What are free radicals and what do they do to your cells?
Free radicals are unavoidable and even useful, but too many of them damage your cells. Large doses of antioxidant supplements do not help with that, however tempting the idea may be.
Every cell in your body continuously produces energy, and that process does not come without by-products. About 5% of the oxygen your cells burn is not converted into water and energy but into free radicals, also known as reactive oxygen species. They are therefore not an accident, but an inevitable consequence of life itself.
Free radicals are unstable molecules that cause damage to the three main building blocks of your cells: DNA, fats in cell membranes, and proteins. Damage to DNA is the most critical point among these, because it can be a first step toward diseases such as cancer.
But free radicals are not purely negative. Your immune system actively uses them to kill invaders, and they function as signalling molecules through which cells communicate with one another. They are therefore a double-edged sword: useful in small amounts, dangerous when they gain the upper hand.
That dangerous imbalance is called oxidative stress: more free radicals are produced than your body can clear away. This is linked to diabetes, atherosclerosis, cancer, and brain diseases such as Alzheimer's and Parkinson's. How strongly free radicals causally contribute differs from disease to disease, but the associations have been found repeatedly. External factors such as exhaust fumes, UV radiation, and certain medications increase production further, with the skin being particularly vulnerable as the body's outermost organ. During severe infections, iron that has been released into the blood can also worsen the damage by generating especially aggressive free radicals.
The intuitive idea that you can simply stop oxidative stress with antioxidant supplements is not correct. Clinical studies with high doses of vitamin E, vitamin C, and beta-carotene show no convincing benefit in preventing or treating chronic diseases. Taking large quantities of antioxidant supplements is therefore not proven to be effective, even though it seems intuitively sensible.
Based on multiple review studies and clinical literature (PMID 34639139, 39031349, 16430879, 36344150, 25310939, 7922395). The basic biology of free radicals is solidly supported; the causal role in specific diseases is plausible but variably proven depending on the condition. The lack of effect of antioxidant supplements is based on clinical studies, but the precise mechanism behind that failure has not yet been fully elucidated.