Antioxidants Presented by Janice Hermann, PhD, RD/LD OCES Adult and Older Adult Nutrition Specialist
Free Radicals • Body uses oxygen in metabolic reactions. • Sometimes oxygen reacts with body compounds and forms unstable molecules called free radicals. • Free radicals can also be formed by environmental factors: • Ultraviolet radiation • Air pollution • Tobacco smoke.
Free Radicals • A free radical has one or more unpaired electrons. • An electron without a partner is unstable and very reactive. • To gain stability, a free radical attacks another stable but vulnerable compound and steals an electron.
Free Radicals • After losing an electron, the previously stable molecule becomes a free radical. • It then it attacks another molecule stealing an electron. • This process results in an electron-stealing chain reaction with one free radical producing another free radical.
Free Radicals • Sometimes free radical attacks can be beneficial. • For example, the immune system uses free radicals as an “oxidative burst” to destroy disease causing viruses and bacteria.
Free Radicals and Disease • However, free radical attacks can also cause extensive damage. • Free radicals especially damage polyunsaturated fatty acids in lipoproteins and in cell membranes. • Free radicals also damage cell proteins (altering functions) and DNA (creating mutations).
Free Radicals and Disease • If free radical damage becomes extensive, health problems can develop. • Oxidative stress has been identified as a causative factor in: • Cognitive performance • Aging process • Development of diseases such as cancer, arthritis, cataracts, and heart disease
Defending Against Free Radicals • The body has several lines of defense against free radical damage. • The body’s natural immune system tries to control the free radical damage, but these systems are not 100 percent efficient. • This system become less efficient with age and free radical damage accumulates.
Defending Against Free Radicals • The immune system utilizes enzymes to disable the damaging effect of free radicals. • The enzymes depends on selenium, copper, manganese, and zinc. • If the diet provides inadequate amounts of these minerals, this weakens this line of defense.
Defending Against Free Radicals • The body also uses antioxidants to protect the body against oxidative damage. • Antioxidants can end the chain reaction of forming new free radicals by donating one of their own electrons. • When antioxidants donate an electron they do not become a free radical because they are stable in either form.
Defending Against Free Radicals • Two antioxidant vitamins the body uses are in defense of free radicals are vitamin E and vitamin C. • Vitamin E protects body lipids (cell membranes and lipoproteins) by stopping the free-radical chain reaction.
Defending Against Free Radicals • Vitamin C protects watery components in the body (fluid in the blood) against free radical damage. • Vitamin C also is especially good at stopping free radicals air pollution and cigarette smoke. • In addition, vitamin C may also restore oxidized vitamin E to its active state.
Defending Against Free Radicals • Dietary antioxidants also non-nutrients including some phytochemicals.
Defending Against Free Radicals • Together, vitamin and mineral nutrients and phytochemicals with antioxidant activity protect against certain diseases and decrease free radical damage by: • Limiting free-radical formation • Destroying free radicals or their precursors • Stimulating antioxidant enzyme activity • Repairing oxidative damage • Stimulating repair enzyme activity
Defending Against Cancer • Cancers occur when cellular DNA is damage causing mutations. • Sometimes this damage is caused by free-radical attacks. • Antioxidants may reduce cancer risk by protecting DNA from oxidative damage. • Many studies report lower cancer rates among people who consume abundant fruits and vegetables rich in antioxidants.
Defending Against Cancer • Diets rich in vitamin C correlated with lower cancer rates, especially cancer of the mouth, larynx, esophagus, and stomach. • Such correlations reflect the benefit of consuming a diet rich in fruits and vegetables and low in fat, but it does not necessarily support taking vitamin C supplements to treat or prevent cancer.
Defending Against Cancer • Protective effect of vitamin E against cancer is less consistent than that for vitamin C. However, people with low vitamin E blood levels E have higher rates of certain types of cancer. • Several studies also report a cancer protective effect of fruits and vegetables rich in beta-carotene and the other carotenoids.
Defending Against Heart Disease • High LDL cholesterol is a major risk factor for cardiovascular disease. • One way LDL cholesterol increases the risk of cardiovascular disease is that free radicals in the arteries oxidize LDL cholesterol. • Oxidized LDL cholesterol accelerates the formation of artery-clogging plaques.
Defending Against Heart Disease • Free radicals also oxidize polyunsaturated fatty acids in cell membranes, initiating additional changes in artery walls which decrease blood flow. • Oxidative damage in artery walls is increased by a diet high in saturated fat or cigarette smoke.
Defending Against Heart Disease • On the other hand, diets high in fruits and vegetables, especially in combination with low saturated fat, increase antioxidant action against LDL cholesterol oxidation which can help decreases the development of atherosclerosis.
Defending Against Heart Disease • Antioxidants, especially vitamin E, may protect against the development of cardiovascular disease. • Epidemiological studies have reported that people who consume diets rich in vitamin E have lower rates of death from cardiovascular disease.
Defending Against Heart Disease • Some studies also suggest that vitamin C protects against LDL cholesterol oxidation, raises HDL, lowers total cholesterol, and improves blood pressure. • Vitamin C may also decrease free radical oxidation in the artery wall that typically follows a high-fat meal.
Foods or Supplements • As previously mentioned in the process of stopping free radicals, antioxidants themselves become oxidized. • To some extent, antioxidants can be regenerated, but still, losses occur.
Foods or Supplements • To maintain free radical defenses, people need to replenish dietary antioxidants on a regular basis. • This raises the question is antioxidants be replenish from foods or supplements?
Foods or Supplements • In making recommendations for antioxidant nutrients, the DRI Committee considered whether studies supported substantially higher antioxidant nutrient intakes to help protect against chronic diseases. • The DRI Committee raised the DRI recommendations for vitamins C and E, but did not support taking vitamin supplements over eating a healthy diet.
Foods or Supplements • Isolated supplements are limited. • Vitamin E supplements, for example, usually contain alpha-tocopherol, but foods provide an assortment of tocopherols among other nutrients, many of which provide protection against free-radical damage.
Foods or Supplements • One factor is research is lacking to determine exactly what component, or combination of components, in foods may beneficial. • Foods – especially fruits and vegetables – not only supply antioxidants, but also fiber and many other vitamins, minerals, and phytochemicals.
Foods or Supplements • Isolated supplements are limited. • Vitamin E supplements, for example, usually contain alpha-tocopherol, but foods provide an assortment of tocopherols among other nutrients, many of which protect against free radical damage.
Foods or Supplements • Furthermore, much more research is needed to define optimal and dangerous levels of intake. • Antioxidants behave differently at various levels of intake.
Foods or Supplements • At physiological levels typical of a healthy diet, act as antioxidants, but at pharmacological doses typical of supplements, act as pro-oxidants, stimulating the production of free radicals. • This is especially likely in the presence of other antioxidants or minerals such as iron.
Foods or Supplements • Demonstrated in two studies investigating whether beta-carotene supplementation would reduce the incidence of lung cancer among smokers. • Studies found the incidence of lung cancer was higher among smokers receiving beta-carotene supplements than those taking a placebo, resulting in an early end to the studies.
Foods or Supplements • Until optimum intake levels of these nutrients can be determined, the risks of supplement use remains unclear. • The best way to add antioxidants to the diet is to eat generous servings of fruits and vegetables daily.
Foods or Supplements • In addition, it’s important not to try to single out one particular food for a specific nutrient, antioxidant, or phytochemcial. • Recommendations are to consume a wide variety of fruits and vegetables in generous amounts daily to get the variety of important compounds these foods have to offer.
References • Wadsworth, 2005. Thomson Wadsworth Publishers. • Understanding Normal and Clinical Nutrition, 7th edition by Sharon R Rolfes, Kathryn Pinna & Ellie Whitney, 2006. Thomson Wadsworth Publishers • International Food Information Council, Functional Foods Fact Sheet: Antioxidants, 2006. www.ific.org, accessed January 2007.