Free radicals have a terrible reputation. These reactive and unstable molecules are associated with cancer, aging and degenerative diseases such as Alzheimer's disease.
However, the body constantly produces free radicals, which are a key part of life-sustaining processes such as respiration, cell signaling and defense against disease. So are free radicals really that bad, or do they have some underappreciated benefits?
And this is not just a one-time event, he said Michael Murphymitochondrial biologist at the University of Cambridge. “If a radical removes an electron, it leaves behind an unpaired electron, and it will react further. The result is often a nasty chain reaction.”
However, this problematic force can also be used by the body under controlled circumstances. immune system uses radicals to attack pathogens and protect against disease, while other one-electron compounds such as nitric oxide (NO) are used as signaling molecules for communication between different cells.
“Some enzymes use free radical chemistry within their active sites because it gives them the ability to perform more complex chemistry,” Murphy told Live Science. Consequently, many fundamental reactions of the body, from respiration to oxygen transport, depend on radical intermediates. chemistry possible.
In fact, the majority of radicals in the body—about 90%—are generated mitochondriathe cellular mechanism responsible for respiration said Michael Ristowlongevity researcher at the Charité Medical University in Berlin.
Respiration is a life-sustaining process that releases energy through the breakdown of glucose and oxygen. The entire process involves a complex sequence of steps mediated by a series of proteins called the electron transport chain. These proteins pass electrons between different units during this sequence of reactions, but little leakage means that some radicals are also released into the surrounding cellular environment.
“What can happen is that electrons are stripped from these enzymes and react with oxygen to form an oxygen free radical called superoxide—this is often a proximal free radical produced in biology,” Murphy explained. “Hydrogen peroxide (which is not a free radical) is then formed and this can be particularly harmful in the presence of ferrous iron (Fe2+). This creates another radical called a hydroxyl radical, which just reacts with anything.”
This is all part of the normal functioning of every cell, so free radicals only really become a problem when they are generated in large quantities, Ristow says.
“The body has evolved many different defense mechanisms,” he explained. A healthy diet naturally includes antioxidant molecules such as vitamins C and E that can quench these reactive species. “In addition, there are special enzymes that convert free radicals into less dangerous intermediates, and there is the glutathione system,” a sulfur-containing molecule that acts as a sacrificial sponge, mopping up free radicals before they are processed by another enzyme.
However, certain environmental factors, such as UV exposure or excessive alcohol consumption, can trigger the production of higher levels of free radicals through a slightly different mechanism. “UV radiation can react with so-called photosensitizers. The molecule goes into an excited state, absorbing energy, and then often transfers that energy to oxygen,” Murphy explained. “The chemistry is a little complicated, but you convert oxygen into a more reactive form of oxygen, which then acts on fat and other double bonds.”
After a certain point (which is different for everyone), these additional radicals overload the body's natural defense mechanisms. The result: tissue damage, which over time leads to diseases such as cancer.
But crucially, there is growing evidence that controlled levels of free radicals are actually beneficial or even necessary for health – part of a phenomenon known as hormesis.
“The response to free radical exposure at the systemic level is typically to increase free radical responsiveness,” Ristow said. “In this way, the entire human body becomes better equipped to deal not only with free radicals, but also with toxic food components, ultraviolet radiation and other sources of damage.”
This effect is most pronounced in the context of exercise.
“If you take antioxidants before or along with exercise, the effect of exercise on health parameters disappears or is significantly reduced,” Ristow said. Endurance, recovery, muscle mass gain And insulin resistance are affected, and although there are several theories about the role of radicals in each case, there is currently no consensus in this area.
Free radicals can clearly cause harm, but the question of whether they are good or bad has a much more nuanced answer that depends on both context and concentration. “It’s a balance,” Ristow said. “But if ROS were really only harmful, then evolution would eliminate them!”
This article is for informational purposes only and is not intended to provide medical or dietary advice.
