Guru of Tea

We all know that tea is good for us but where exactly? Externally we are familiar with the image of the reassuring cuppa or glass of tea as a means of relaxing but what physiological effects does tea actually have inside us? In this article we will follow the journey that tea takes through the human body. Tea contains polyphenols (catechins, theaflavins, thearubigins), fluoride, amino acids and of course water. In addition depending on how you drink it, it may contain sugar, milk, other herbs, spices.

Tea starts taking effect almost immediately in direct contact with the body. This is seen primarily at the beginning of the journey as catechins and other polyphenols are great for oral health. Tea has antibacterial, antiviral and anticariogenic (inhibits dental caries) effects and is a valuable source of fluoride which is good for dental health. Tea catechins can stay in the saliva for over 20 mins so if you have a sore throat you should consider gargling with catechin rich green tea! Tea also acts as a breath freshener reacting with and removing sulphur containing chemicals found in alium-based foods (onions, garlic etc.) that can contribute towards halitosis. All these effects and tea has only just begun it’s journey!

Tea and whatever you have drunk it with (sugar, milk, breakfast, lunch) travels through the esophagus after swallowing to the stomach and enters an environment that is designed to begin the break down and absorption of large macromolecules such as protein, complex carbohydrates. This is carried out through the action of both digestive acids and enzyme activity and the breakdown of proteins e.g. from milk, to smaller units (peptides) begins. Absorption into the blood stream begins in the stomach for items such as catechins, fluoride and water - which is the most abundant chemical in tea and vital for hydration!! Tea is better than plain water as you get all the hydration benefits plus antioxidants and fluoride amongst others!

Some components are absorbed into the blood to a greater or lesser extent through the stomach wall but the bulk of the tea continues into the duodenum the ‘exit’ from the stomach. Here things get interesting! The stomach is acidic, the duodenum is exactly the opposite being basic in nature with its own cocktail of enzymes which further breakdown macro (large) molecules into smaller species, such as peptides into amino acids which are easier to pass into the blood.

Think of the blood stream as a formulae one race track with many ‘pits’ where new or repaired cars can enter. The blood goes round and round through various obstacles (e.g. liver whose job is to modify things in the blood - break up or add something making them more soluble in water) these can then be diverted to urine through the kidneys. Those chemicals that have not been sufficiently modified go round the track again. This is why some chemicals stay in the blood stream longer than others. For example caffeine is removed from the blood stream in under 5 hours from absorption.

Once in the blood the chemicals circulate through the major tissues of the body and those that are more fat soluble can pass through the blood-brain barrier and enter the brain - think caffeine ‘buzz’. The amino acid L-theanine after absorption in the small intestine induces ‘non-drowsy relaxation’ when it crosses over to the brain. In addition to mental stimulation caffeine and the other important chemical in the same group - theophylline stimulates physical aspects such as enhanced fat metabolism and opening the air ways. There is a great deal of research to show that tea consumption can temporarily increase the antioxidant level in the blood. Tea antioxidants, when consumed as part of a balanced diet can play a role in the maintenance of health.

In general the bioactive chemicals will be metabolized into compounds that can be passed through the urine and others (minerals etc.) can be absorbed and stored in other parts of the body (calcium laid down in teeth and bones and iron in red blood cells in the blood).

Moving through the small intestine components from tea continue to be absorbed into the blood stream (catechins, theaflavins, caffeine, water, amino acids etc.). We naturally have bacteria present in the large intestine (‘gut flora’) which further help breakdown large molecules into smaller ones that are more rapidly absorbed. These bacteria also work on tea polyphenols e.g. the thearubigins (TR’s - which can represent up to 80% of the antioxidants in black tea). Studies have shown that after a large dose of polyphenols an elevated level of the antioxidant hippuric acid can be found in the blood stream. Scientists have not fully characterized each stage in the breakdown of TR’s to small polyphenols such as hippuric acid but is fairly certain that the bacteria in the large intestine are key to this process. Without them many of the polyphenols in tea would simply pass through our system giving us little benefit.

So, we have drunk our cup of antioxidants and our body has done it’s best to absorb or convert what is useful and discard what either cannot be used (for example soluble fibre) or the converted waste products of what we have utilized. We are at the end of our journey but nutrients, water, antioxidants and other goodies from tea need to be constantly replenished to keep our body hydrated and healthy - so keep drinking – it’s good for you!!

This article was first published in the Fall ‘08 issue of the US Tea Associations ‘teabits’ newsletterVolume 15, Issue 3