Free radicals are thought to be the main cause of cancerous diseases. Free radicals are very active forms of oxygen with strong oxidising properties that destroy human cell membranes and DNA in a cellular process known as oxidative stress. This is responsible for many diseases connected with ageing, sagging of the skin, and deterioration of sight, as well as malignant tumours. Antioxidants are substances which protect the organism from the harmful effects of free radicals. The human body’s ability to produce natural antioxidants decreases with age. Blueberry fruit, however, is a rich source of antioxidants. Vitamins C and F and anthocyanins are all anti-oxidising compounds and they are present in blueberry. American blueberry exhibits greater anti-oxidising activity than any other fruit, according to the Human Nutrition Research Center of the United States Department of Agriculture. Research based on ORAC (Oxygen Radical Absorbance Capacity) tests has demonstrated that blueberry fruit exhibits a significantly greater anti-oxidation operation than do other fruits and vegetables. Hence, they help prevent cancers and diseases of the circulatory system, and help maintain elastic skin and good eyesight.