Antioxidants

Figure 1. Chemical structure of gluthathione, an antioxidant.

Antioxidants are compounds that inhibit oxidation, a chemical reaction that can produce free radicals and chain reactions that may damage the cells of organisms. Oxidation is a natural phenomenon. While humans require oxygen to live, oxygen is a highly reactive element and can cause cellular damage via the production of reactive oxygen species. To balance this, organisms contain and produce antioxidants such as glutathione, mycothiol, or bacillithiol. In general, antioxidant systems either prevent these reactive oxygen species from being formed or remove them before they can damage vital components of the cell.

The reactive oxygen species produced in cells include hydrogen peroxide (H₂O₂), hypochlorous acid (HClO), and free radicals such as the hydroxyl radical (OH) and superoxide anion (O₂⁻). These oxidants damage cells by starting chemical chain reactions such as lipid peroxidation, or by oxidizing DNA or proteins. Damage to DNA can cause mutations and possibly cancer while damage to proteins causes enzyme inhibition, denaturation and protein degradation among other negative effects.

Given the highly reactive nature of the oxygen molecule, Antioxidants work to prevent or slow damage to cells caused by free radicals resulting from oxidation. Because of this, Antioxidants are also commonly called "free radical scavengers". Oxidation is not the only process that generates free radicals, as environmental and other pressures such as inflammation, pollution, exposure to UV rays, and cigarette smoke are all factors that lead to the production of free radicals. 

Food Sources

Antioxidants are classified into two broad categories based on whether they are water-soluble (hydrophilic) or lipid-soluble (lipophilic). Antioxidants may be synthesised in the body or obtained from dietary intake. Antioxidants produced by the body are known as endogenous antioxidants, whereas those that are consumed from outside the body are known as exogenous.

Sources of Antioxidants may include (but not limited to):

• Ascorbic Acid, i.e. Vitamin C
• Glutathione
• Lipoic Acid
• Uric Acid
• Carotenes
• Alpha-tocopherol, i.e. Vitamin E
• Ubiquinol, i.e. Coenzyme Q10
• Carotenoids, e.g. Beta-carotene
• Lycopene
• Lutein
• Selenium

Antioxidants are naturally found in vegetables, fruits, eggs, legumes, and nuts. They are good, natural, and healthy sources of Antioxidants. 

The effects of cooking and food processing are complex. On one hand, Vitamins A, C, and E can be destroyed by long-term storage or prolonged cooking. On the other, cooking can also increase the bioavailability of antioxidants, such as some carotenoids in vegetables. Generally speaking, processed food contains fewer antioxidant vitamins than fresh and uncooked foods, as preparation exposes food to heat and oxygen.

Natural food sources of Antioxidants include:

• Dairy produce, eggs, and liver (Vitamin A)
• Most fruits and vegetables (Vitamin C)
• Nuts and seeds, sunflower and other vegetable oils, and green, leafy vegetables (Vitamin E)
• Brightly colored fruits and vegetables, such as carrots, peas, spinach, and mangoes (Beta-carotene)
• Pink and red fruits and vegetables, including tomatoes and watermelon (Lycopene)
• Green leafy vegetables, corn, papaya, and oranges (Lutein)
• Rice, corn, wheat, and other whole grains, as well as nuts, eggs, cheese, and legumes (Selenium)
• Goji berries

Effects of Oxidative Stress

Oxidative stress occurs in the body when antioxidant systems fail to sufficiently prevent or remove reactive oxygen species from the body. Oxidative stress has been linked to heart disease, cancer, arthritis, stroke, respiratory diseases, immune deficiency, emphysema, Parkinson’s disease, and other inflammatory or ischemic conditions.

Side Effects

• A high intake of Beta-carotene has been linked to an increased risk of lung cancer in smokers.
• A high dose of Vitamin E has been found to increase the risk of prostate cancer.
• The use of some antioxidant supplements has been linked to a greater risk of tumour growth.
• Antioxidant supplements may also interact with some medications.