Oxidative Stress: Antioxidants in Competition with Free Radicals
Oxidative stress and cell damage caused by free radicals are often associated with all kinds of diseases, from arthritis to heart attacks and cancer. The natural antagonists of the harmful metabolic products are so-called antioxidants. Stress and radicals, that sounds dangerous - but why should antioxidants protect us from them? Follow us on a search for clues in the realm of biochemistry.
How does oxidative stress arise?
Most oxidative stress occurs during cellular respiration. This is the part of metabolism in which food components are converted into water, carbon dioxide and energy using oxygen from the air we breathe. The whole process is achieved through a system of many interconnected reactions, the so-called citric acid cycle. The individual reactions, like many other metabolic processes, are redox reactions. One substance is reduced while the other is oxidized. For chemists, oxidation means that a substance gives off an electron. During reduction, a substance absorbs an electron. This releases energy. Combustion is a typical redox reaction. If such a reaction were to be stopped at the moment of electron transfer, both reaction partners would be present as so-called radicals, since they have an unpaired electron at this point. In this state, atoms or molecules are very reactive and bind to the next possible reaction partner in order to regain a stable state. Once started, redox reactions continue until all reactants are used up.
Where in the cell does the redox reaction occur?
Cellular respiration takes place in almost every cell in the human body. Cells have tiny organelles responsible for this - the mitochondria. Since energy is produced there, they are often referred to as the power plants of the cells. The various reactions of the citric acid cycle take place alongside one another in a very small space - you may remember this from biology class. A system of cell membranes, enzymes and antioxidants stabilizes the individual reactions, comparable to a test tube in which only the right reaction partners are present. Sometimes, however, radicals overcome this protective system and then look for new reaction partners as free radicals. Since these are molecules with a charged oxygen particle, they are also referred to as reactive oxygen species or ROS (reactive oxygen species). Oxidative stress occurs when the formation of reactive oxygen species can no longer be compensated for by the protective systems.
How are free radicals formed?
Free radicals are created to a certain extent as part of the various metabolic processes. There they normally encounter a well-equipped protective system, which catches them again. However, unfavorable environmental influences can also lead to the formation of free radicals. This mainly affects environmental toxins that are inhaled through the air we breathe, such as exhaust fumes and tobacco smoke. However, one of the biggest factors in the formation of free radicals is UV radiation. This high-energy part of sunlight can split molecules into radicals, which can lead to damage to cell walls and can be noticed as sunburn, among other things. To counteract this unfavorable influence, the skin has its own protective system against UV radiation in the form of the pigment melanin. The macula, the visual center of our eye, also has its own system for protection against UV radiation. The macula is enriched with the two color pigments lutein and zeaxanthin , which, due to their structure, are able to absorb the particularly high-energy part of the light.
Diet and stress in the formation of free radicals
Our own lifestyle habits can also play a large role in the formation of free radicals. Important factors that almost everyone is familiar with from their everyday lives are stress and an unbalanced diet. Stress means that all internal systems are on alert. The body is always ready to flee or ward off danger. The mitochondria are working at full speed because energy must be provided permanently. This can lead to an unfavorable metabolic state in which the ROS can no longer be balanced out by the protective systems. Stress also often leads to unfavorable eating habits. Irregular meals consisting of fast food or pizza because it has to be quick and uncomplicated put additional strain on the body. Sugary and fatty foods in particular are suspected of promoting silent inflammation , which in turn can put the body on alert even without prior stress. A very one-sided diet that hardly uses any fresh fruit or vegetables can also throw the cellular protective system out of balance. This is because it consists largely of vital substances that must be ingested with food.
How does the body protect itself from free radicals?
The body has various repair systems at its disposal to protect itself from damage caused by free radicals. Cell walls are constantly regenerated and DNA is also equipped with a backup copy of itself thanks to its double helix structure. A complex system of different antioxidants is available to prevent damage from the outset. These include very different classes of substances, such as enzymes and hormones, but also substances that come directly from food, such as vitamins, trace elements and secondary plant substances. These are stored in greater quantities in the mitochondria, where particularly complex reactions take place with the citric acid cycle, and they also fulfil very different tasks there.
What different forms of antioxidants are there?
All substances that are able to support the metabolism in dealing with free radicals can in principle be referred to as antioxidants. For example, there are enzymes such as superoxide dismutases that are able to specifically convert superoxide radicals into the more stable hydrogen peroxide. They thus contribute to a controlled course of metabolic reactions. Vitamins A, C and E, as well as secondary plant substances such as carotenoids, flavonoids and anthocyanins (all plant pigments) are able to bind free radicals to themselves and thus render them harmless. Would you like another example? The coenzyme Q-10 is an electron carrier and is directly involved in part of the citric acid cycle, namely in the so-called oxidative phosphorylation. This substance can also render free radicals harmless. Paradoxically, Q-10 has both oxidative and antioxidant properties. The fatty acid alpha-lipoic acid is also part of the body's own protective system. It is able to reactivate bound antioxidants after they have been used up by taking over their bound radicals - like handing over a delinquent from the police to the justice system. It performs this feat with vitamin C, vitamin E, coenzyme Q10 and glutathione, for example. These are just a few examples of antioxidants and their potential function, and research in this area is far from complete.
How can I support my body's protective function?
The best protection against oxidative stress is to avoid everything that triggers oxidative stress - a banal but no less correct statement. This means above all that excessive UV radiation and environmental toxins should be avoided. Regular exercise contributes to a healthy lifestyle. The metabolism is boosted, blood circulation improves and all cells are supplied with sufficient oxygen and nutrients. Intense stress, such as that which occurs in competitive sports, can, however, promote oxidative stress. The reason - more energy has to be provided in the mitochondria. This means that more antioxidants can be used up than are available. Mental stress, caused by high levels of stress at work or in exam situations, can also lead to an increased need for antioxidants. Stress should therefore be avoided as far as possible or controlled with relaxation techniques.
What does an antioxidant diet look like?
Finally, a balanced diet is also important for cell protection. Since not all antioxidants are endogenous, i.e. are produced by the body itself, part of the requirement must be covered through food. Fresh fruit and vegetables are the best sources of antioxidants. This is because they contain not only the corresponding cell-protecting vitamins, but above all the valuable secondary plant substances, which are mainly found in peels and seeds. Teas, especially green tea, also have a high content of secondary plant substances. The German Nutrition Society advises against counteracting oxidative stress with individual substances. Anyone who still wants to support their body with nutritional supplements should use preparations whose complexity does justice to the metabolic processes and contains a mixture of vitamins, trace elements and secondary plant substances.
