The effect of tea on your body depends largely by the growth stage of the leaf, the brewing time, the amount of tea used and a person's sensitivity to tea's ingredients.
The stimulating effect of a tea is mainly due to what is called alkaloid caffeine which is then linked with tannin found in a tea leaf.
Almost the entire amount of caffeine is dissolved during the infusion within the first 1-2 minutes because caffeine dissolves well in hot water. This is without the tannin.
This short brewing time results to a brew with a high level of caffeine not related to tannin. If the tea is brewed for a longer time about 4-8 minutes, the tannin as well as other ingredients start to dissolve gradually. This results, however, to a stronger brew.
Tannin has the ability to prevent or delay the caffeine from being absorbed quickly in the stomach or intestines.
It has been found that this delayed effect can stretch the cumulative effect of caffeine to 10-12 hours with frequent, daily tea-drinking.
So, if you want a more stimulating effect of a black tea or green tea, consider a short brewing time and if you only want a slightly stimulating effect, have a longer brewing time.
The caffeine of a tea can be reduced by pouring a little boiling water over the amount of tea to be used and then sieving this off after half a minute.
When not consumed in excess, tea can have a stimulating effect but not irritating unlike other beverage. This stimulating effect does not raise blood pressure. However, an excess intake of caffeine can cause an increase in blood pressure.
A recommended amount of tea to use is a maximum of one level teaspoon per cup of tea leaves with a longer brewing time about 4-6 minutes. This can be consumed naturally without the use of artificial sweeteners or sugar.
A tea left for a shorter time only results to a milder brew.