What Causes Oxidative Stress? Oxidative stress may be due to either decreased levels of antioxidants or increased levels of reactive oxygen species in the body. It is linked to cancer, cardiovascular disease, aging, and neurodegenerative diseases such as Parkinson's and Alzheimer's disease. Tobacco smoke is a known source of reactive oxygen species that can overwhelm the normal antioxidant defenses of the individual, resulting in oxidative stress. Increasing antioxidant levels could prevent this scenario. In the China arm of the study, army recruits drank three cups of green tea a day and were allotted 6 cigarettes a day to smoke after meals. After one week, the smokers showed a “dramatic decrease in reactive oxygen species and oxidative stress, Dr. Klaunig said. Tea, particularly green tea, has received a great deal of attention because tea polyphenols are strong antioxidants, and tea preparations have shown inhibitory activity against tumorigenesis. Evidence from experimental studies (in vitro animal and human trials) suggested that regular high-level intake (>3 cups per day) of green tea may be protective against tobacco carcinogens and may reduce the risk of smokers developing lung cancer. Source: James E. Klaunig, PhDPubMed