Antioxidants and cancer

DEFINITION: Antioxidants are a class of compounds that help prevent damage to deoxyribonucleic acid (DNA), cellular proteins, and cell membranes. They do this by combining with potentially damaging molecules called free radicals and neutralizing them. The body naturally makes many antioxidants, while others exist in fruits, vegetables, and grains. Herbs are also a rich source of antioxidants. Antioxidants are also produced synthetically as dietary supplements.

Cancers treated or prevented: As a disease, in 2023, cancer accounted for an estimated 10 million deaths worldwide deaths. Studies suggest this number will increase to 28.4 million, a rise of 47%, by 2040. The expected rise is largely attributed to increased aging and population growth. Thus, there is high global demand for cancer cures. Antioxidants are used to treat most types of cancer, although their effectiveness is questionable. They are usually taken for cancer prevention, although the link between antioxidant consumption and cancer prevention in humans is inconclusive.

Delivery routes: Oral, as tablets, caplets, capsules, powder, or tea; some fruits and vegetables are high in antioxidants

How these compounds work: Free radicals are formed during normal cellular metabolism. Free radicals are compounds that are unstable because they contain an unpaired electron. This unpaired electron causes the free radical to react with other molecules to gain another electron. This creates an electron pair and a more stable molecule. The process of gaining an electron is called oxidation. Antioxidants in the body react with free radicals, which makes them harmless to cells. Cells naturally make many antioxidants, such as glutathione and coenzyme Q10 (ubiquinone). When the number of free radicals exceeds the antioxidants available to neutralize them, however, the body develops a condition called oxidative stress. Oxidative stress makes cells especially susceptible to damage.

Free radical formation and oxidation are normal processes. Oxidation and oxidative stress, however, are thought to contribute to aging, as well as to cancer, cardiovascular disease, and other chronic diseases. Without adequate antioxidant compounds, free radicals most often combine with and damage DNA, cellular proteins, and molecules in cell membranes. This damage can cause gene mutations and change cellular metabolism, leading to cancer and other diseases. Exposure to ultraviolet (UV) light, radiation, cigarette smoke, and other known carcinogens increases the number of free radicals that are formed, suggesting another link between free radicals, oxidative stress, and cancer.

In theory, increasing the amount of antioxidants in the body should decrease the amount of damage to DNA and cells and reduce the risk of cancer. Antioxidants have been shown to prevent or slow the development of some cancers in cell cultures grown in the laboratory and in some animal studies. The results in human studies have been mixed. Despite claims by some manufacturers of antioxidant dietary supplements, no clear link between antioxidant consumption and cancer prevention or treatment has been established in humans. The role of antioxidants in preventing and treating cancer is of high interest to research scientists. Many clinical trials are being conducted, and there is no cost for qualified individuals to participate in a clinical trial.

The body makes some antioxidants, but others must be acquired through diet. Common antioxidants that the body does not make include vitamins A, C, and E, carotenoids, and flavonoids. Selenium is a mineral not strictly an antioxidant but essential to many antioxidant reactions. It is often classed with antioxidants. Coenzyme Q10 and glutathione are antioxidants naturally produced by the body that are also manufactured sold as high-dose supplements.

Vitamin A (retinol) is a fat-soluble vitamin found in liver, egg yolks, whole milk, and dairy products made with whole milk. It is also sold as a dietary supplement. It is included in most multivitamin tablets and in special antioxidant formulations such as ACE, a combination of vitamins A, C, and E. Vitamin A is essential to health. Still, its role in cancer prevention and treatment is unclear. All-trans-retinoic acid (ATRA, Vesanoid) is a pharmaceutical drug derivative of vitamin A. It is successfully used to treat promyelocytic leukemia and is being studied in individuals with breast and skin cancers. However, vitamin A alone has not shown the same cancer-reducing effects as ATRA.

Alpha-carotene, beta-carotene, beta-cryptoxanthin, lutein, zeaxanthin, and lycopene, all carotenoids, demonstrate antioxidant activity in laboratory tests. These compounds, found in red, yellow, and orange plants like carrots, cantaloupe, mango, and tomato, are also available as dietary supplements. In the body, carotenoids are converted into vitamin A. Notably, a recent examination of twenty-one studies on lycopene consumption and prostate cancer revealed that men with the highest lycopene intake experienced a modest decrease in the incidence of prostate cancer. This underscores the active and evolving role of carotenoids in cancer prevention research.

Vitamin C (ascorbic acid), a water-soluble vitamin found in citrus fruits, has a rich history in health. For centuries, it has been recognized as a crucial element in preventing the disease scurvy. While dietary supplements of vitamin C are often marketed as a preventive or treatment for the common cold, clinical studies have not yet proven its effectiveness in this regard. Vitamin C, with its potent antioxidant activities, has been the subject of multiple human studies, but a significant link between cancer prevention and vitamin C intake has not been established.

Vitamin E is a group of related compounds, the most active of which is alpha-tocopherol. Vitamin E is a fat-soluble vitamin with antioxidant properties. It is found in olive, sunflower, safflower oils, and many nuts. The role of vitamin E in cancer prevention is controversial. The National Institutes of Health reported in 2013 that the antioxidant qualities of vitamin E make it possible to block the formation of carcinogenic qualities of various foods and the damaging effects of free radicals. However, human trials and studies have not linked vitamin E intake with a reduction of cancer incidence. A 2014 study from the Public Health Sciences Division of the Fred Hutchinson Cancer Research Center elaborated on this by stating that high doses of the vitamin have the potential for a heightened risk of developing prostate cancer in some men.

Flavonoids are a group of antioxidant compounds found primarily in brewed tea, red wine, dark chocolate, apples, berries, and citrus fruits. These compounds have antioxidant activity. Traditional Chinese medicine has promoted the health effects of green tea for centuries, and recent studies show that dark (bitter) chocolate in small quantities may promote heart health, but the role of flavonoids in cancer prevention is unclear.

Selenium is a mineral found in fish, shellfish, grains, Brazil nuts, and many vegetables grown in selenium-rich soils. By itself, selenium is not an antioxidant, but it plays a critical role in antioxidant activity and is often classified with the antioxidants that must be acquired through diet. Selenium deficiency has been linked to increases in colorectal, lung, and prostate cancers. Increased selenium intake in people who are not selenium deficient, however, does not decrease the risk of developing cancer. Additionally, selenium is toxic in large doses.

Coenzyme Q10 and glutathione are the primary antioxidants made by the body. They are also sold as dietary supplements. Studies of individuals who supplemented their diet with synthetic coenzyme Q10 or glutathione found no evidence that these supplements protected against cancer.

Individuals who maintain a healthy weight and eat a diet low in fats and high in fruits, vegetables, and whole grains develop cancer at a lower rate than individuals who eat a more traditional American diet high in fat and low in fruits and vegetables. The American Cancer Society and the National Cancer Institute recommend that individuals meet as many of their vitamin, mineral, and antioxidant needs as possible by eating a healthy, varied diet rather than by taking dietary supplements.

In this regard, the consensus on the efficacy of antioxidant supplements is mixed at best. According to a 2023 study published in MDPI, antioxidant supplements, including vitamins A, C, and E, can help reduce the risks of certain types of cancers. Nonetheless, the same MDPI study acknowledges other research has indicated an increased risk of cancer from antioxidants. The reasons are not entirely known. Thus, as of mid-2020, more about antioxidant supplements needed to be understood before a consensus could be reached on their effectiveness as a preventative measure against cancer.

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