As we have seen, antioxidant studies in humans have produced conflicting results. While it is apparent they play a vital role in the biology of life, their ability to improve our health and prolong our life has yet to be proven beyond a shadow of a doubt. Health professionals have not reached a unified consensus about what to recommend to their patients, and public perceptions of antioxidants, while clearly more positive and trusting, pose serious safety concerns. What we do know is that there are many synergistic interactions between compounds within the food matrix, bodily enzymes and hormones, and antioxidants themselves. It may very well be these synergies that account for the health benefits we attribute to antioxidants alone.
There are a number of biological substances and compounds that exhibit antioxidant activity. Some are exogenous vitamins, some are endogenous enzymes, some are mineral cofactors, and some exert their effects by modulating endogenous oxidative defense mechanisms. Confusion about what represents a "true" antioxidant is exhibited by the case of the mineral selenium. Even though it is considered an "antioxidant," selenium is actually an essential dietary micronutrient that is incorporated into selenoproteins. Selenoproteins are proteins that exhibit antioxidant characteristics, thereby giving selenium antioxidant status. Antioxidants can be classified into two groups: endogenous and exogenous.
Superoxide dismutase Glutathione peroxidase Ubiquinone (Co-enzyme Q10) Thioredoxin reductase Catalase
Vitamin C Vitamin E Carotenoids Selenium Polyphenols
Like vitamins, they are either water soluble or fat soluble. The water-soluble antioxidants react with oxidants in cell cytoplasm and blood plasma. The fat-soluble antioxidants protect cell membranes from lipid peroxidation. Antioxidant interactions between each other, enzymes, or metabolites affect how they function in the human body and antioxidant protection depends upon synergies, body concentration, and reactivity with free radicals they encounter. We have looked at the endogenous antioxidant in a previous chapter and will now focus on the exogenous antioxidant for the remainder of this chapter.
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