Recycling reactions of natural vitamin E (alpha-tocopherol) by catechins contained in green tea were studied with a double-mixing stopped-flow spectrophotometer. The second-order reaction rate constants of the catechins and deuterated analogues were determined by using a simulation, the activation energies were obtained from the temperature dependences, and the deuterium kinetic-isotope effects were examined. From these results, a tunneling effect was found to play an important role in the vitamin E recycling reactions by the catechins, and the structure-activity relationship was clarified. Furthermore, conditions under which the tunneling effect manifests itself in various vitamin E recycling reactions in biological systems and foods were suggested. A new alpha-tocopherol-recycling capacity assay-method was also proposed, and named an ATREC assay-method after the acronym.