Characteristics and Physiological Effects of Hydroponically Cultured Roots of the Tea Plant (Camellia sinensis)

Green tea has been reported to result in improvements in a range of health parameters. However, most research has only documented the effects of green tea brewed from leaves or leaf extracts. In addition to the leaves, the roots of tea plants also possess unique properties because of their requirements for growth, which may enable them to have useful physiological effects. We used a hydroponic system to grow the plants and explored the physiological effects of the roots, which biosynthesize one of the rarest functional amino acids, theanine (γ-ethylamide-L-glutamic acid). The level of theanine was much higher in the roots than in the leaves, and the roots also differed in other aspects of their chemical composition. We evaluated the effects of tea-root extract on the cognitive function and emotions of aged rats. Our results show that, in the object recognition test, aged rats drinking tea-root extract tended to show improved cognitive function and were more relaxed than the control group, which drank tap water. Furthermore, using a mouse model of human aging, we found that the average life span of mice that consumed the root extract was significantly increased. We suggest that tea roots contain unique components that may improve impaired physiological functions, and we therefore propose tea-root extract as a novel nutraceutical.