Abstract Antioxidants are important compounds that contribute to protecting human cells from damage caused by free radicals and oxidative stress. These compounds are naturally present in the human body and can also be obtained from various dietary sources, such as fruits, vegetables, and nuts. An imbalance in oxidative status may be associated with an increased risk of certain chronic diseases, including cardiovascular diseases, diabetes, and neurological disorders. This article aims to explain the concept of antioxidants, their types and sources, and their role in maintaining human health. It also highlights their importance in health prevention and future medical applications. The article emphasizes the importance of balanced nutrition and a healthy lifestyle in supporting the body's natural defense systems. Keywords: Antioxidants, Oxidative Stress, Free Radicals, Public Health, Nutrition, Cellular Protection. Introduction Maintaining biological balance within the human body is essential for ensuring the normal functioning of cells and tissues. During various metabolic processes, the body produces reactive molecules known as free radicals, which can affect cellular components when their levels increase. Antioxidants play an important role in reducing the effects of these molecules and maintaining cellular integrity. The importance of studying these compounds has increased because oxidative stress is associated with several chronic diseases, making them an important topic in biochemical and medical research. Concept and Types of Antioxidants Antioxidants are a group of compounds that help reduce harmful oxidation reactions by neutralizing free radicals or limiting their effects on cellular components. Antioxidants are mainly classified into two major types: enzymatic and non-enzymatic antioxidants. Enzymatic antioxidants include superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx). Non-enzymatic antioxidants include vitamin C, vitamin E, glutathione, and several plant-derived compounds such as flavonoids and polyphenols. These compounds differ in their chemical structures and mechanisms of action, but they share a protective role against oxidative damage. Role of Antioxidants in Cellular Protection Antioxidants play an important role in protecting cells against damage caused by the accumulation of free radicals. These reactive molecules can interact with cellular components, including proteins, lipids, and nucleic acids, potentially leading to changes in their normal functions. Antioxidants help reduce lipid oxidation and protect cellular membranes. They also contribute to maintaining the integrity of proteins and genetic material (DNA). These protective functions are essential for the normal continuation of biological processes. Oxidative Stress and Its Relationship with Diseases Oxidative stress occurs when the production of free radicals increases beyond the capacity of antioxidant defense systems to control them. This imbalance may be associated with several medical conditions, including cardiovascular diseases, diabetes, and certain neurological disorders. Scientific studies have also indicated a relationship between oxidative stress and some processes involved in cancer development, due to the possibility of DNA damage and alterations in the regulation of cell growth. Dietary Sources of Antioxidants Natural foods are among the most important sources of antioxidants required by the body to maintain normal biological functions. Fruits and vegetables contain various antioxidant compounds, including vitamin C, carotenoids, and polyphenols. Important dietary sources include citrus fruits, berries, pomegranates, tomatoes, carrots, spinach, nuts, and green tea. Consuming a balanced and varied diet helps provide different nutritional compounds that support the body's natural defense systems. Effects of Lifestyle on Oxidative Stress Oxidative stress levels are influenced by several environmental and lifestyle factors, such as smoking, exposure to air pollution, poor nutrition, and physical inactivity. These factors may contribute to increased free radical production and affect the efficiency of the body's natural defense systems. Therefore, adopting a healthy lifestyle that includes regular physical activity, consuming antioxidant-rich foods, and avoiding smoking can help support oxidative balance and maintain overall health. Conclusion Antioxidants represent an important component of the human body's natural defense systems because of their role in reducing oxidative damage and maintaining the integrity of cells and tissues. Understanding their mechanisms of action and dietary sources helps increase awareness of their health benefits. Further scientific research is needed to develop new compounds and evaluate their biological activities, contributing to future medical and research applications and improving quality of life. Al-Mustaqbal University – The First University in Iraq