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# Free Radicals

free rad·i·cals - free RAD-ih-kulz

## Definition

Free radicals are unstable, highly reactive molecules that have one or more unpaired electrons in their outer shell. This unpaired electron makes the molecule chemically aggressive - it 'steals' electrons from nearby molecules (proteins, fats, DNA) to stabilize itself, damaging those molecules in the process. The damaged molecule then becomes a free radical itself, triggering a chain reaction of molecular damage called [oxidative stress](/glossary/oxidative-stress).

Free radicals are produced naturally as byproducts of normal metabolic processes, particularly during energy production in the [mitochondria](/glossary/mitochondria). Your immune system also deliberately generates free radicals to kill bacteria and viruses. In moderate amounts, free radicals serve important signaling and defense functions. The problem arises when free radical production exceeds the body's capacity to neutralize them with antioxidants - creating an imbalance known as oxidative stress.

External sources that increase free radical exposure include air pollution, cigarette smoke, UV radiation, pesticides, industrial chemicals, excessive alcohol, processed foods, and even intense exercise without adequate recovery. Over time, accumulated free radical damage to cells, proteins, and DNA is thought to contribute to aging, cancer, [cardiovascular](/glossary/cardiovascular) disease, neurodegenerative diseases, and many other chronic conditions. This is why antioxidant-rich diets and healthy lifestyle practices are emphasized in preventive health.

## Also Known As

Reactive oxygen species (ROS) Oxidants 

## Key Facts

-   • The most common free radicals in the body are reactive oxygen species (ROS) including superoxide, hydroxyl radical, and hydrogen peroxide. 
-   • Your body produces antioxidant enzymes (superoxide dismutase, catalase, glutathione peroxidase) as its primary defense against free radicals. 
-   • Dietary antioxidants including vitamins C and E, beta-carotene, selenium, and polyphenols help neutralize free radicals. 
-   • The 'free radical theory of aging' proposes that accumulated oxidative damage is a primary driver of the aging process. 
-   • Moderate exercise initially increases free radical production but stimulates the body to build stronger antioxidant defenses over time. 

## How It Relates To Your Health

Understanding free radicals helps explain why antioxidant-rich diets (abundant in colorful fruits and vegetables, nuts, seeds, and whole grains) are consistently associated with reduced risk of chronic diseases. However, high-dose antioxidant supplements have not shown the same benefits and may even be harmful in some populations - the body's own antioxidant defense system works best when supported by dietary antioxidants in their natural context.

Free radical damage is measured clinically through biomarkers of oxidative stress such as malondialdehyde (MDA), 8-hydroxydeoxyguanosine (8-OHdG), and F2-isoprostanes. These markers are used in research settings and increasingly in [functional medicine](/glossary/functional-medicine) to assess oxidative burden.

## Related Terms

[Oxidative Stress](/glossary/oxidative-stress)[Anti-inflammatory](/glossary/anti-inflammatory)[Phytonutrients](/glossary/phytonutrients)[Mitochondria](/glossary/mitochondria)[Detoxification](/glossary/detoxification)

## Related Articles

[![The Mediterranean Diet: A Complete Beginner's Guide](https://images.unsplash.com/photo-1498837167922-ddd27525d352?w=1200&h=630&fit=crop&fm=webp)](/nutrition/mediterranean-diet-beginners-guide)

[](/nutrition/mediterranean-diet-beginners-guide)[Nutrition & Diet](/nutrition)

### The Mediterranean Diet: A Complete Beginner's Guide

2026-01-20

## Sources

1.  [Free Radicals, Antioxidants and Functional Foods](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3249911/) - National Library of Medicine
2.  [Antioxidants: In Depth](https://www.nccih.nih.gov/health/antioxidants-in-depth) - National Center for Complementary and Integrative Health (NIH)
3.  [Free Radicals and Oxidative Stress](https://www.health.harvard.edu/staying-healthy/understanding-antioxidants) - Harvard Health Publishing

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