antioxidants

Antioxidants are a broad and diverse group of compounds found in foods and produced by the body that help prevent or slow the oxidative damage that occurs when free radicals interact with molecules such as DNA, proteins, and lipids. Free radicals are unstable atoms or molecules produced by normal metabolic processes (like cellular respiration) and by external exposures (such as pollution, ultraviolet light, and cigarette smoke). Over time, accumulation of oxidative damage from free radicals—often referred to as oxidative stress—has been associated with aging and the development of chronic diseases, including cardiovascular disease, certain types of cancer, and neurodegenerative conditions. Unlike essential vitamins and minerals that have established recommended daily allowances, antioxidants as a collective group do not have an official daily intake value because they encompass thousands of individual compounds with distinct chemical structures and physiological properties. Chemically, antioxidants are capable of donating an electron to a free radical without becoming unstable themselves, thereby neutralizing the free radical and halting chain reactions that can damage cells. Common antioxidant nutrients include vitamins C and E, carotenoids (such as beta‑carotene, lutein, and lycopene), selenium (a trace mineral that is a cofactor for antioxidant enzymes), and a vast array of plant‑derived phytonutrients, including polyphenols, flavonoids, anthocyanins, and phenolic acids. Many antioxidant molecules are colorful plant pigments; for example, the deep blue of blueberries comes from anthocyanins, while the red of tomatoes reflects lycopene content. Antioxidants play roles not only in neutralizing free radicals but also in modulating cellular signaling pathways, influencing gene expression related to inflammation and cell survival, and supporting the immune system. While the body produces some antioxidant enzymes endogenously (such as superoxide dismutase and glutathione peroxidase), the majority of antioxidant compounds come from the diet, especially from fruits, vegetables, whole grains, nuts, seeds, herbs, and spices. The concept of antioxidants has become widespread in nutrition and health communications, often highlighting their potential to contribute to longevity and disease prevention. However, it is important to recognize that antioxidants function within complex biochemical networks, and their activity in the human body depends on absorption, metabolism, and interaction with other nutrients and signaling systems.

Antioxidants help protect the body's cells from damage caused by oxidative stress, a state that arises when free radicals exceed the body’s natural antioxidant defenses. Through donation of electrons to free radicals, antioxidants mitigate the chain reactions that lead to cellular injury. This fundamental mechanism underpins a wide range of proposed health benefits associated with diets high in antioxidant‑rich foods. Oxidative stress has been implicated in the pathogenesis of chronic illnesses, including atherosclerosis, neurodegeneration, cancer, and diabetes; antioxidants may play a role in slowing the progression of these conditions by reducing oxidative damage. For example, carotenoids like beta‑carotene and lycopene can protect lipid membranes and DNA from oxidative harm, while flavonoids and polyphenols influence inflammatory signaling cascades. Epidemiological studies consistently show that higher intake of fruits and vegetables—rich sources of antioxidant nutrients—is associated with lower risks of cardiovascular disease. This association may reflect antioxidant activity as well as other beneficial effects such as improved endothelial function and reduced inflammation. Some research suggests that specific antioxidant compounds can support vascular health by enhancing nitric oxide availability, improving blood flow regulation, and reducing low‑density lipoprotein oxidation—a key step in the development of atherosclerosis. Similarly, antioxidants like lutein and zeaxanthin accumulate in the retina and may help protect eye tissues from light‑induced oxidative damage, potentially reducing the risk of age‑related macular degeneration. The immune system also benefits from antioxidant support. Vitamin C, one of the most studied antioxidants, contributes to the function of various immune cells and has roles in inflammation regulation. Selenium is essential for the activity of glutathione peroxidase, an enzyme that helps neutralize peroxides and protect immune cells from oxidative damage. Polyphenols, such as those found in tea and cocoa, have been observed to influence immune cell signaling and may contribute to anti‑inflammatory effects. While antioxidant supplementation has been extensively studied, with trials focusing on vitamins C and E, beta‑carotene, and other compounds, results have been mixed and often fail to show significant benefits for disease prevention when supplements are used in isolation. Nonetheless, a diet naturally high in antioxidant‑rich foods remains a cornerstone of dietary recommendations aimed at promoting long‑term health and reducing the risk of chronic diseases.

Because ‘‘antioxidants’’ encompass a multitude of individual compounds with distinct biochemical identities, regulatory bodies such as the National Institutes of Health (NIH) have not established a recommended daily allowance (RDA) for antioxidants as a singular nutrient. Instead, many antioxidant compounds fall into categories of vitamins and phytonutrients with their own dietary recommendations or intake guidelines. For example, vitamin C, a well‑known antioxidant, has an RDA of 90 mg per day for adult males and 75 mg per day for adult females, while vitamin E has an RDA of 15 mg (22.4 IU) of alpha‑tocopherol for adults. Selenium, which supports antioxidant enzyme systems, has an RDA of 55 mcg per day for adults. These individual values illustrate how specific antioxidant nutrients are quantified, even though the broader category of ‘‘antioxidants’’ does not have a unified intake target. In practice, nutrition professionals emphasize achieving a wide variety of antioxidant compounds through diverse food choices rather than focusing on a single ‘‘antioxidant number.’’ Dietary patterns rich in fruits, vegetables, whole grains, nuts, seeds, and legumes naturally provide multiple antioxidants that work synergistically. The U.S. Dietary Guidelines and expert panels recommend at least five servings of fruits and vegetables per day, which by virtue of their phytochemical content, deliver a spectrum of antioxidant compounds. Instead of measuring total antioxidant ‘‘units,’’ healthcare professionals look at dietary patterns and biomarkers such as plasma levels of specific vitamins (for example, plasma vitamin C) or biomarkers of oxidative stress. Certain life stages and conditions may influence antioxidant needs. During periods of increased oxidative stress—such as chronic inflammation, exposure to pollutants, intense physical activity, or illness—dietary intake of antioxidant‑rich foods may be particularly beneficial. Pregnant and lactating individuals also benefit from adequate intake of specific antioxidant vitamins within established guidelines to support fetal development and maternal health. Older adults may face increased oxidative stress related to aging and chronic conditions; hence a nutrient‑dense diet with ample antioxidant sources is often recommended. Ultimately, the ‘‘need’’ for antioxidants is embedded within overall dietary quality, and consuming a colorful, plant‑forward diet is the most reliable strategy to ensure sufficient antioxidant exposure.

Unlike essential vitamins and minerals, antioxidants as a broad category do not have a defined deficiency syndrome because they encompass many compounds with varied roles and sources. Instead, deficiency states are recognized for specific antioxidant nutrients with established dietary requirements. For example, vitamin C deficiency leads to scurvy, characterized by fatigue, gum bleeding, and impaired wound healing. Vitamin E deficiency, which is rare, can result in neurologic problems due to poor nerve conduction. Selenium deficiency—uncommon in developed countries—can impair antioxidant enzyme systems and is associated with conditions such as cardiomyopathy in regions with low selenium soil content. Since ‘‘antioxidants’’ include both essential and non‑essential compounds, ‘‘deficiency’’ in antioxidants broadly is more a concept of inadequate intake of antioxidant‑rich foods rather than a clinical disease. Insufficient consumption of fruits and vegetables, whole grains, nuts, and seeds may lead to lower plasma levels of vitamin C, alpha‑tocopherol, carotenoids, and other antioxidant nutrients. Suboptimal levels of these compounds could theoretically increase susceptibility to oxidative stress, although direct causal links to specific health outcomes are complex and influenced by many factors. Low vitamin C status can be assessed via plasma concentration measurements, with values below 11 µmol/L generally indicating deficiency; suboptimal levels are often considered below 28 µmol/L. Vitamin E status is typically assessed by serum alpha‑tocopherol concentration, with insufficiency suggested when levels are below the reference range established by clinical laboratories. Selenium status can be evaluated using plasma or serum selenium, although optimal ranges vary by assay and population. At‑risk populations for inadequate intake of antioxidant nutrients include individuals with limited access to fresh produce, those following restrictive diets without adequate variety, older adults with diminished appetite or nutrient absorption, and people with chronic illnesses that increase oxidative stress or nutrient depletion. Smokers have increased oxidative burden and may require higher intake of antioxidant‑rich foods. However, ‘‘deficiency’’ in the broad sense remains a dietary concept rather than a defined clinical condition, and addressing low intake involves improving overall diet quality rather than treating a discrete disease state.

Common Forms: Vitamin C, Vitamin E (alpha‑tocopherol), Carotenoid complexes, Polyphenol extracts

Typical Doses: Follow individual nutrient recommendations (e.g., vitamin C 75–90 mg/day).

When to Take: With meals to enhance absorption.

Best Form: Dependent on specific compound (e.g., natural vitamin E d‑alpha‑tocopherol)

⚠️ Interactions: High vitamin E may interact with blood thinners.