme amounts of green tea (more than five cups /day) it can cause excessive urination leading to dehydration and electrolyte disproportion. Dehydration can also leads to headaches, lethargy, changed heart rate and distress. Green tea can also interfere with the absorption and effects of certain medications. This can lessen or intensify the effects of medications, which could put your health at risk. Some medications that might be affected include MAOI inhibitors, lithium, adenosine and blood thinners.
Depending on the brand, two to three cups of green tea per day (for a total of 240–320 mg polyphenols) or 100–750 mg per day of standardized green tea extract is recommended. Pharmacological and toxicological evidence indicate that green tea polyphenols can in fact cause oxidative stress and liver toxicity in vivo at certain concentrations. Patients on Warfarin should not take green tea because green tea having vitamin K. Green tea must not to be delivering with aspirin in light of the fact that it keeps platelets from coagulation. So, peoples who are consuming green tea in large amounts or those who are using it to reduce weight should use it cautiously to prevent the side effects associated with green tea.
Source
Nawab, A. and Farooq, N. 2015. Review on green tea constituents and its negative effects. The Pharma Innovation Journal, 4(1): 21-24; ISSN: 2277- 7695.