Antioxidants

Antioxidants are naturally occurring or synthetic substances that help protect the body’s cells from damage caused by free radicals — unstable molecules produced during normal metabolic processes and in response to environmental stressors such as pollution, ultraviolet radiation, and smoking. Free radicals can cause oxidative stress, leading to cell damage, ageing, and the development of chronic diseases such as cancer, diabetes, and cardiovascular disorders.
Antioxidants act by neutralising free radicals, thereby preventing them from causing harm to tissues, proteins, DNA, and cell membranes. They play a crucial role in maintaining cellular health, slowing down the ageing process, and supporting the body’s immune system.

Nature of Free Radicals and Oxidative Stress

Free radicals are molecules or atoms with one or more unpaired electrons, making them highly reactive and unstable. They are generated both endogenously (within the body) and exogenously (from external sources).
Sources of Free Radicals:

• Endogenous: Cellular respiration, immune responses, inflammation, enzymatic reactions.
• Exogenous: Air pollution, cigarette smoke, radiation, pesticides, and certain drugs.

When the production of free radicals exceeds the body’s capacity to neutralise them through antioxidants, it results in oxidative stress, which damages lipids, proteins, and nucleic acids, contributing to several degenerative diseases.

Mechanism of Action of Antioxidants

Antioxidants neutralise free radicals by donating electrons or hydrogen atoms without becoming destabilised themselves. This stabilises the reactive species and terminates the chain reaction of oxidative damage.
There are two major modes of antioxidant action:

1. Preventive Action:
   • Prevents formation of free radicals by inhibiting enzymes or chelating metal ions involved in oxidative reactions (e.g., catalase, glutathione peroxidase).
2. Chain-Breaking Action:
   • Interrupts the propagation of free radical reactions by donating electrons or hydrogen atoms (e.g., Vitamin E, Vitamin C).

Types of Antioxidants

Antioxidants are broadly classified into enzymatic and non-enzymatic types, depending on their origin and mechanism.

1. Enzymatic Antioxidants

These are endogenous enzymes produced by the body that catalyse reactions to convert free radicals into less harmful compounds.
Major Enzymatic Antioxidants:

These enzymes act synergistically to prevent oxidative damage at the cellular level.

2. Non-Enzymatic Antioxidants

These are dietary antioxidants obtained mainly from food sources, including vitamins, minerals, and plant-derived compounds.
(a) Vitamins:

• Vitamin E (Tocopherol): Fat-soluble antioxidant that protects cell membranes from lipid peroxidation. Found in nuts, seeds, and vegetable oils.
• Vitamin C (Ascorbic Acid): Water-soluble antioxidant that scavenges free radicals in blood plasma and regenerates Vitamin E. Found in citrus fruits, guava, and broccoli.
• Vitamin A (Retinol) and Beta-Carotene: Prevent oxidative damage to vision cells and skin tissues.

(b) Minerals:

• Selenium: Essential component of glutathione peroxidase, supports enzyme-based antioxidant systems.
• Zinc and Copper: Act as cofactors for superoxide dismutase.
• Manganese: Involved in mitochondrial antioxidant defence.

(c) Phytochemicals (Plant-based Compounds):

• Flavonoids: Found in tea, cocoa, fruits, and vegetables; known for anti-inflammatory and anti-cancer properties.
• Polyphenols: Found in berries, red wine, and olive oil.
• Lycopene: A carotenoid found in tomatoes, acts as a powerful antioxidant against lipid oxidation.
• Curcumin: Active component of turmeric with strong antioxidant and anti-inflammatory effects.

(d) Other Non-enzymatic Antioxidants:

• Uric acid, bilirubin, and albumin also act as natural scavengers of reactive oxygen species (ROS) in the body.

Sources of Antioxidants

Natural Food Sources:

Diets rich in fresh fruits, vegetables, and whole grains naturally provide a wide range of antioxidants, helping to maintain good health and prevent chronic diseases.

Role of Antioxidants in Human Health

1. Protection Against Chronic Diseases:
   • Antioxidants reduce oxidative damage linked to cardiovascular disease, diabetes, cancer, and neurodegenerative disorders (e.g., Alzheimer’s and Parkinson’s diseases).
2. Anti-Ageing Effects:
   • Delay ageing by protecting skin, tissues, and DNA from oxidative damage.
3. Boosting Immune Function:
   • Help in the regeneration of immune cells and support defence mechanisms.
4. Anti-Inflammatory Properties:
   • Prevent oxidative stress-induced inflammation, reducing the risk of metabolic disorders.
5. Eye and Skin Health:
   • Carotenoids like lutein and zeaxanthin protect against cataracts and macular degeneration.
6. Detoxification:
   • Glutathione and related antioxidants aid in the detoxification of harmful substances in the liver.

Oxidative Stress and Disease Link

• Cardiovascular Disease: Oxidative stress damages arterial walls and contributes to atherosclerosis.
• Cancer: DNA mutations from free radicals can trigger tumour formation.
• Diabetes: Excess glucose generates ROS, impairing insulin function.
• Neurodegeneration: Oxidative stress leads to neuronal cell death in Alzheimer’s and Parkinson’s diseases.

Synthetic and Industrial Antioxidants

In addition to natural sources, synthetic antioxidants are used in food preservation, pharmaceuticals, and cosmetics to prevent oxidation of fats and oils.
Common Synthetic Antioxidants:

• BHA (Butylated Hydroxyanisole)
• BHT (Butylated Hydroxytoluene)
• TBHQ (Tertiary Butylhydroquinone)

These are effective in preventing rancidity but are recommended in limited amounts due to potential health risks when consumed excessively.

Balance Between Oxidants and Antioxidants

While antioxidants are essential for health, excessive supplementation can disrupt the natural redox balance.

• Excessive intake of antioxidant supplements (e.g., high-dose Vitamin E or Beta-Carotene) has been linked to adverse effects in some studies.
• A balanced diet with diverse natural food sources provides sufficient antioxidants without harmful effects.