Effects and Mechanisms of Tea on Parkinson's Disease, Alzheimer's Disease and Depression

Neurodegenerative and neuropsychiatric diseases have attracted global attention with an overwhelming burden on families and society. Tea contains many bioactive compounds, such as polyphenols and theanine, which could contribute to the neuroprotective effects of tea. The possible mechanisms of action include regulating signaling pathways and gut microbiota; inhibiting abnormal protein aggregation; normalizing the hyperactivity of the hypothalamic-pituitary-adrenal axis; as well as antioxidant and anti-inflammatory properties of tea for Parkinson's disease, Alzheimer's disease, and depression. In this narrative revie w, the effects of tea on these diseases were summarized, and special attention was paid to the mechanisms of action.