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Free radicals are generated by exposure to harmful environmental factors, such as: smog, ozone, chemicals, drugs, smoking and radiation, as well as during normal physiological processes, especially in defense against microbes and other foreign substances. Free radicals can damage DNA, proteins and lipids within cells, altering or inhibiting cellular function. Dietary antioxidants, such as vitamins E and C, carotenoids and others, function to help control or eliminate free radicals by donating electrons, thus, maintaining cellular health by offsetting the damage they can potentially cause. Antioxidants that are available through the diet are considered exogenous antioxidants and include: amino acids [N-acetyl-L-cysteine (NAC), taurine and L-glutathione (tripeptide)], vitamins C and E, carotenoids (beta-carotene, lycopene, lutein and zeaxanthin), and minerals (selenium and zinc). Antioxidants produced in the body are considered endogenous antioxidants and include: ubiquinone/ubiquinol (CoQ10), alpha lipoic acid and the master cellular defense enzyme, superoxide dismutase (SOD) and many more. However, many factors have been found to compromise the levels of endogenous antioxidants in the body making supplementation essential, such as the normal aging process, certain medications and oxidative stress.
Exogenous Antioxidants
Carotenoids (or carotenes) (or carotenes) and other colorful compounds are abound in the plant kingdom. They are highly pigmented (red, orange, yellow), fat-soluble compounds naturally present in many fruits, grains, oils and vegetables (green plants, carrots, sweet potatoes, squash, spinach, apricots and green peppers). Plants produce these compounds to attract insects for pollination and animals for seed distribution. These compounds also protect the plants from UV light, acting as a natural sunscreen. Carotenoids also play an important role in human health by acting as antioxidants, protecting cells and tissues from the damaging effects of free radicals.
Alpha, beta, and gamma carotene are the most popular carotenoids and are considered provitamins because they can be converted to active vitamin A. Lycopene, the hydrocarbon carotenoid that gives tomatoes their red color, is particularly effective in preventing cell damage from dangerous free radicals. Clinical studies have shown that lycopene most notably supports prostate health, but it also maintains heart, eye and skin health. Lutein, zeaxanthin and xanthophylls (or yellow pigments) found in corn and in leafy greens, such as kale and spinach, are believed to function as protective antioxidants in the macular region of the human retina. Zeaxanthin protects the eyes by absorbing destructive blue light and reducing glare. Aside from positively supporting eye health, lutein also plays a key role in maintaining skin and cardiovascular health. 
Polyphenols represent a very broad category of plant compounds that include simple phenolics, as well as highly polymerized compounds, such as tannins. The one common feature that brings this diverse group together (>8,000 different compounds) is their antioxidant potential to scavenge or neutralize free radicals in the body for optimal health and well-being. Bioflavonoids or flavonoids are the most well-known subclass of polyphenols. Common bioflavonoid subclasses are flavones (e.g., apigenin and luteolin), flavonols (e.g., quercetin, kaempferol and myricetin), isoflavones (e.g., genistein, daidzein and glabridin), flavanols (e.g., gallic acids, catechins, EGCG and GC), flavanones (e.g., naringenin), glycosides (derivatives of the parent compound) and proanthocyanidins/anthocyanidins (e.g., phytonutrients commonly found in red wine and grape seed extracts, as well as in some fruits and vegetables that are typical within the Mediterranean diet, which have been long known for their capillary and cardio protective effects). Bioflavonoids are typically derived from citrus fruits that work synergistically with vitamin C and other antioxidants to offer the immune system extra protection. Bioflavonoids also help maintain the walls of small blood vessels, allowing for healthy circulation.