Green tea's claim to fame is its antioxidants, which may help boost the immune system. People drink green tea to fight aging, arthritis, Alzheimer's, cancer, heart disease and many other conditions. But can it prevent the common cold? A 2007 study found the ingredients in green tea can enhance the body's immune system by 28 percent. The antioxidants in green tea are said to be 100 times more effective than vitamin C.