In studies at the USDA Human Nutrition Research Center, blueberries ranked highest in disease-fighting antioxidants when compared to 40 other fresh fruits and vegetables. Antioxidants work by neutralizing free radicals, the byproducts of metabolism that can damage cells and DNA and lead to some forms of cancer, heart disease, stroke and other chronic diseases of aging. Anthocyanins, the pigments that give blueberries their beautiful color, also give them their high antioxidant activity.