Theanine: a phytochemical candidate for neural protection.

Theanine, which accumulates in Camellia sinensis (L.) O. Kuntze, has demonstrated strong neuroprotective effects and other health benefits that have attracted attention. This paper reviews relevant literature published during the past 5 years, analyzing and summarizing studies focusing on the neuroprotective functions of theanine. By alleviating neuroinflammation, theanine exerts therapeutic effects on mental disorders caused by cumulative stress, ranging from mild sleep disturbances to depression induced by sleep deprivation. It has also demonstrated beneficial effects in delaying disease progression and promoting repair in age-related neurodegenerative diseases such as Parkinson's disease and Alzheimer's disease. This paper also reviews studies investigating the protective effects of theanine against organ dysfunction caused by nerve injury, as well as its synergistic effects with other phytochemical components in promoting neurological health. The potential mechanisms underlying the neuroprotective effects of theanine are considered from three perspectives: ferroptosis induced by oxidative stress in neuronal cells, the differentiation and development of neural stem cells (NSCs), and neural signal transduction pathways. Further investigations are needed to achieve a more rigorous and comprehensive understanding of theanine. © 2026 Society of Chemical Industry.