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Vitamin E: Anti-oxidant FunctionAntioxidant properties -
Some substances that act as antioxidants in one situation may be pro-oxidants—electron grabbers—in a different situation. Another big misconception is that antioxidants are interchangeable. Each one has unique chemical behaviors and biological properties.
They almost certainly evolved as parts of elaborate networks, with each different substance or family of substances playing slightly different roles. This means that no single substance can do the work of the whole crowd.
Antioxidants came to public attention in the s, when scientists began to understand that free radical damage was involved in the early stages of artery-clogging atherosclerosis.
It was also linked to cancer , vision loss, and a host of other chronic conditions. Some studies showed that people with low intakes of antioxidant-rich fruits and vegetables were at greater risk for developing these chronic conditions than were people who ate plenty of those foods. Clinical trials began testing the impact of single substances in supplement form, especially beta-carotene and vitamin E, as weapons against chronic diseases.
Supplement makers touted the disease-fighting properties of all sorts of antioxidants. The research results were mixed, but most did not find the hoped-for benefits. Antioxidants are still added to breakfast cereals, sports bars, energy drinks, and other processed foods , and they are promoted as additives that can prevent heart disease, cancer, cataracts, memory loss, and other conditions.
Randomized placebo-controlled trials, which can provide the strongest evidence, offer little support that taking vitamin C, vitamin E, beta-carotene, or other single antioxidants provides substantial protection against heart disease, cancer, or other chronic conditions.
The results of the largest trials have been mostly negative. A modest effect of vitamin E has been found in some studies but more research is needed. A study from the Journal of Respiratory Research found that different isoforms of vitamin E called tocopherols had opposing effects on lung function.
Lung function was tested using spirometric parameters: higher parameters are indicative of increased lung function, while lower parameters are indicative of decreased lung function.
The study found that higher serum levels of alpha-tocopherol were associated with higher spirometric parameters and that high serum levels of gamma-tocopherol were associated with lower spirometric parameters. Though the study was observational in nature, it confirmed the mechanistic pathway of alpha- and gamma-tocopherol in mice studies.
When it comes to cancer prevention, the picture remains inconclusive for antioxidant supplements. Few trials have gone on long enough to provide an adequate test for cancer. High-dose antioxidant supplements can also interfere with medicines.
Vitamin E supplements can have a blood-thinning effect and increase the risk of bleeding in people who are already taking blood-thinning medicines. Some studies have suggested that taking antioxidant supplements during cancer treatment might interfere with the effectiveness of the treatment.
Inform your doctor if starting supplements of any kind. One possible reason why many studies on antioxidant supplements do not show a health benefit is because antioxidants tend to work best in combination with other nutrients, plant chemicals, and even other antioxidants.
For example, a cup of fresh strawberries contains about 80 mg of vitamin C, a nutrient classified as having high antioxidant activity. Polyphenols also have many other chemical properties besides their ability to serve as antioxidants.
There is a question if a nutrient with antioxidant activity can cause the opposite effect with pro-oxidant activity if too much is taken.
This is why using an antioxidant supplement with a single isolated substance may not be an effective strategy for everyone. Differences in the amount and type of antioxidants in foods versus those in supplements might also influence their effects.
For example, there are eight chemical forms of vitamin E present in foods. However, vitamin E supplements typically only include one form, alpha-tocopherol. Epidemiological prospective studies show that higher intakes of antioxidant-rich fruits, vegetables, and legumes are associated with a lower risk of chronic oxidative stress-related diseases like cardiovascular diseases , cancer, and deaths from all causes.
The following are nutrients with antioxidant activity and the foods in which they are found:. Excessive free radicals contribute to chronic diseases including cancer, heart disease, cognitive decline, and vision loss. Keep in mind that most of the trials conducted have had fundamental limitations due to their relatively short duration and inclusion of people with existing disease.
At the same time, abundant evidence suggests that eating whole in fruits , vegetables , and whole grains —all rich in networks of naturally occurring antioxidants and their helper molecules—provides protection against many scourges of aging.
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Skip to content The Nutrition Source. The Nutrition Source Menu. Search for:. Home Nutrition News What Should I Eat? In , a rating tool called the Oxygen Radical Absorbance Capacity ORAC was created by scientists from the National Institute on Aging and the United States Department of Agriculture USDA.
It was used to measure the antioxidant capacity of foods. The USDA provided an ORAC database on its website highlighting foods with high ORAC scores, including cocoa, berries, spices, and legumes. Blueberries and other foods topping the list were heavily promoted in the popular press as disease-fighters even if the science was weak, from cancer to brain health to heart disease.
However, 20 years later the USDA retracted the information and removed the database after determining that antioxidants have many functions, not all of which are related to free radical activity.
Although this was not a primary endpoint for the trial, it nevertheless represents an important outcome. In the Heart Outcomes Prevention Evaluation HOPE trial, the rates of major cardiovascular events were essentially the same in the vitamin E A recent trial of vitamin E in Israel, for example, showed a marked reduction in coronary heart disease among people with type 2 diabetes who have a common genetic predisposition for greater oxidative stress.
In the Supplementation en Vitamines et Mineraux Antioxydants SU. MAX study, 13, French men and women took a single daily capsule that contained mg vitamin C, 30 mg vitamin E, 6 mg beta-carotene, mcg selenium, and 20 mg zinc, or a placebo, for seven and a half years.
The vitamins had no effect on overall rates of cardiovascular disease. Lung disease A study from the Journal of Respiratory Research found that different isoforms of vitamin E called tocopherols had opposing effects on lung function. Cancer When it comes to cancer prevention, the picture remains inconclusive for antioxidant supplements.
MAX randomized placebo-controlled trial showed a reduction in cancer risk and all-cause mortality among men taking an antioxidant cocktail low doses of vitamins C and E, beta-carotene, selenium, and zinc but no apparent effect in women, possibly because men tended to have low blood levels of beta-carotene and other vitamins at the beginning of the study.
Age-related eye disease A six-year trial, the Age-Related Eye Disease Study AREDS , found that a combination of vitamin C, vitamin E, beta-carotene, and zinc offered some protection against the development of advanced age-related macular degeneration, but not cataracts, in people who were at high risk of the disease.
However, relatively short trials of lutein supplementation for age-related macular degeneration have yielded conflicting findings. The study found that people taking the vitamins were less likely to progress to late-stage AMD and vision loss.
However, the study authors noted that taking lutein and zeaxanthin alone or vitamin E alone did not have a beneficial effect on these eye conditions.
The Selenium and Vitamin E Cancer Prevention Trial SELECT Eye Endpoints Study, which followed 11, men for a mean of five years, did not find that vitamin E and selenium supplements, in combination or alone, protected from age-related cataracts.
It did not find that antioxidant supplements of vitamin E or selenium, alone or in combination, protected against dementia compared with a placebo. Early death A meta-analysis of 68 antioxidant supplement trials found that taking beta-carotene and vitamin A and E supplements increased the risk of dying.
It was also difficult to compare interventions because the types of supplements, the dosages taken, and the length of time they were taken varied widely. The same authors conducted another systematic review of 78 randomized clinical trials on antioxidant supplements including beta-carotene, vitamin A, vitamin C, vitamin E, and selenium alone or in combination.
The study found that both people who were healthy and those with diseases taking beta-carotene and vitamin E supplements had a higher rate of death. The duration of the studies varied widely from one month to 12 years, with varying dosages.
The first inkling came in a large trial of beta-carotene conducted among men in Finland who were heavy smokers, and therefore at high risk for developing lung cancer.
The trial was stopped early when researchers saw a significant increase in lung cancer among those taking the supplement compared to those taking the placebo. Again, an increase in lung cancer was seen in the supplement group. MAX trial, rates of skin cancer were higher in women who were assigned to take vitamin C, vitamin E, beta-carotene, selenium, and zinc.
These results came from the Selenium and Vitamin E Cancer Prevention Trial SELECT that followed 35, men for up to 12 years. References National Center for Complementary and Integrative Health NCCIH. Antioxidants: In Depth. Carlsen MH, Halvorsen BL, Holte K, Bøhn SK, Dragland S, Sampson L, Willey C, Senoo H, Umezono Y, Sanada C, Barikmo I.
The total antioxidant content of more than foods, beverages, spices, herbs and supplements used worldwide. Nutrition journal. Semba RD, Ferrucci L, Bartali B, Urpí-Sarda M, Zamora-Ros R, Sun K, Cherubini A, Bandinelli S, Andres-Lacueva C.
Resveratrol levels and all-cause mortality in older community-dwelling adults. JAMA internal medicine. Grodstein F, Kang JH, Glynn RJ, Cook NR, Gaziano JM. Archives of internal medicine. USDA Oxygen Radical Absorbance Capacity ORAC of Selected Foods, Release 2 The process of oxidation in the human body damages cell membranes and other structures, including cellular proteins, lipids and DNA.
The body can cope with some free radicals and needs them to function effectively. However, the damage caused by an overload of free radicals over time may become irreversible and lead to certain diseases including heart and liver disease and some cancers such as oral, oesophageal, stomach and bowel cancers.
Oxidation can be accelerated by stress , cigarette smoking , alcohol , sunlight, pollution and other factors. Antioxidants are found in certain foods and may prevent some of the damage caused by free radicals by neutralising them. These include the nutrient antioxidants, vitamins A, C and E, and the minerals copper, zinc and selenium.
Other dietary food compounds, such as the phytochemicals in plants, are believed to have greater antioxidant effects than vitamins or minerals. These are called the non-nutrient antioxidants and include phytochemicals, such as lycopenes in tomatoes and anthocyanins found in cranberries.
A diet high in antioxidants may reduce the risk of many diseases including heart disease and certain cancers. Antioxidants scavenge free radicals from the body cells and prevent or reduce the damage caused by oxidation.
The protective effect of antioxidants continues to be studied around the world. For instance, men who eat plenty of the antioxidant lycopene found in red fruits and vegetables such as tomatoes, apricots, pink grapefruit and watermelon may be less likely than other men to develop prostate cancer.
Lycopene has also been linked to reduced risk of developing type 2 diabetes mellitus. Lutein, found in spinach and corn, has been linked to a lower incidence of eye lens degeneration and associated vision loss in the elderly.
Research also suggests that dietary lutein may improve memory and prevent cognitive decline. Studies show that flavonoid-rich foods prevent some diseases, including metabolic-related diseases and cancer.
Apples, grapes, citrus fruits, berries, tea, onions, olive oil and red wine are the most common sources of flavonoids. Plant foods are rich sources of antioxidants.
They are most abundant in fruits and vegetables, as well as other foods including nuts, wholegrains and some meats, poultry and fish.
Good sources of specific antioxidants include:. There is increasing evidence that antioxidants are more effective when obtained from whole foods, rather than isolated from a food and presented in tablet form.
Research shows that some vitamin supplements can increase our cancer risk. For example, vitamin A beta-carotene has been associated with a reduced risk of certain cancers, but an increase in others — such as lung cancer in smokers if vitamin A is purified from foodstuffs.
A study examining the effects of vitamin E found that it did not offer the same benefits when taken as a supplement. A well-balanced diet, which includes consuming antioxidants from whole foods, is best. If you need to take a supplement, seek advice from your doctor or dietitian and choose supplements that contain all nutrients at the recommended levels.
Research is divided over whether antioxidant supplements offer the same health benefits as antioxidants in foods. To achieve a healthy and well-balanced diet , it is recommended we eat a wide variety from the main 5 food groups every day:.
To meet your nutritional needs, as a minimum try to consume a serve of fruit and vegetables daily. Although serving sizes vary depending on gender, age and stage of life, this is roughly a medium-sized piece of fruit or a half-cup of cooked vegetables.
The Australian Dietary Guidelines External Link has more information on recommended servings and portions for specific ages, life stage and gender. It is also thought antioxidants and other protective constituents from vegetables, legumes and fruit need to be consumed regularly from early life to be effective.
See your doctor or dietitian for advice. This page has been produced in consultation with and approved by:. Learn all about alcohol - includes standard drink size, health risks and effects, how to keep track of your drinking, binge drinking, how long it takes to leave the body, tips to lower intake.
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