The major sources of free radicals include:
Ordinary body functions, such as breathing and digestion
Exposure to radiation
Exposure to other environmental pollutants
Consumption of cigarettes or tobacco, drugs, and alcohol
Certain medications or high use of antibiotics, which leads to antibiotic resistance
A poor diet that includes foods like unhealthy fats (trans fats), too much sugar, pesticides, herbicides or synthetic additives. Many processed and refined foods contain oxidized fats that add free radicals to the body. Excessive amounts of sugar and sweeteners are other sources of free radical growth that contribute to aging, weight gain and inflammation.
Even too much exercise (overtraining) generates added free radicals
High amounts of emotional or physical stress.
Stress hormones (like too much cortisol) can generate free radicals.
Inside the body the radicals can attack cell membranes leading to wrinkles and skin diseases, such as eczema and psoriasis. Arterial walls become damaged, leading to the beginning of blocked arteries of atherosclerosis. Double bonds found in unsaturated fats (vegetable oils in cooking) and in DNA are attacked leading to an increased risk of cancer and arthritis. The damage caused by free radicals is also the major source of delayed muscle soreness, or DOMS, felt for several days after intense exercise. Links have also been made between free radicals and Alzheimer's disease, diabetes, hypertension, rheumatoid arthritis, mental illness and macular degeneration of the eye. On a positive note, free radicals are utilised by some cells within the immune system in order to kill harmful microbes.
Defence mechanism - Antioxidants: As the human body evolved to utilise oxygen, it has also evolved elaborate defences in order to limit free radical damage. These come in the form of antioxidant enzymes, which the body produces naturally within the cells, such as superoxide dismutase. Dietary antioxidants can also be acquired from the food that we eat. People with poor diets, depleted of nutrients, may be at greater risk, as the body's antioxidant enzymes require nutrients such as vitamins A, C, E and minerals including zinc, selenium, copper and manganese in order to function properly. Antioxidants are substances that slow oxidation by neutralising free radicals and work by being able to donate or receive electrons. Both the enzymes and the nutrients play a role in breaking the damaging chain reactions. Research suggests that regular exercisers do have a much higher level of their natural antioxidant enzymes to help protect them.