antioxidants and free radicals

antioxidants and free radicals

Antioxidants are protective substances that help to neutralize the damaging effects of oxidative reactions occurring within in our cells. The major dietary antioxidants are the vitamins A, C, E and betacarotene plus the minerals selenium, zinc, copper and manganese. They work by neutralizing damaging free radicals, either on their own or through incorporation into antioxidant enzymes.   WHAT ARE FREE RADICALS? As in politics, a free radical is a highly unstable entity that races round picking fights and causing damage. The chemical version consists of a variety of molecular fragments which carry a negative electrical charge. These unstable free radicals collide with other cell molecules until they achieve stability by neutralizing their charge ­ either through stealing a positive charge from another molecule or by off-loading their own negative one. This process is known as oxidation. It is estimated that every cell in our body is subjected to 10,000 free radical oxidations per day. This is potentially serious as: • Oxidized cholesterol is more likely to stick to artery walls and fur them up. • Oxidized DNA can trigger gene mutations and cancers. • Oxidization within the eye lens may trigger cataracts. • Oxidized cell membranes and fats lead to premature wrinkling and skin ageing. • It is estimated that 40 per cent of sperm damage is due to the harmful effects of free radicals. Oxidized DNA in sperm can lead to: • subfertility • developmental abnormalities in offspring • an increased risk of childhood cancers in offspring. Free radicals are generated by our normal metabolic processes. Men with diabetes whose blood sugars are not tightly controlled generate twice as many free radicals as non-diabetic males. Smokers and others passively exposed to inhaled cigarette smoke or exhaust fumes also generate twice as many as their non-smoking peers. Exposure to X-ray irradiation and to ultra-violet sunlight is a potent source of free radicals due to the energy in these waves activating and damaging cell molecules. This is one reason why both types of rays are linked with cancer. Other environmental agents that generate increased numbers of free radicals are the actions of alcohol and other drugs, especially antibiotics.   ANTIOXIDANTS Antioxidants work by mopping up the negative charge on the free radicals without themselves becoming damaged. Their effects are summative and interlinked ­ for example, vitamin E that has mopped up a free radical is regenerated by a chemical interaction with vitamin C. If we can keep our levels of antioxidants optimally high, most free radicals can be neutralized before they cause any damage. That means ensuring an adequate dietary intake of vitamins C, E and betacarotene, and of the trace minerals selenium, zinc, copper and manganese. Many experts now consider that reference nutrient intakes of antioxidant vitamins are inadequate. They were formulated to prevent deficiency diseases before the important antioxidant functions were understood. The diets of thousands of people have been analysed and their dietary intakes of antioxidants compared with the subsequent incidence of coronary heart disease (CHD) and cancer. Researchers have found that those with the highest dietary antioxidant intakes have the lowest risk of developing these common killer diseases. As a result of this work, the most protective intakes of antioxidant vitamins seem to be: • Vitamin C: 100­250 mg/day • Vitamin E: 30­80 mg/day • Betacarotene: 15 mg/day. Smokers and people with diabetes probably need to double these intakes. Various studies have found that: • The risk of angina is three times higher in men with low intakes of vitamins E, C and betacarotene. • The risk of CHD is reduced by up to 25 per cent in men taking vitamin E supplements for two years or more. • Men with the highest intake of betacarotene have a 25 per cent lower risk of CHD. • A high intake of vitamin C lowers the risk of CHD in men by 40 per cent ­ and the risk of dying from it by 35 per cent. • High intakes of betacarotene also seem to protect against cancers of the mouth, throat, larynx, oesophagus, stomach, large bowel, bladder and lung. Vitamins C, E and betacarotene plus the mineral zinc have their own separate and combined beneficial effects on sperm health (see Chapters 19 and 20). These effects are mostly due to their antioxidant properties.