Much is written about the health benefits of drinking green tea. These mainly come from their antioxidant such as EGCG, essential oil, vitamin, mineral and caffeine content, and benefits include lowering the risk of cancer and lowering the amount of DNA damaging free radicals in the body. But what is known about the possible harmful side effects of green tea?

Harmful Aspects of Drinking Green Tea

There are a few compounds in green tea that can have ill effects if consumed in large amounts (though some of these are more than beneficial in moderate amounts).

1. Caffeine
2. Polyphenol effect on iron availability to the body
3. Aluminum content

With regards to caffeine the amounts seen in green tea (about 20mg/150ml) are much less than those in coffee (about 100mg/150ml). However this small amount has been shown to have stimulatory effects in moderate coffee consumers. Some people are required to follow a caffeine free diet, the quantities of caffeine in both green and black (about 55mg/150ml) teas are significant to these people. Some of the side effects of caffeine over indulgence include loss of sleep, headaches and increased nervousness.

Aluminium Levels in Green Tea

The presence of aluminium in significant quantities in the leaves of tea may be very important to people who have problems with their renal system and cannot dispose of aluminium correctly. If aluminium builds up in the body it may lead to neurodegenerative diseases such as Alzheimer's. The aluminium concentrations are up to 200 times higher in teas than they are in coffee. This is because the tea plant readily absorbs aluminium from the soil.

Catechin Affinity for Iron

Although polyphenols such as flavonols are responsible for many of the benefits of green tea, these catechins have an affinity for iron when they are drank at the same time as meals are taken, and may lead to the availability of the metal to the body being decreased. It is therefore thought by many that green (or black) tea should not be drank by people who have anaemia. The side effects of green tea's catechin affinity to iron can be reduced by drinking tea between meals or with lemon.

It can therefore be seen that there are a few health issues associated with drinking green tea, it is thought that for most people the numerous health benefits will far outweigh these green tea side effects. As a generalization green tea can be seen as a refreshing drink that will enhance ones health.

References
Cabrera et al. (2006) Beneficial effects of green tea - a review. J. Am. Coll. Nutr. 25: 79 to 99
Flaten (2002): Aluminum in tea concentrations, speciation and bioavailability. Coordin Chem Rev 228:385–395