The sampling of the findings below indicates some of the points that have been made about the relation between tea and health. The research so far has been scattered and unsystematic in that each group seems to investigate what interests it without and comprehensive plan. Reports are fragmentary, results are sometimes contradictory, and methodology varies. It is often impossible to compare studies on the efficacy of the various kinds of teas because different criteria were used in evaluating them. The victory over fatigue that tea provides is a big reason for its popularity.
Caffeine is what does it, and caffeine has been a matter of controversy.
A stimulant, caffeine has been shown to speed reaction time, increase alertness, and improve concentration. The original intake of caffeine causes the body to create stimulant chemicals, catecholamines, that relay nerve impulses to the brain. The height of this effect lasts from 15 to 45 minutes. After six hours the body has eliminated half of the caffeine. If this can be described as a spiritual benefit, then the physical effects include stimulation of digestive juice, metabolism, and the kidneys in ways that possibly help eliminate toxins.