The Discovery of Free Radicals

The concept of free radicals—unstable molecules that can damage cells—began in the early 20th century in chemistry. Free radicals are molecules or atoms with an unpaired electron, which makes them highly reactive. In the 1950s, the American scientist Denham Harmon connected this chemical idea to human health.

In 1954, Harmon published an influential paper in the Journal of Gerontology introducing what became known as the Free Radical Theory of Aging. He argued that free radicals, generated during normal metabolism and from outside exposures (like radiation or pollution), could cause cumulative damage to cells, leading to aging and disease. This was groundbreaking because it suggested that something as small and invisible as a molecule could influence how long we live and how healthy we are.

Harmon continued refining his theory through the 1970s and 1980s, proposing links between free radicals, cancer, and heart disease. Though widely cited, his ideas were initially met with skepticism. Surprisingly, Harmon did not receive a Nobel Prize for this work, even though his theory profoundly influenced modern biology and nutrition.

Sidebar Timeline: Antioxidants and Free Radicals

• 1922 – Vitamin E discovered by Herbert Evans & Katharine Bishop.
• 1930s – Vitamin C isolated and identified as the anti-scurvy nutrient.
• 1954 – Denham Harmon publishes Free Radical Theory of Aging.
• 1969 – Irwin Fridovich & Joe McCord discover the enzyme superoxide dismutase (SOD).
• 1970 – Linus Pauling publishes Vitamin C and the Common Cold.
• 1980s – Helmut Sies popularizes the term “oxidative stress.”
• 1990s – Antioxidants become a central theme in supplement and natural food marketing.

Other Key Scientists

While Harmon laid the foundation, several others expanded the field:

• Irwin Fridovich and Joe McCord (1969) discovered the enzyme superoxide dismutase (SOD), proving the body has built-in antioxidant defenses.
• Bruce Ames (1970s–1990s) showed that fruits and vegetables protect DNA partly through antioxidants.
• Helmut Sies (1980s) introduced the concept of oxidative stress, now a central medical term.
• Linus Pauling (1970s) helped bring antioxidants, especially vitamin C, into public awareness.

Together, these researchers established free radicals and antioxidants as a mainstream field of study.

Antioxidants: Nature’s Defense System

Free radicals may sound destructive, but the body has its own defenses. Antioxidants are compounds that can safely neutralize free radicals by donating an electron without becoming unstable themselves.

Two major antioxidant vitamins became especially well-known:

• Vitamin E – a fat-soluble antioxidant, meaning it works in fatty parts of the body such as cell membranes, protecting lipids (fats) from oxidation.
• Vitamin C – a water-soluble antioxidant that works in blood plasma and other watery environments. Already famous for preventing scurvy, vitamin C gained renewed attention in the 1970s when Linus Pauling promoted it as a protector against colds and chronic disease. Importantly, vitamin C can also regenerate oxidized vitamin E back into its active form.

Beyond vitamins, researchers identified several classes of plant-based antioxidants, including:

• Polyphenols (in fruits, tea, coffee, wine, cocoa)
• Carotenoids (beta-carotene, lycopene, lutein, etc.)
• Flavonoids (in berries, citrus, soy, onions, and green tea)

These discoveries helped explain why diets rich in fruits and vegetables consistently show strong links with lower risks of cancer, heart disease, and other chronic illnesses.

Analogies for Free Radical Damage

To make the idea of oxidation clearer, it helps to compare it to everyday life:

• Rusting metal: Rust forms when oxygen in the air reacts with iron atoms, stealing their electrons in a chemical process called oxidation. Free radicals are unstable oxygen-containing species that accelerate this reaction. In the body, something similar happens: oxygen-derived free radicals “oxidize” fats, proteins, and DNA, slowly wearing down tissues.
• Cracking rubber: Rubber (like a windshield wiper blade) becomes brittle and cracks after long exposure to oxygen and sunlight. That brittleness is due to oxidation reactions breaking down the rubber’s structure. Our own tissues, constantly bathed in oxygen, undergo similar stress.

These analogies are scientifically appropriate and illustrate why living in an oxygen-rich atmosphere requires us to have protection. Oxygen is essential for life, but it also creates the potential for oxidative damage. That’s why organisms, including humans, evolved antioxidant defenses—both from the foods we eat and from enzymes our bodies make.

Without antioxidants, oxygen would eventually “burn up” our cells much the way it rusts iron or cracks rubber.

From Science to the Natural Foods Movement

While Harmon’s papers in the 1950s set the stage, the integration of antioxidants into popular nutrition and the natural health movement came later:

• 1960s–1970s: Health food pioneers began embracing the idea that diet could prevent disease. Vitamin E and C supplements were available, but their antioxidant roles became more widely emphasized as Harmon’s theory spread.
• 1970s: Linus Pauling’s Vitamin C and the Common Cold (1970) brought antioxidants into the public spotlight.
• 1980s–1990s: Research highlighted fruits and vegetables as sources of plant-based antioxidants. The term “antioxidant” began appearing on supplement and natural food labels.
• 1990s–2000s: Large-scale studies tested antioxidant vitamins for preventing heart disease and cancer. Results were mixed, but antioxidants remained central to both mainstream nutrition and natural health culture.

Conclusion

The story of antioxidants shows how an abstract chemical idea became part of everyday nutrition. Denham Harmon first connected free radicals to aging in 1954. Irwin Fridovich, Joe McCord, Bruce Ames, Helmut Sies, and Linus Pauling further developed and popularized the science.

Although Harmon never won a Nobel Prize, his theory reshaped biology and nutrition. Today, antioxidants are not only the subject of serious biomedical research but also a foundation of the natural food and supplement movement, symbolizing the belief that the right diet can help guard against aging and disease.

‍