Antioxidants
Antioxidants are human made or natural substances that can prevent or delay some types of cell damage. A diet rich in vegetables and fruits, which are good sources of antioxidants, has been shown to be healthy, although research has not shown that antioxidant supplements are helpful in preventing disease. Examples of antioxidants are vitamins C and E, selenium and carotenoids such as beta-carotene, lycopene, lutein and zeaxanthin.
Main points:
a) Vegetables and fruits are a rich source of antioxidants. There is evidence that a diet high in vegetables and fruits is healthy, and the U.S. government encourages people to eat more of these foods. Research has shown that people who eat more vegetables and fruits have a lower risk of several diseases, although , it is not clear whether these results are related to the amount of antioxidants in vegetables and fruits, other components of these foods, other factors in people's diets, or lifestyle.
b) According to scientific studies of more than 100,000 people that investigated whether antioxidant supplements can help prevent chronic diseases such as cardiovascular disease, cancer, and cataracts, in most cases, antioxidants did not reduce the risk of developing these diseases.
c) High doses of antioxidant supplements may be associated with health risks in some cases. High-dose beta-carotene supplementation may increase the risk of lung cancer in smokers, and high-dose vitamin E supplementation may increase the risk of prostate cancer and stroke.
d) Antioxidant supplements may interact with some medications.
Free radicals, oxidative stress and antioxidants.
Free radicals are unstable molecules that are naturally produced during exercise and when your body converts food into energy. Your body can also be exposed to free radicals from various environmental sources, such as cigarette smoke, air pollution, and sunlight. Free radicals can cause "oxidative stress." , a process that can cause cell damage. Oxidative stress is believed to play a major role in a variety of diseases: cancer, cardiovascular disease, diabetes, Alzheimer's disease, Parkinson's disease, and eye diseases such as cataracts and age-related macular degeneration.
Antioxidant molecules have been shown to counteract oxidative stress in laboratory experiments (for example, in cell or animal studies), although it is debatable how beneficial it is to take large amounts of antioxidants in supplement form. There is also some thought that taking too many antioxidant supplements can be harmful.
Vegetables and fruits are healthy foods and rich sources of antioxidants. The US government encourages people to eat more vegetables and fruits. Concerns have not been raised about the safety of any amount of antioxidants in food.
Safety
High-dose antioxidant supplements can be harmful in some cases, for example, some studies have linked high-dose beta-carotene use to an increased risk of lung cancer in smokers, and high-dose vitamin E supplements to an increased risk of hemorrhagic stroke (a type of stroke caused by bleeding in the brain ) and prostate cancer.
Like some other dietary supplements, antioxidant supplements can interact with certain medications. For example, vitamin E supplements may increase the risk of bleeding in people taking anticoagulants (blood thinners). Some studies suggest that the effects of taking antioxidant supplements during cancer treatment may be beneficial, but others suggest that they may be harmful. The National Cancer Institute recommends that people being treated for cancer should talk to their doctor before taking antioxidant supplements.
Observational and laboratory studies
Looking at the typical eating habits, lifestyles, and health histories of large groups of people showed that those who ate more vegetables and fruits had a lower risk of several diseases, including cardiovascular disease, stroke, cancer, and cataracts. Observational studies can provide insights into possible associations between dietary or lifestyle factors and disease risk, but they cannot show which one factor causes the other because they cannot account for other factors, such as people eating more antioxidant-rich foods. They eat, they may exercise more and smoke less, and this is the reason for the lower risk of disease, not a large dose of antioxidants.Researchers have also studied antioxidants in laboratory experiments, showing that antioxidants interact with free radicals and stabilize them, thereby preventing free radicals from damaging cells.
Clinical researches of antioxidants
Because the results of such research looked so promising, large, long-term studies—many of which were funded by the National Institutes of Health—were conducted to test whether antioxidant supplements taken for at least a few years prevented cancer and cardiovascular disease. Reason for Avoidance In these studies, volunteers were randomly given either an antioxidant or a placebo (an identical-looking product that did not contain the antioxidant). The study was conducted in a double-blind fashion (neither the study participants nor the researchers knew which product they were receiving). These types of studies - called clinical trials - are designed to provide clear answers to specific questions about how a substance affects people's health.
The earliest of these studies was funded by the National Institutes of Health testing high-dose beta-carotene supplements, alone or in combination with other nutrients. These studies, completed in the mid-1990s, all showed that beta-carotene did not protect people from cancer or heart disease. - From vascular diseases. In one study, beta-carotene supplements increased the risk of developing lung cancer in smokers, while in another study, beta-carotene and vitamin A supplements had the same effect.
Recent studies have also found that in most cases antioxidant supplements do not help prevent disease. for example:
The Women's Health Study, which included 40,000 healthy women at least 45 years old, found that vitamin E supplements did not reduce the risk of heart attack, stroke, cancer, age-related macular degeneration, or cataracts. While the supplements were associated with a reduction in death from cardiovascular causes, they did not reduce the overall death rate of study participants.
b) The Women's Antioxidant Cardiovascular Study found no beneficial effect of vitamin C, vitamin E, and beta-carotene supplementation on cardiovascular disease (heart attack, stroke, or death from cardiovascular disease), diabetes, and cancer in 8,000 women over 40. in women who were at high risk of cardiovascular diseases. Antioxidant supplements also did not slow changes in cognitive function in women aged 65 and older.
c) The Physicians' Health Study II, which included more than 14,000 male physicians age 50 and older, found that neither vitamin E nor vitamin C supplementation reduced the risk of major cardiovascular disease (heart attack, stroke, or death from cardiovascular disease). - from vascular disease), cancer, or the probability of cataracts. In fact, in this study, vitamin E supplementation was associated with an increased risk of hemorrhagic stroke.
d) The Selenium and Vitamin E Cancer Prevention Study (SELECT) - a study of more than 35,000 men over the age of 50 found that selenium and vitamin E supplements, taken alone or together, did not prevent prostate cancer. A 2011 updated analysis concluded that vitamin E supplementation in men increased the incidence of prostate cancer by 17 percent. Prostate cancer did not increase when vitamin E and selenium were taken together.
In contrast to the studies described above, two large studies on age-related macular degeneration (AMD), the leading cause of vision loss in the elderly, showed a beneficial effect of supplements containing antioxidants. Both studies were funded by the National Institutes of Health.
A) The first study, called AREDS (Age-Related Eye Disease Study), showed that a combination of antioxidants (vitamin C, vitamin E, and beta-carotene) plus zinc and copper reduced the progression of intermediate AMD to advanced AMD by 25 percent over 5 years. During the period when this study was conducted, however, other studies showed that taking beta-carotene supplements increased the risk of lung cancer in people who smoked cigarettes.
b) A second study, called AREDS2 (Age-Related Eye Disease Study 2), showed that the carotenoids lutein and zeaxanthin are suitable replacements for beta-carotene in a supplement formula. Unlike beta-carotene, lutein and zeaxanthin did not increase the risk of lung cancer and 10% of study participants One-year follow-up data showed that lutein and zeaxanthin were more effective than beta-carotene in reducing the risk of AMD progression.
Why Antioxidant Supplements Don't Work?
Most clinical trials of antioxidant supplements have failed to show any health benefits. The researchers gave several reasons for this:
a) The beneficial effects of a diet rich in vegetables and fruits or other antioxidant-rich foods on health may be due to other substances in the same foods or to a different lifestyle.
b) The effects of large doses of antioxidants used in supplementation studies may differ from those of small amounts of antioxidants consumed in food.
c) Differences in the chemical composition of antioxidants in food compared to supplements can affect their effect, for example, eight chemical forms of vitamin E are found in food, on the other hand, vitamin E supplements usually include only one form - alpha-tocopherol. Alpha-tocopherol was also used in almost all vitamin E studies.
d) For some diseases, specific antioxidants may be more effective than previously tested, for example, to prevent eye diseases, antioxidants present in the eye, such as lutein, may be more useful than those not present in the eye, such as beta-carotene.
e) The relationship between free radicals and health may be more complex than previously thought. In some cases, free radicals can actually be more beneficial than harmful, and getting rid of them is undesirable.
f) Antioxidant supplements may not have been studied long enough to prevent chronic diseases such as cardiovascular disease or cancer that develop over decades.
g) Participants in the clinical trials discussed above were either members of the general population or people who were at high risk of specific diseases. They were not necessarily under increased oxidative stress. Antioxidants may help prevent disease in people who are under increased oxidative stress.
If you are considering taking antioxidant supplements
a) Do not use antioxidant supplements as a substitute for a healthy diet or conventional medical care.
b) If you have age-related macular degeneration, consult your doctor to determine whether supplements of the type used in the AREDS study are appropriate for you.
c) If you are considering a dietary supplement, first get information about it from reliable sources. Be aware that dietary supplements may interact with medications or other supplements and may contain ingredients that are not listed on the label. If you are pregnant or nursing, or if you are thinking about giving your baby a dietary supplement, it is especially important to consult your (or your child's) doctor.
d) Tell all your doctors about the complementary health approach you are using. Give him the full picture of what you are doing to manage your health. This will help ensure coordinated and safe care.
NCCIH- and NIH-funded research
Recent NCCIH research topics on antioxidants include:
A) Effects of two chemical forms of vitamin E on inflammation.
b) biological effect of selenium on immune function.
c) The effect of alpha-lipoic acid dosage spectrum on oxidative stress.
d) Effects of alpha-lipoic acid and acetyl-L-carnitine on inflammation in people with sickle cell disease.
NCCIH also sponsors the Center of Excellence for Antioxidant Therapy Research, which conducts research on the effects of antioxidants on various diseases and aging.
Other NIH components also fund antioxidant research. Recent topics include:
A) the effect of antioxidant therapy in Alzheimer's disease
b) The role of oxidation and antioxidants in relation to the risk of breast cancer.
c) Can pomegranate antioxidants help men reduce or treat prostate cancer?
d) Can anthocyanins (a group of antioxidants in berries) help people prevent esophageal cancer?
