Green tea has been shown to improve blood flow and lower cholesterol. A 2013 review of many studies found green tea helped prevent a range of heart-related issues, from high blood pressure to congestive heart failure.
What’s good for the heart is usually good for the brain; your brain needs healthy blood vessels, too. In one Swiss study, MRIs revealed that people who drank green tea had greater activity in the working-memory area of their brains. Green tea has also been shown to help block the formation of plaques that are linked to Alzheimer's disease.
Studies on green tea’s impact on cancer have been mixed. But green tea is known to aid healthy cells in all stages of growth. There are some clues that green tea may help destroy cancer cells, but that research is still in its early stages, so you shouldn’t count on green tea to prevent cancer. In fact, the National Cancer Institute's web site says it "does not recommend for or against the use of tea to reduce the risk of any type of cancer."