As the name suggests, antioxidants are substances that can resist harmful substances and normalize the physiological oxidation process of animal tissues. Antioxidants contain nutrients (vitamins and minerals) and enzymes (proteins in the body that assist in chemical reactions). These antioxidants are thought to play a role in preventing chronic diseases such as cancer, heart disease, stroke, Alzheimer's disease, rheumatoid arthritis, and cataracts.
Oxidative stress occurs when the production of harmful molecules (i.e., free radicals) exceeds the protective capabilities of antioxidants. Free radicals are chemically reactive atoms or molecular fragments that are charged due to excess or lack of electrons. For example, peroxide anions, hydroxyl groups, transition metals such as iron and copper, nitrate, and ozone are all free radicals. From a biological perspective, oxygen-containing free radicals, namely reactive oxygen species (ROS), are the most important free radicals. Reactive oxygen species include peroxide groups, hydroxyl groups, and oxygen-containing derivatives containing unpaired electrons, such as hydrogen peroxide, singlet oxygen, and hypochlorous acid.
Because free radicals contain one or more unpaired electrons, they are chemically very reactive. They move around in the human body to acquire or emit electrons, thereby damaging human cells, proteins and DNA (genetic material). This oxidation process can also cause oils to go rancid, peeled apples to turn brown, and iron to rust.
We cannot avoid the damage caused by free radicals. Free radicals can come from inside the human body (endogenous free radicals) or from outside the human body (exogenous free radicals). Oxidants inside the human body are produced by the body's aerobic respiration, metabolism, inflammation, etc. Exogenous free radicals are generated from various environmental factors, such as pollution, sunlight, strenuous exercise, X-rays, smoking, and alcohol consumption. The human body's antioxidant system is not perfect. As we age, cells damaged by oxidation will continue to accumulate.
Antioxidants prevent oxidative reactions by neutralizing free radicals. During this process, the antioxidants themselves will be oxidized. Therefore, the human body needs to continuously replenish nutrients containing antioxidants.
The mode of action of antioxidants can be divided into the following two types:
Chain scission type - after a free radical releases or acquires an electron, another free radical is produced. The molecule then repeats the same process with a third molecule, continually producing more unstable free radicals. This process will continue until the following conditions occur: the free radicals are stabilized by chain-breaking antioxidants such as β-carotene, vitamins C and E, or the free radicals lose or gain electrons and become neutral.
Preventive type - antioxidant enzymes (such as superoxide dismutase, catalase and glutathione peroxidase, etc.) prevent oxidation by reducing the chain initiation reaction rate. That is, these antioxidants prevent the oxidation chain from starting by scavenging initiating radicals in the body. They also prevent oxidation by stabilizing transition metal ions such as copper and iron ions.
The effectiveness of antioxidants in the body depends on the type of free radical, how and where it is generated, and where the damage occurs. Therefore, antioxidants may be effective against free radicals in some systems but completely ineffective in others. In some environments, antioxidants may even act as "pro-oxidants," producing toxic oxygen-containing species.
Antioxidant nutrients
The antioxidants we consume in our diet play an important role in controlling damage caused by free radicals. Each nutrient has its own unique structure and antioxidant function.
Vitamin E is actually a general term that refers to all substances that exhibit the biological activity of tocopherol isomers (an isomer is one of two or more molecules with the same chemical formula but different atomic arrangements) (which have so far been 8 species were found). α-Tocopherol is the most widely used isomer, with the highest biological efficacy and the strongest effect on the human body. Because it is soluble in fat (and only fat), alpha-tocopherol has the unique effect of protecting cell membranes (which are mainly made of fatty acids) from free radical damage. At the same time, alpha-tocopherol also prevents low-density lipoprotein (LDL or "bad" cholesterol) from being oxidized.
Vitamin C, also known as ascorbic acid, is a water-soluble vitamin. It scavenges free radicals in the water environment, such as those within cells. Vitamin C and vitamin E work side by side to eliminate free radicals. Vitamin C can also regenerate reduced (stabilized) vitamin E.
Beta-carotene, also known as a water-soluble vitamin, is the most widely studied of the 600 carotenoids discovered so far. Scientists believe that it is the best weapon to eliminate singlet oxygen (an uncharged reactive oxygen species that is harmful to cells). Additionally, beta-carotene is extremely effective at scavenging free radicals in low-oxygen environments.
Selenium is a trace element. Although the human body requires very little of this mineral, it is indispensable for human survival. It forms the active portion of certain antioxidant enzymes, including glutathione peroxidase.
The minerals manganese and zinc are also trace elements and are indispensable elements for various antioxidant enzymes.
Antioxidant enzymes
AntioxidantSuperoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) among chemical enzymes are the main lines of defense in the human body for destroying free radicals.
Superoxide dismutase first reduces the superoxide radical (O2-) (adds an electron to the superoxide radical) to generate hydrogen peroxide (H2O2) and oxygen (O2).
2O2- + 2H -- SOD --> H2O2 + O2
Then, catalase and glutathione peroxidase work with the protein glutathione at the same time to reduce hydrogen peroxide and finally generate water (H2O).
2H2O2 -- CAT --> H2O + O2
H2O2 + 2glutathione -- GPx --> oxidized glutathione + 2H2O
(The oxidized glutathione will then be reduced by another antioxidant enzyme-glutathione reductase.)
They work together to repair oxidized DNA, degrade oxidized proteins, and destroy oxidized lipids (fat-like substances that are components of cell membranes). Various other enzymes form a secondary line of antioxidant defense to prevent further damage to the body.
Other antioxidants
In addition to enzymes, vitamins and minerals, many other nutrients and compounds also have antioxidant properties. Among them, coenzyme Q10 (CoQ10, i.e. ubiquinone) is an essential element for energy production and can also prevent the human body from being damaged by free radicals. Uric acid is a product of DNA metabolism and has been widely recognized as an important antioxidant. In addition, there is a substance called phytochemicals in plants, and people are studying its antioxidant properties and "health-preserving" effects.
Some people may think that since antioxidants can eliminate the harmful effects of free radicals, taking more of them is better. In fact, while people rarely question the need for antioxidants to maintain health, it is less clear whether and how much antioxidant supplements should be taken. Previously, antioxidants were thought to be harmless to the human body. But now it's been discovered that antioxidants are potentially toxic and can interact with medications, so overdose may be harmful. Remember, overdosing on antioxidants can be counterproductive.
What is the basis for this statement? Many experimental (intervention) studies completed so far have produced a variety of results:
α-Vitamin E, β-carotene Cancer Prevention Study (ATBProject C) was tested on a number of Finnish male volunteers who were addicted to tobacco and alcohol. The volunteers were given 20 milligrams of synthetic beta-carotene, 50 milligrams of vitamin E, both, or just a placebo. After 8 years, men who took vitamin E had a 32% lower incidence of prostate cancer and a 41% lower mortality rate than those who did not. However, 4 years later, it was found that the incidence and mortality of lung cancer in men who only took beta-carotene were 16% and 14% higher than those who did not take it.
The Carotenoid and Retinol Efficacy Trial (CARET) project selected smokers or asbestos workers as test subjects. They received 30 milligrams of synthetic beta-carotene along with 25,000 international units (IU) of retinol (preformed vitamin A) or a placebo. Preliminary research showed that the incidence of lung cancer was 28% higher in those taking beta-carotene compared with those taking a placebo, so the study was stopped early.
The Physicians' Health Study (PHS), which involved 22,000 physicians (11% of whom were smokers and 40% had a history of smoking), showed that after 12 years of follow-up, researchers found neither beta-carotene nor beta-carotene. There was no protective effect and no toxic side effects were found. Participants were randomly selected and received 50 mg of beta-carotene or a placebo every other day. (The second Physicians' Health Study, currently underway, is examining whether beta-carotene, vitamin E, vitamin C, and a multivitamin containing folic acid contribute to cognitive decline in healthy men age 65 and older. Play a mitigating role)
A 1997 study published in the Journal of the American Medical Association showed that taking 60 mg of vitamin E daily can strengthen the immune system of healthy elderly people over 65 years old. Taking 200 mg daily for 4 months will improve the immune system by 4-6 times. However, if the study subjects took 800 milligrams of vitamin E per day, their immunity was reduced compared with those who did not take it.
In 2001, the medical community conducted a placebo-controlled clinical randomized trial, the Aged Eye Disease Study Trial (AREDS). Research shows that daily supplements of 500 mg of vitamin C, 400 IU of vitamin E, 15 mg of beta-carotene, 80 mg of zinc, and 2 mg of copper significantly reduce age-related macular degeneration (AMD) compared with placebo. ) incidence. Additionally, taking antioxidants plus zinc significantly reduced the prevalence of at least moderate eye disease.
There are several possible explanations for the above test results:
Antioxidant supplement doses may be higher than dietary intake, causing toxic side effects.
Fruits and vegetables may contain other nutrients that work with antioxidants to protect the body.
The study subjects may be too old to take antioxidants, or they may lead unhealthy lifestyles, so antioxidants cannot have beneficial effects.
Additionally, a large number of observational studies (which did not give participants antioxidant supplements because they were designed to find a relationship between antioxidants in food and human health) show that eating antioxidant-rich fruits and vegetables Helps reduce the incidence of cancer, heart disease, stroke, cataracts, Parkinson's disease, Alzheimer's disease, and arthritis. So even in the face of disappointing trial results, scientists still insist that dietary antioxidants have many potential benefits, but have not clearly defined how different antioxidant systems work together in the body to protect the body from free radicals. damage.
The American Heart Association recommends that people not take antioxidant supplements until "more comprehensive data are available," but recommends that "people eat a variety of foods from all basic diets every day." The Food and Nutrition Board of the American Medical Research Council is an advisory body affiliated with the National Academy of Sciences. The agency reported in April 2000 that vitamin C, vitamin E, selenium and carotenoids such as beta-carotene should be obtained from food and should not rely on supplements. After examining the available data on the health benefits and harms of antioxidants, the agency concluded that there is insufficient evidence that high intakes of antioxidants protect against chronic disease. In fact, the agency has warned that taking too much antioxidants can cause health problems, including diarrhea, bleeding and toxic reactions.
Since 1941, the U.S. Food and Nutrition Board has determined the types and amounts of nutrients needed for a healthy diet by referring to a large amount of scientific literature, repeatedly studying the principles of nutrients to prevent disease, and analyzing data on nutrient intake. For each category of nutrients, the committee defines reference dietary intakes (RDAs) and "tolerable upper intakes" (ULs) for nearly all healthy people (as a percentage of the total healthy population). 98% of the daily intake standard, while the tolerable maximum intake refers to the maximum amount that healthy people can take every day without negative effects. In some cases, the committee concluded there was insufficient evidence to determine how much of a particular nutrient was beneficial or harmful to health.
In recent years, the committee has been updating and expanding the system used to determine dietary nutrient intakes and tolerable maximum intake values, which are now collectively known as Dietary Reference Intakes (DRIs). 2000A published report "Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids" gives the recommended intake of antioxidants as follows:
Antioxidants
785 mg of synthetic vitamin E Excessive intake of vitamin E can damage blood coagulation function and increase the possibility of bleeding.
Men: 90 mg
Although research on nutrients containing antioxidants, especially vitamin E, is promising, it’s still wise to get your antioxidants from food. Research continues to prove that to maintain good health, it's best to consume 5 servings of fruits and vegetables a day as part of a balanced diet. Foods containing antioxidants are listed below. If you want to take antioxidant supplements, talk to your doctor about which supplement is best for you.
Vitamin E is found in vegetable oils, walnuts, peanuts, almonds, seeds, olives, avocados, wheat germ, animal liver and green leafy vegetables.
Photo courtesy of the United States Department of Agriculture
Citrus fruits (such as oranges and grapefruits), broccoli, green leafy vegetables, tomatoes, peppers, potatoes, melons and strawberries are rich in vitamin C.
Photo courtesy of the United States Department of Agriculture
Foods containing beta-carotene include melon, mango, papaya, pumpkin, pepper, spinach, kale, sweet potato and apricot.
Photo courtesy of the United States Department of Agriculture
Foods containing selenium include seafood, beef, pork, chicken, brazil nuts, brown rice and bran bread.
Photo courtesy of the United States Department of Agriculture
There are many substances containing phytochemicals. Scientists are currently studying the antioxidant properties and disease risk-reducing functions of some phytochemicals. These phytochemicals are listed below:
Phytochemicals
Of course, in addition to eating enough fruits and vegetables, a healthy lifestyle requires regular exercise and staying away from tobacco.