By Tracy Meyer-Wilson, nutritionist, Advit
Vitamin E is an effective anti-oxidant that helps to protect against disease. Due to the bioavailability being limited, it is one of the more expensive components in the diet. Polyphenols have been shown to not only partially replace vitamin E in the diet, but to potentially boost anti-oxidative defences beyond the capacity of vitamin E alone. Free radicals caused by oxidative stress are a natural result of daily metabolism.
An animal’s growth rate and health status will influence free radical production, for example, during periods of rapid growth there is a higher metabolic activity, resulting in an increased oxidative stress. When the animal has a health challenge, the immune system will generate additional free radicals to eliminate the bacteria or virus, again, increasing the oxidative stress. Free radicals can attack and damage cell membranes causing them to lose their fluidity, which affects nutrient transport. Proteins will lose their structure and their ability to catalyse reactions and DNA can be altered or broken, leading to translational errors.
There are two lines of defence in combating free radicals and preventing oxidative stress.Firstly, enzymes (catalase, superoxide dismutase and glutathione peroxidase) can convert free radicals into water and oxygen. The second line of defence is the anti-oxidants (vitamin E, vitamin C, lipoic acid and glutathione).
Vitamin E’s key feature is a benzene ring with a hydroxyl group attached.The electrons in this benzene ring are mobile which allows the hydrogen in the hydroxyl group to split off and neutralise the free radical.
Although the anti-oxidative function of Vitamin E is the most well-known, it has many biological functions (gene expression, enzymatic activity regulation and neurological functions). Nothing can replace vitamin E in this role.Vitamins E’s function as an anti-oxidant can be filled by other anti-oxidants, sometimes more effectively, providing they act in the same cellular location and with a similar affinity for free radicals. The synthetic vitamin E generally used in animal nutrition contains a blend of eight stereo-isomers of which only one is natural vitamin E with a good bioavailability.
The other seven stereo-isomers are not well recognised by the liver and are predominately returned to the gastro-intestinal tract.The actual bioavailability of synthetic vitamin E is 33% for pigs.The half-life also decreases with increased doses, which in simple terms means that increasing the vitamin E level in the diet will only improve availability up to an inflection point (half-life) at which point further increases will have no effect.
Polyphenols are plant compounds with an anti-oxidant potential.The basic structure of these compounds includes a phenol group, just like vitamin E.The anti-oxidant potential of polyphenols has been known for centuries.Within the polyphenols range there are compounds that have more hydroxyl groups attached to benzene rings per unit of weight than vitamin E, which means they have an even higher anti-oxidant potential. Not all polyphenols are suitable as one-on-one replacements for the anti-oxidant function of vitamin E. Bioavailability, radical affinity, tissue distribution and metabolism must all be considered.
Nutrition is advancing on a daily basis.Costs are increasing and alternative feed ingredients are becoming an important aspect of the diet.Polyphenols are the ideal anti-oxidant to include in the diet to replace the vitamin E anti-oxidative function.