Tea and coffee are two of the most commonly drunk beverages after water. Both tea and coffee have some interesting health properties, and are quite similar in this respect. However, the chemistry of tea and coffee reflects some of the differences between the two drinks. The first major difference between tea and coffee is that whilst tea is usually consumed only in its raw state, albeit after being dried or fermented, coffee can be more processed. Filter coffee is perhaps more akin to tea because it is the use of the whole beans to generate a drink, whereas instant coffee is more highly processed. Further, tea is available as fermented black tea as well as dried green tea, and this means there are also more than one form of tea. Therefore comparisons can only be done in the context of the particular drink being consumed. Further, the addition of milk and sugar to tea or coffee can also change the health properties significantly.
One similarity between the two drinks is that they are both high in polyphenols, and these may explain some of the health effects of the two drinks. Polyphenols are antioxidants and may significantly reduce oxidative stress. However, the polyphenols differ between coffee and tea with the former being dominated by the polyphenol chlorogenic acid, whereas the later is dominated by the polyphenol catechins. Another key difference is that tea contains lower amounts of caffeine than coffee, but at the same time also contains the structurally similar theophylline. Tea is also rich in the amino acid L-theanine, something that is not present in coffee. L-theanine is able to cross the blood brain barrier and here it activates alpha waves in the brain, producing a calming effect. The present of L-theanine, and the lower caffeine content may explain the calming effects of tea, compared to the more stimulatory effects of coffee.
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