When oxygen free-radicals overwhelm the antioxidant defenses of the body, oxidative stress occurs, producing inflammation. In one study, two groups of people with higher chances of heart disease took 4,000 mg of EPA (eicosapentaenoic acid) or DHA (docosahexaenoic acid) per day, or a placebo. The first group was overweight and had abnormal blood fat levels. The second group had type 2 diabetes and was taking medication for high blood pressure. After six weeks, compared to placebo, researchers found about 20 percent fewer signs of oxidative stress in those who took EPA and about 17 percent fewer signs in those who took DHA. Doctors believe that the anti-inflammatory action of omega-3s lowers oxidative stress and chances of cardiovascular disease.