Antioxidants

Presented by Janice Hermann, PhD, RD/LD

OCES Adult and Older Adult Nutrition Specialist

Free RadicalsBody 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 radiationAir pollutionTobacco 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 RadicalsAfter 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 RadicalsSometimes 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 DiseaseHowever, 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 DiseaseIf free radical damage becomes extensive,

health problems can develop. Oxidative stress has been identified as a

causative factor in:Cognitive performanceAging processDevelopment of diseases such as cancer, arthritis,

cataracts, and heart disease

Defending Against Free RadicalsThe 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 RadicalsThe 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 RadicalsThe 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 RadicalsTwo 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 RadicalsVitamin 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 RadicalsDietary 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 formationDestroying free radicals or their precursorsStimulating antioxidant enzyme activityRepairing oxidative damageStimulating repair enzyme activity

Defending Against CancerCancers 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 CancerDiets 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 CancerProtective 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 DiseaseHigh 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 DiseaseFree 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 DiseaseOn 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 DiseaseAntioxidants, 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 DiseaseSome 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 SupplementsAs 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 SupplementsTo 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 SupplementsIn 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 SupplementsIsolated 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 SupplementsOne 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 SupplementsIsolated 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 SupplementsFurthermore, much more research is needed

to define optimal and dangerous levels of intake.

Antioxidants behave differently at various levels of intake.

Foods or SupplementsAt 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 SupplementsDemonstrated 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 SupplementsUntil 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 SupplementsIn 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.

ReferencesWadsworth, 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.