During normal cell & tissue functions, including inflammatory processes, substances called "Free Radicals" (FR)  are produced as a natural byproduct of cell metabolism. Too many FR are not desirable as they can cause unwanted damage to cells & tissues. FR attack other cells, damage the cell membranes, damage proteins & damage cell DNA.
FR and immune dysfunction are the major causes of age related diseases so the maintenance of antioxidants and immune fitness is vital in the ageing animal.
When pets are sick, elderly, exposed to toxins, or suffer from poor nutrition or chronic diseases, excess FR can be produced. Chronic Dermatitis (skin conditions) & Arthritis are common diseases where ongoing inflammation can result in excess FR production. Our pets can be easily exposed to environmental toxins e.g. lawn fertilizers, licking floors, and even chemicals in bedding. Damage to cell DNA may result in cancer,
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"Antioxidants" (AO) are molecules that attack these destructive FR and safely remove them from the body. Our pets' own body has their own supply of AO but in pets with chronic disease & geriatric pets, these supplies can be depleted. 
​The geriatric animal's immune system is less able to efficiently fight disease and less able to mount a proper response to vaccinations. Therefore with a diet rich in antioxidants, the animal's immune system is better equipped to fight disease and illness.
Read more about ANTIOXIDANTS