What Are Antioxidants?

Reviewed by SOMA HEALTH's Medical Research Team

Antioxidants are one of the most talked-about ideas in nutrition and one of the most misunderstood. At their core they are simply molecules that help keep reactive chemistry inside your cells under control. Understanding what they actually do makes it easier to see where food, your own biology, and compounds like the postbiotic urolithin A each fit.

The chemistry behind the word

Every cell in your body runs on chemical reactions, and many of those reactions involve electrons moving from one molecule to another. Occasionally a molecule ends up with an unpaired electron. These molecules are called free radicals, and a large family of them that contain oxygen are known as reactive oxygen species (ROS). Because an unpaired electron is unstable, a free radical tends to grab an electron from whatever is nearby, which can turn that neighbor into a new radical and start a small chain reaction.

An antioxidant is any molecule that can safely donate an electron to a free radical without becoming dangerously reactive itself. By satisfying the radical's need for an electron, the antioxidant stops the chain reaction before it can damage proteins, cell membranes, or DNA. That is the entire concept in a sentence: antioxidants are electron donors that help neutralize unstable, electron-hungry molecules.

It is worth being precise, because marketing often is not. Free radicals are not villains to be eliminated. Your body produces them on purpose. They act as signaling molecules, help immune cells destroy bacteria, and are a normal by-product of turning food and oxygen into energy. The goal is not zero free radicals; it is balance. Scientists call the tilt toward too many reactive molecules, relative to your defenses, oxidative stress.

Your body makes its own antioxidants

People tend to think of antioxidants as something you eat, but your most important antioxidant defenses are ones your body manufactures itself. These endogenous systems are enzymes and small molecules that work continuously, everywhere, at high speed.

The enzyme front line

Three enzyme systems do most of the heavy lifting. Superoxide dismutase (SOD) converts a common radical called superoxide into hydrogen peroxide. Catalase and the glutathione peroxidase enzymes then break that hydrogen peroxide down into water. Glutathione itself, a small molecule your cells make from amino acids, is often described as the master antioxidant because it is present in large amounts and can be recycled and reused many times.

What matters here is that these systems are catalytic and regenerating. A single enzyme molecule can neutralize reactive molecules over and over. This is very different from a dietary antioxidant, which is generally used up once it donates its electron. It is one reason why the health of your internal machinery often matters more than any single food.

Dietary antioxidants: helpful, but often oversold

Diet contributes a second layer of antioxidant support. Vitamin C is water soluble and works in the watery interior of cells and in blood. Vitamin E is fat soluble and protects cell membranes. Carotenoids such as beta-carotene and lutein, along with the enormous family of plant polyphenols found in berries, tea, coffee, cocoa, and colorful vegetables, add further capacity.

Here honesty matters. For decades the assumption was that swallowing large doses of isolated antioxidants would slow aging and prevent disease. Large human trials of high-dose antioxidant supplements have been, on the whole, disappointing, and a few even showed harm at high doses. The likely explanation is that antioxidant biology is a finely tuned network, not a bucket you simply fill. Whole foods deliver these compounds in modest, balanced amounts alongside fiber and other nutrients, which is part of why a diet rich in plants consistently looks better than isolated megadoses. None of this is a claim that any antioxidant treats or prevents disease; it is a description of what the research does and does not support.

Where urolithin A fits, and where it does not

Urolithin A is frequently mentioned alongside antioxidants, so it is worth placing it accurately. Urolithin A is a postbiotic: a compound your gut bacteria produce when they break down ellagitannins, the parent compounds found in pomegranates, walnuts, and certain berries. Not everyone's microbiome makes it efficiently, which is part of why interest in taking it directly has grown.

The important distinction is mechanism. Urolithin A is not primarily studied as a free-radical scavenger in the way vitamin C is. Its most-studied action is support for mitophagy, the housekeeping process by which cells identify worn-out mitochondria and recycle them so that fresher, better-functioning ones can take their place. Because damaged mitochondria tend to leak more reactive oxygen species, keeping the mitochondrial population in good repair is a different and more upstream way of influencing cellular oxidative balance than mopping up individual radicals after the fact.

What does the human evidence show? In humans, the first-in-human trial by Andreux and colleagues (Nature Metabolism, 2019) reported that urolithin A was safe and well tolerated at doses up to 1,000 mg per day and shifted mitochondrial gene-expression signatures. Later randomized trials in older adults (Liu and D'Amico, JAMA Network Open, 2022) and in middle-aged adults (Singh, Cell Reports Medicine, 2022, testing 500 and 1,000 mg) reported effects on muscle endurance, strength, and exercise performance. A 2025 randomized trial in Nature Aging reported support for immune-cell mitochondrial health in midlife adults. These are structure and function findings about muscle and mitochondrial biology, not antioxidant disease claims. Much of the deeper cellular work, including the original demonstration of enhanced mitophagy, comes from preclinical research in worms and rodents (Ryu, Nature Medicine, 2016) and should be read as such. A 2024 systematic review in Ageing Research Reviews describes the human evidence for aging-related benefits as still emerging.

Antioxidants versus mitochondrial support: two different strategies

It helps to hold both ideas at once. Classic antioxidants act like a fire brigade, neutralizing reactive molecules as they appear. Mitochondrial quality control acts more like building maintenance, keeping the equipment that both produces energy and generates most of your everyday reactive oxygen species in good working order. Neither replaces the other, and neither is a shortcut around the basics.

Those basics are unglamorous but real. A plant-forward diet supplies a broad mix of dietary antioxidants. Regular exercise, perhaps counterintuitively, is one of the most reliable ways to strengthen your own endogenous antioxidant enzymes, because the mild oxidative signal of a workout prompts your cells to build more defenses. Adequate sleep, not smoking, and moderate sun exposure round out the list. Supplements, urolithin A included, sit on top of that foundation rather than substituting for it.

If you want to go deeper on the mechanism that makes urolithin A distinct from ordinary antioxidants, our guide to mitophagy walks through the recycling process step by step, and our overview of mitochondrial health explains why these tiny structures sit at the center of energy and aging. For the full picture on the compound itself, start with the complete urolithin A guide, and if you are weighing products, our roundup of the best urolithin A gummies compares formats and doses.

A brief, important note: the topics above touch on energy, aging, and general wellbeing, but nothing here is a treatment for any medical condition. If you have symptoms such as persistent fatigue or a diagnosed health issue, that is a conversation for your doctor, not a supplement label.

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This guide is educational and is not a substitute for advice from a qualified healthcare provider.