Free radicals are unstable atoms that can damage cells, causing disease and aging. However, little is known about their role in human health or how to counteract their action.
They are “waste” molecules produced by normal cellular metabolism, which have the characteristic of being particularly “reactive” as they have a free electron, ready to interact with other molecules.
A certain level of ROS (ROS – Reactive Oxygen Species), the most studied free radicals, is fundamental in the general economy of the organism: it helps us, for example, to protect ourselves from the attacks of viruses and bacteria. However these molecules, if present in excess, can become dangerous precisely because of their oxidizing capacity, which leads them to attack other molecules of the body (DNA, proteins, lipids), damaging them.
It is the so-called oxidative stress, which represents a risk factor for health because it is able to accelerate the physiological cellular aging and favor a series of inflammatory or degenerative pathologies, such as hypertension, Alzheimer’s disease, diabetes, obesity, tumours.
We better understand how free radicals act, why they are harmful and how to defend ourselves from their action.
What are free radicals
They are molecules produced by normal cellular metabolism and therefore are essential for the survival of the organism, since almost all cells use them to produce energy through cellular respiration reactions. The waste products of these metabolic reactions also include free radicals, molecules that are very harmful to the cells themselves.
But what does free radical mean? Chemically, it consists of an atom or molecule that has at least one unpaired electron in its outermost orbital. This electron makes the free radical extremely unstable and reactive. In fact, it is capable of binding to other radicals or of subtracting an electron from other nearby molecules to “equalize” its electromagnetic charge.
Therefore, as soon as it is in the vicinity of a “target” molecule (ie with “available” electrons) the free radical “steals” the electron. The consequence, called “oxidant”, is that the free radical loses its potential danger. Instead, the molecule, deprived of an electron, in turn becomes a free radical, continuing the reaction previously triggered to the detriment of other molecules (glucides, lipids, amino acids, etc.).
This mechanism then creates new unstable molecules, triggering a “chain” reaction which, if not stopped in time, damages cellular structures.
To maintain balance, the body puts in place a defense system: antioxidants which supply free radicals with the electrons they lack. These are therefore substances capable of neutralizing the potentially harmful action of free radicals. Some of them are produced by our body. Others, however, such as vitamins C and E, must be introduced with food.
Classification of free radicals
The best known are ROS, (Reactive Oxygen Species), reactive oxygen species whose production is the natural consequence of normal cellular biochemical reactions, especially those that use oxygen to produce energy.
But there are also free radicals other than reactive oxygen molecules and just as harmful. Among these, the main ones are:
- RNS, or Reactive Nitrogen Species, in which the element that participates in the oxidizing action is nitrogen.
- RCS, or Reactive Carbon Species (with carbon content).
- RSS, or Reactive Sulfur Species (sulfur content).
How free radicals are formed
The production of free radicals represents an important and necessary physiological mechanism, because they play an important role in the communication between cells.
Furthermore, ROS come into play in the body’s defense system which uses them to fight pathogens such as bacteria and viruses and to stimulate immune functions.
Free radicals are a physiological product of cellular metabolism. Among the endogenous factors responsible for their production there are, for example:
- Aerobic energy production.
- The metabolism of fatty acids.
- The activity of cells in response to infection.
There is also a series of external factors that determine the production of free radicals. Between these:
- Air pollution.
- Taking drugs, alcohol, medications.
- Exposure to UV rays, radiation, chemicals or heavy metals, which can induce modifications in the DNA sequence with mutagenic effects on cells.
- Prolonged psycho-physical stress, also linked to intense physical activity: prolonged or too intense workouts, such as those of professional athletes, subject the body to high metabolic stress, resulting in an excessive production of free radicals that the body is unable to able to dispose. This reduces performance, causes post-workout soreness, impairs recovery and triggers generalized inflammation.
- Methods of cooking food: cooking on the grill, as well as all cooking at very high temperatures, determines the formation of benzopyrene, a highly harmful hydrocarbon for health.
Free radicals: what are they for?
Free radicals, as the result of normal cellular metabolism, are not harmful in themselves. On the contrary, they play an important role in the economy of the whole organism because they participate in various essential functions. But what functions do free radicals have?
Some of them are commonly used by our immune system, especially by a group of white blood cells known as polymorphonuclear leukocytes, which use them to be able to attack pathogenic bacterial cells and break them down. This is allowed by their very high reactivity, given by the presence of negatively charged oxygen atoms.
Disposal of waste cell materials
The same principle is the basis of another very important property of these molecules. In fact, they abound in a cellular organelle known as the peroxisome, which performs the function of “disintegrating wastebasket” inside our cell. Since free radicals are highly reactive molecules, these organelles have a modified outer membrane to not be attacked by these molecules.
At the same time, all the cellular waste materials are sent to these organelles, which if they accumulate inside the cell would risk preventing its regular functioning, leading to its death. In this way, all this material can be broken down into simpler molecules, which can be reused by the cell (as if it were the best of garbage recycling centers).
Programmed cell death
A final function of free radicals is linked to what is called “programmed cell death”, i.e. the process which causes, through the replication of some cells and the death of others, our body is able to differentiate one tissue from another other. In fact, how is it possible that all the tissues that characterize a human being differ from the same initial egg cell? This also happens thanks to the action of free radicals and their ability to regulate the life (and, above all, the death) of some cells instead of others, all under the “control” of our DNA.
In order for these molecules not to be harmful to our body, the delicate balance between their production and disposal must nevertheless be maintained.
Free radicals and antioxidants
Given that the production of free radicals is a physiological process that cannot be stopped, our body has developed a defense mechanism against these substances, made up of molecules capable of binding to ROS, inactivating them. These are antioxidants, partly produced by our cells (endogenous), partly taken with food (exogenous). This system ensures that the presence of free radicals in our body never exceeds the danger levels that can put our health at risk.
For this to happen, however, there must be a balance between free radicals and antioxidants. If this does not happen, the free radicals accumulate and become harmful, setting off a chain of oxidation reactions capable of altering the proteins, the phospholipids of cell membranes or the nucleic acids (DNA and RNA), with even very serious damage. In this case, we speak of oxidative stress.
Free radicals and oxidative stress
Oxidative stress can be defined as the disruption of the physiological balance between the production and elimination of free radicals. It is a pathological condition that can be localized, when the lesions caused by free radicals are limited to specific areas of the organism (for example the nervous system or the cardiovascular system) or systemic, if they involve it in its entirety.
But what are the causes of oxidative stress? This condition can be the result of:
- An increased production of free radicals.
- A less effective antioxidant defense of the body.
- Both of these factors.
Too many free radicals: what could it be due to?
The overproduction of ROS can be caused by physical, chemical or biological agents, such as exposure to radiation or pollutants, abuse of alcohol and drugs, viruses, bacteria, stress. At the origin of the surplus of free radicals there may also be endogenous causes and this occurs, in almost all cases, due to those processes that involve the movement of charges from a molecule…