Background information

Free radicals, oxidative stress and antioxidants

Free radicals are produced during metabolism of food and exercise. Radiation (dental X-ray and sunlight), toxins from food, and pollutants in the environment also contribute free radicals. Free radicals are highly reactive oxygen species (ROS) or reactive nitrogen species (RNS) that can induce oxidative damage on cellular components (proteins, DNA and lipids). Damage of these cellular components leads to inflammation and results in degenerative diseases. Damage to DNA will lead to cancer cell formation and spreading. Our bodies have endogenous enzyme systems and antioxidants (glutathione, uric acid and coenzyme Q) to deal with these free radicals. Antioxidants can also be obtained from the food we eat, such as beta-carotene, vitamin C, vitamin E, selenium, and polyphenols. The antioxidants can: (1) scavenge the free radicals; (2) inhibit the enzymes that generate free radicals; (3) up-regulate the antioxidant defense system; (4) inhibit enzymes that catalyze oxidation of cellular components; or (5) chelate transition metal ions responsible for generation of free radicals. In young and healthy individuals, the production and removal of free radicals are well-regulated. Due to aging or poor diet, antioxidant levels in the body will be lower, and can no longer counteract the free radicals. This condition is known as oxidative stress. Prolonged oxidative stress can cause cellular damages, leading to a variety of age-related diseases, such as cancer, cardiovascular diseases, type-2 diabetes, Alzheimer’s disease, Parkinson’s disease, cataract and macular degeneration.  Increased intake of antioxidants from food or supplements may help to mitigate the oxidative stress and slow down the manifestation of these diseases.

Health benefits of antioxidant supplements

Since antioxidants can mitigate oxidative stress which is the cause of many age-related diseases, it is believed that consumption of antioxidant supplements will be beneficial to health. Beneficial effects of antioxidants have been demonstrated in experiments using cell cultures and animal models.  However, these have not been confirmed by clinical studies. On the contrary, some clinical studies have shown that antioxidants (vitamin C, vitamin E and beta-carotene) have no protective effect, and in some cases these supplements can increase risk of cancer in certain people. Just to be fair, these clinical trials used synthetic antioxidants in high doses. The failure of these clinical trials may be due to the following reasons: (1) optimal dose was not used; (2) the synthetic antioxidants used in these studies are in different chemical forms than those found in fruits and vegetables; and (3) the trials were not run long enough to see the positive effects. Therefore, people who are seeking antioxidant supplements for prevention of age-related diseases should not be discouraged by the lack of positive results of clinical trials.  Many antioxidants have not yet been tested in clinical trials due to the lack of research funding. Natural antioxidants extracted from fruits and other plant sources may help to prevent age-related diseases in people who do not have sufficient intake of antioxidants from their diet, such as the aging folks and picky eaters.

Should I take antioxidant supplements?

Fresh fruits and vegetables are good source of antioxidants. Some doctors claim that taking antioxidant supplements is a complete waste of money.  If you are young and are eating a variety of fruits and vegetables, especially those antioxidant-rich fruits, such as blueberries, raspberries, cranberries, black currant, pomegranate, plum, and acai berries, you probably need not take any antioxidant supplements. On the other hand, if you are aging, you may not get enough antioxidants from your diet alone due to poor digestion or absorption.  Antioxidant supplements from plant sources may be beneficial to your health.  However, antioxidant supplements should not be used to replace fresh fruits and vegetables, as the latter will provide other nutrients and fibers. You should avoid taking large amount of synthetic antioxidant vitamins, such as vitamins E and C.

Precautions in taking antioxidant supplements

In general, natural antioxidant supplements from plant sources are quite safe.  However, some antioxidant supplements may interact with certain medications. Consult your physician before taking these supplements. At low levels, free radicals are also used by your cells for fighting pathogens and other normal cellular signalling.  Free radicals have been shown to play a role in the extension of life span. Therefore, do not take larger doses of the supplements than those recommended. More of a good thing does not necessarily mean better. In fact, overdose of antioxidants may have the opposite effects. Some antioxidants may have pro-oxidant properties in large doses.  

Although research has shown that antioxidant supplements have the potential of preventing or slowing down the development of age-related diseases, they have not been approved for curing any disease.  Antioxidants can prevent further cellular damage by mitigating free radicals, but cannot reverse damages already done.  

Choosing an antioxidant supplement should not be based on price alone, as many supplements fail to deliver what they are claimed to contain. A reliable source of antioxidant supplements is shown at the sidebar, the products recommended there are known to be of high quality.

Antioxidant supplements and cancer

Antioxidants can mitigate free radicals, which damage DNA and cause gene mutation leading to the development of cancer.  Therefore, antioxidants supplements are good for cancer prevention.  However, cancer patients undergoing treatment should avoid taking antioxidant supplements. First, antioxidant can interfere with cancer therapy and decrease its efficacy, as chemotherapy and radiation therapy of cancer utilize free radicals to kill cancer cells. Some antioxidants are able to kill cancer cells or sensitize them to chemotherapeutic drugs or radiation in the laboratory, but their potential therapeutic applications are still controversial.  Second, cancer cells are known to have increased free radical levels as compared to normal cells, antioxidant will facilitate cancer cell survival by neutralizing the free radicals. Some antioxidants can actually speed up the growth and metastasis of some cancers.  Third, not all tumors will benefit from antioxidant treatment. There are a wide variety of cancers with different genetic defects and antioxidants with different mechanism of actions. It will be difficult to select the right antioxidant to treat a certain cancer. Furthermore, dose level is difficult to be determined because antioxidant can have pro-oxidant activities at high doses.

Types of antioxidants

Antioxidants are classified into several groups according to their chemical structures.  For a list of common antioxidants and their properties, please click on the “Types of Antioxidants” tab for more information.

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