The Antioxidant Effect in the Body – Free Radicals and Natural Antioxidants

Unpaired-electron species, commonly referred to as free radicals, constitute atoms or molecular entities distinguished by the presence of at least one unpaired electron within their valence shell. Their formation arises from the homolytic cleavage of covalent bonds, wherein each of the two resulting molecular fragments retains one of the originally shared electrons. The resultant system exhibits profound thermodynamic instability, imparting upon these radicals an exceptionally high chemical reactivity—continuously seeking either to acquire an additional electron from surrounding molecules or to donate their surplus electron. Radical-mediated processes manifest as chain reactions, comprising three distinct phases: **initiation** (the generation of primary radical species), **propagation** (the cascading amplification of radical reactions), and **termination** (the recombination of two radicals into a stable, non-radical compound). While this mechanism may appear abstract and detached from human biology, free radicals are in fact ubiquitous in metabolic pathways, particularly those occurring under oxygen-rich conditions. Their endogenous sources include oxidative reactions associated with cellular respiration, where reactive oxygen species (ROS) are generated. Within the human body, the primary targets of radical-induced damage are macromolecular structures: structural and enzymatic proteins, nucleic acids (DNA/RNA), polyunsaturated fatty acids (PUFAs), membrane polysaccharides, and lipids—including cholesterol. Of particular concern is lipid peroxidation, a self-perpetuating oxidative process yielding toxic lipid peroxides. These, in turn, trigger a cascade of deleterious effects: in the skin, they degrade collagen and elastin fibers, accelerating aging (wrinkle formation, loss of elasticity); in the cardiovascular system, they damage endothelial linings and promote atherosclerotic plaque formation via lipoprotein oxidation; and in genetic material, they induce proto-oncogenic mutations, elevating cancer risk. Exogenous sources of free radicals include UV radiation (photolysis of atmospheric molecules), combustion of fossil fuels, tobacco smoke (a single puff releases approximately 10¹⁴ radical particles), air pollution (ozone, nitrogen oxides), heavily processed foods rich in oxidized fats (fried products, cured meats), and certain pharmaceuticals metabolized by cytochrome P450 enzymes. Endogenous factors exacerbating radical production include chronic oxidative stress (excessive ROS generation coupled with antioxidant deficiency), inflammatory states, viral/bacterial infections, and metabolic disorders (diabetes, obesity). Physiologically, moderate levels of free radicals serve regulatory roles—participating in cellular signaling, pathogen clearance (phagocytosis), and xenobiotic detoxification. However, their overproduction disrupts redox homeostasis, culminating in **oxidative stress**—a pathological condition that accelerates aging, tissue degeneration, and the onset of civilization diseases such as atherosclerosis, malignancies, neurodegenerative disorders (Alzheimer’s, Parkinson’s), and type 2 diabetes.

Antioxidants, alternatively referred to as redox-protective compounds, constitute a diverse class of biologically active chemical entities whose primary role involves the inhibition or substantial deceleration of oxidative degradation in organic molecules, alongside the neutralization of reactive oxygen and nitrogen species—commonly termed free radicals. Scholarly classifications distinguish between two core subgroups: endogenous antioxidants (synthesized in situ by cellular machinery as part of normal metabolic functions, such as glutathione, coenzyme Q10, or enzymatic systems like superoxide dismutase) and exogenous antioxidants (acquired externally via dietary intake, predominantly from polyphenol-rich foods, vitamins C and E, carotenoids, and flavonoids).

In a healthy, youthful individual, antioxidant defense systems typically operate with high efficiency, maintaining a delicate balance between the generation and detoxification of free radicals. However, with advancing age, the efficacy of these protective mechanisms gradually declines. When compounded by environmental stressors—including chronic oxidative stress induced by tobacco smoking, exposure to atmospheric pollutants, micronutrient-deficient diets, or excessive ultraviolet radiation—this decline leads to the cumulative accumulation of oxidative cellular damage. Consequently, it becomes imperative to consciously augment one’s diet with foods demonstrating robust antioxidant capacity (e.g., berry fruits, cruciferous vegetables, nuts, and green tea) to ensure adequate systemic levels of these compounds and mitigate the risk of redox imbalance favoring pro-oxidative states.

It is critical to emphasize that—much like the detrimental effects of excess free radicals—excessive antioxidant supplementation may also yield adverse outcomes. Supraphysiological concentrations of antioxidants within tissues can disrupt the physiological signaling roles of reactive oxygen species, which, in moderation, serve as essential mediators in cellular processes such as apoptosis, angiogenesis, and immune responses. Furthermore, the accelerated neutralization of inflammatory states—while beneficial in chronic disease contexts—may impede the short-term, controlled inflammatory responses necessary for initiating tissue repair mechanisms. Thus, maintaining redox homeostasis is advised, avoiding both deficiency and surplus of antioxidant compounds to preserve optimal cellular function.

The disruption of equilibrium between the generation of reactive oxygen species and the organism’s capacity to efficiently eliminate their excess or repair the cellular damage they induce is defined as oxidative stress. In response to this phenomenon, the human biological system has evolved a sophisticated antioxidative defense mechanism that includes the synthesis of specialized enzymes—among which superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT) are particularly notable. These enzymes play a pivotal role in the continuous surveillance and eradication of oxygen-free radicals circulating within tissues. Meanwhile, exogenous and dietary antioxidants exhibit the ability to directly bind with reactive molecules by donating the deficient electron, thereby stabilizing the radical’s structure. This process, involving the transfer of an unpaired electron from the antioxidant molecule to the free radical, results in the neutralization of the latter. The neutralized radicals are subsequently metabolized and excreted from the body, while certain antioxidants may undergo regeneration and participate in subsequent defense cycles.

While the human body possesses an innate, multilayered defense mechanism designed to neutralize reactive oxygen species, the physiological aging process is invariably accompanied by a gradual decline in the efficiency of endogenous antioxidant synthesis. Consequently, the systematic intake of exogenous antioxidants through a well-balanced diet emerges as an indispensable compensatory strategy. Upon entering the gastrointestinal tract via food consumption, these bioactive compounds undergo intricate interactions with gastric hydrochloric acid, digestive enzymes, bile acids and their conjugate salts, as well as the diverse intestinal microbiota and their metabolic byproducts. Collectively, these factors trigger a cascade of biotransformation reactions that both activate and structurally modify antioxidant molecules, thereby enabling their effective neutralization of reactive oxygen species before these can convert into highly destructive free oxygen radicals. The most significant dietary antioxidants include polyphenolic compounds (such as flavonoids and anthocyanins), coenzyme Q10, vitamins with established antioxidant properties (notably ascorbic acid, tocopherols, retinol, and its provitamin beta-carotene), and trace elements of critical importance (particularly selenium). The richest sources of these compounds are fresh fruits and vegetables—including their processed derivatives—whole-grain cereal products, legumes, tea infusions, coffee, fermented alcoholic beverages (wine and beer), and aromatic herbs and spices. Particular emphasis is placed on berry fruits, which are abundant in anthocyanins, and citrus fruits, which represent an exceptionally valuable source of citrus flavonoids with well-documented antioxidant potential. Among vegetables, garlic (rich in allicin), leafy cruciferous varieties (such as kale, Brussels sprouts, and broccoli), spinach, beets, and tomatoes (containing lycopene) are especially noteworthy. The daily consumption of at least five servings of fruits and vegetables ensures optimal provision of exogenous antioxidants, constituting a fundamental component in the prevention of oxidative stress—the primary pathomechanism underlying accelerated cellular aging and the development of inflammation-driven chronic diseases. It is crucial to emphasize that the body’s oxidative-reductive homeostasis relies on a delicate balance between pro-oxidants and antioxidant systems, whose relative proportions must remain in dynamic equilibrium. Even with a fully functional endogenous antioxidant defense, dietary supplementation rich in natural antioxidant compounds remains an invaluable support for maintaining this balance, particularly in the context of contemporary environmental factors that exacerbate oxidative stress.