One way to think of oxidative stress is to think of the chemicals that cause it as firing electrons, which are like little chemical bullets. Nutrients that we call antioxidants are like little bullet-proof vests that protect the cells. Oxidative stress can cause the dementia that comes with aging. Polyphenols are powerful antioxidants that are found in green tea.
Research appearing in Biogerontology (Sept 7, 2006) found that consumption of polyphenols from green tea may prevent oxidative damage to brain cells and help delay memory loss. From the age of 1 month until the age of 15 months, mice were fed water that contained a 0.02% concentration of polyphenol from green tea. The extract acted to prevent memory loss and oxidative damage to DNA.