Role of Green Tea in Brain Aging

Epidemiological studies have demonstrated that the intake of green tea is effective for reducing the risk of dementia. However, it is not clear which components of green tea reduce that risk, and how they act. The most important risk factor for dementia is brain aging. Therefore, our research has focused on the role of green tea in preventing brain aging. Epigallocatechin gallate(EGCG) is the most significant component in green tea. Although both EGCG and epigallocatechin (EGC) have been shown to pass the blood–brain barrier and reach the brain parenchyma, EGCG has been proven to be more effective at promoting neuronal differentiation than EGC. It's also been proposed that the products of EGCG deconstruction by the gut microbiota enhance nerve cell development, and that both EGCG and its degradation products act on nerve cells, albeit with a time lag. On the other hand, the free amino acids theanine and arginine present in green tea have stress-reducing effects. While long-term stress accelerates aging of the brain, theanine and arginine suppress this aging due to their anti-stress effect. Since this effect is counteracted by EGCG and caffeine, the ratio of these green tea components is important for the anti-stress action. Based on these findings, it is thought that the suppression of brain aging by green tea through activation of neurons by EGCG and its degradation products, and the reduction of stress by theanine and arginine, may be involved in reducing the risk of dementia.