Tea or Coffee?

     Coffee and soft drinks are a source of good, old caffeine, but it also found in tea. Tea, however, has other substances that also provide a stimulant effect. There are two substances related to caffeine, theobromine and theophylline then there is a rather unique amino acid called L-Theanine, which has some very interesting effects on the brain. 
     Both tea and coffee contain caffeine and therefore have a stimulant-like effect on the brain, but the nature of these effects is quite different. The effect provided by tea is gentle while the effect of coffee is like being kicked. Tea has less caffeine than coffee, but the other three stimulant substances that may provide some sort of synergistic effect.
     Caffeine is the world's most widely used psychoactive substance and coffee, the biggest source of caffeine, also happens to be the biggest source of antioxidants in the western diet, and consuming it has been associated with various health benefits. The second largest source of caffeine worldwide is tea, which tends to provide a moderate amount of caffeine. A strong cup of coffee can provide 100 mg, 200 or even 300 mg of caffeine, a cup of tea may provide 20-60 mg. 
     Caffeine causes stimulation of the central nervous system, increases vigilance and reduces drowsiness. It is also believed to block an inhibitory neurotransmitter called adenosine at certain synapses in the brain, leading to the stimulant effect. Adenosine is believed to increase in the brain throughout the day, building up a kind of a "sleep pressure" and the more adenosine, the greater the tendency to fall asleep. Caffeine partly reverses this effect.
     Theophylline and theobromine are both related to caffeine and belong to a class of organic compounds called xanthines. Both have several physiological effects on the body. Theophylline relaxes smooth muscles in the airway, making breathing easier while also stimulating both the rate and force of contraction of the heart. Theobromine can also stimulate the heart, but it has a mild diuretic effect and improves blood flow around the body, leading to a net reduction in blood pressure. The amounts of these substances in a cup of tea are very small though, so their net effect on the body is probably negligible. Some of the caffeine we ingest is metabolized into theophylline and theobromine, so every time you consume caffeine you increase your levels of these two caffeine metabolites. 
     The last substance, a unique type of amino acid called L-theanine, is by far the most interesting. It is mainly found in the tea plant and is able to cross the blood-brain barrier. L-theanine increases brain waves called Alpha waves, which are associated with alert relaxation. Some studies have suggested that L-Theanine, especially when combined with caffeine, can improve attention and brain function. Due to the L-theanine and its effect on alpha waves in the brain, tea may also be a better choice for those who need to concentrate for long periods of time such as studying or working on the computer.  Coffee is better suited for physical endeavors.