Biochemistry
Antioxidants and free radicals explained
Antioxidants get marketed like a superpower. The biochemistry behind them is real — the supplement claims built on top of it mostly aren't.
What a free radical actually is
A free radical is a molecule with an unpaired electron, which makes it unstable and reactive. To stabilize itself, it steals an electron from a nearby molecule — DNA, a protein, a cell membrane lipid — which creates a new free radical and can trigger a damaging chain reaction. This process is called oxidative stress when it outpaces the body's ability to neutralize it.
Free radicals aren't purely a problem to eliminate: your immune cells deliberately generate them to destroy pathogens, and cell signaling relies on them in small amounts. The issue is excess, from sources like UV exposure, air pollution, smoking, and normal metabolic byproducts.
How antioxidants work
An antioxidant is a molecule that can donate an electron to a free radical without becoming unstable itself, ending the chain reaction. Vitamin C, vitamin E, beta-carotene, and selenium are the best-studied dietary antioxidants, alongside plant compounds like flavonoids and polyphenols found in berries, tea, and colorful vegetables.[1]
Why supplement trials disappointed
Despite strong observational links between antioxidant-rich diets and lower disease risk, large randomized trials of concentrated antioxidant supplements (particularly high-dose beta-carotene and vitamin E) have repeatedly failed to reduce disease risk, and in a few cases showed harm. The leading explanation: food-based antioxidants arrive alongside fiber, hundreds of other plant compounds, and a different absorption pattern than an isolated, concentrated pill — the whole-food package appears to matter, not just the isolated molecule.[1]
The practical takeaway most researchers converge on: get antioxidants from a varied diet of fruits, vegetables, nuts, and tea rather than from high-dose isolated supplements. See vitamin C and vitamin E's fat-soluble relatives for the individual nutrients.
Frequently asked questions
Do antioxidant supplements prevent disease?
Large randomized trials of concentrated antioxidant supplements, particularly high-dose beta-carotene and vitamin E, have generally failed to reduce disease risk despite strong observational links between antioxidant-rich diets and lower risk.
What is oxidative stress?
Oxidative stress occurs when free radicals — reactive molecules with an unpaired electron — outpace the body's ability to neutralize them, potentially damaging DNA, proteins, and cell membranes.
Are free radicals always bad?
No. Immune cells deliberately produce free radicals to destroy pathogens, and they play a role in normal cell signaling. Problems arise from excess, driven by sources like UV exposure, pollution, and smoking.
Keep reading: Vitamin C and immunity · Fiber and your gut microbiome · Ultra-processed foods