Antioxidants and Free Radicals: How Enemies Have Become Friends
Antioxidant means anti-oxygen. Our life is full of paradoxes. We cannot live without oxygen. But it is the oxygen that launches the oxidation processes, destroying cells and finally aging and death.
How did the standoff begin?
People have early detected that air has a destructive effect. At first, no one related this phenomenon and the impact of oxygen on health issues. It should be noted that iron gets rusty, wine sours, and fats become yellow and rancid. The solution for inanimate objects was pretty simple, restrict exposure to air, and that’s all.
During the XIX century, after the development of colonial trade, scientists focused on searching for substances that could prevent oxidation and food spoilage during long transportation. They were looking for food preservatives. And they have finally concluded that these should be antioxidants — substances that neutralize too active oxidation.
Since ancient times people have used vinegar and olive oil as preservatives. This is where the scientists tried to find “that very substance.” During the early 30s of the last century, they discovered and started to produce ascorbic acid (vitamin C) and later, by the middle of the century, vitamin E. These were the first antioxidants.
In 1970, Linus Pauling, the Nobel Prize in Chemistry winner, published a report “Vitamin C and Evolution,” where he explained that a human being (as he cannot live without oxygen) needs substances that would take the hit from active oxygen.
In the same year, the American gerontologist Denham Harman published a series of reports on his experiments with mice. It turned out that the average life expectancy increased if they were fed with food preservatives.
This is how the free-radical theory of aging started, which launched studies of antioxidants in medicine.
Theories of aging
Active forms of oxygen cannot exist by themselves. They are continuously interacting with something, breaking other molecular bonds. This creates free radicals, which also search for a place to become a part of. In fact, this is one of the strongest immune mechanisms: free radicals stick to microbes, which enter the human body and destroy them. But if there are too many free radicals, they start to destroy the body’s own cells. This is precisely how the aging process works, according to the research “Impact of Antioxidants on Cardiolipin Oxidation in Liposomes: Why Mitochondrial Cardiolipin Serves as an Apoptotic Signal?”
This is why, in the beginning, Harman titled his theory the “free radical theory.” According to this theory, the antioxidants coming from food could become a cure-it-all solution as they bond free radicals and get excreted from the body. Alternatively, they would slow down the activity of radicals, which would keep the cells eternally young.
However, soon it turned out that everything has its limits and that it is impossible to prolong life to eternity with the help of antioxidants. According to the research “Oxidative Stress: Harms and Benefits for Human Health,” active oxygen is accumulated in the human body even if the human lives in an ideal ecological environment. This can become the cause of developing cancer, diabetes, atherosclerosis, and cardiovascular diseases.
Harman expressed the idea that mitochondria (a power center of a live cell) launch the oxidation process by themselves. The pill of vitamin C and vitamin E can fight off free radicals coming to the human body from the environment, but they can do nothing about those produced in mitochondria.
This is how the mitochondrial theory of aging started (and it remains a leading one in gerontology) while humanity is looking for new types of antioxidants.
Classification of antioxidants
So far, antioxidants were classified into two big groups: endogenous (produced by the human body) and exogenous (which we receive from food, food additives, or cosmetics).
The primary source of endogenous antioxidants is in plants. The research “Natural Antioxidants in Foods and Medicinal Plants: Extraction, Assessment and Resources” sets aside the following main ones:
- Vitamins: С, Е
- Carotenoids: beta-carotene, lutein, lycopene, zeaxanthin, neoxanthin
- Polyphenols: phenolic acids, flavonoids, anthocyanins, tannins, stilbenes.
We can receive exogenous antioxidants following the recommendation of the WHO to take five servings of vegetables and fruits per day. Polyphenols are contained in all vegetables and fruits as well as in tea, coffee, and red wine.
Exogenous antioxidants help fight off external threats (bad ecology, sun radiation, smoking), but they cannot help with mitochondrial oxidation. Therefore, scientists started to look for ways to make the human body produce endogenous antioxidants “on request.” This is how the search for pro-antioxidants, substances which could stimulate the production of endogenous antioxidants, has begun. And according to the latest research, compiled in the report “The antioxidants and pro-antioxidants network: an overview,” there are many discoveries to make in this field.
What do prooxidants do?
Prooxidants act oppositely compared to antioxidants. Instead of neutralizing free radicals, they contribute to their formation.
They do so by “stealing” electrons from cells of our body, which makes them unstable. This creates a vicious chain reaction: the cell deprived of an electron does the same to a cell next to it to restore its own stability. This leads to damaging cells and their DNA.
And here, the paradox begins. Prooxidants turn out to be useful for our health. The research “Oxidative Stress, Prooxidants, and Antioxidants: The Interplay” has shown that the immune system increases its output to kill pathogens in the human body. Phagocytic cells increase oxygen intake by twenty times to generate more active forms of oxygen (free radicals) to kill viruses and bacteria. The prooxidants target not all cells but only those less stable and irregular. As a result, they make them self-destruct. Thus the enemy has become a friend!
Besides, prooxidants can interact with antioxidants, as well. For example, the research “Hydroxycobalamin catalyzes the oxidation of diethyldithiocarbamate and increases its cytotoxicity independently” has shown that vitamin B12 can transform other natural antioxidants, in particular, vitamin C and substances belonging to a group of theins (caffeine), into prooxidants.
Where to look for prooxidants
Among generally available prooxidants, one can mention:
- Vitamins: В3, В6, В12, contained in sardines, Atlantic mackerel, salmon, cottage cheese, and eggs.
- Omega-3 fatty acids can be found in cod liver, anchovy, linseed oil, nuts, or food additives.
- Amino acids: taurine, L-arginine, N-acetylcysteine, and glycine, which can be found in turkey, chicken, sunflower and pumpkin seeds, sesame, rough rice, and Brussels sprouts.
Researchers are closely studying the prooxidant role of minerals, including zinc, copper, and iron, but clinical research is not yet complete. Therefore, it is still too early to make conclusions. Science continues to advance, and since we already can neutralize harmful radicals and transform harmful components into useful ones, we have grounds for optimism in the future. Who knows, maybe they will soon find the longevity pill?
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