Oxidative stress

What does oxidative stress actually mean?

Cells naturally produce reactive oxygen compounds. When production overwhelms protective processes, these compounds can damage cells; this is oxidative stress. Antioxidant enzymes are part of the body’s own defenses. 1

Free radicals are not simply unwanted waste. They arise during normal cell activity, while high concentrations can harm DNA, proteins and cell membranes. Cigarette smoke, radiation and certain environmental exposures can increase their formation. 2

What does an antioxidant test measure?

Researchers measure reactive molecules or the products they leave behind. These molecules are short-lived and difficult to measure accurately, and different tests have different strengths and limitations. An “oxidative stress” result therefore needs the name of the marker and the method behind it. 3

Can it explain feeling unwell?

Fatigue has many possible causes, including poor sleep, stress, medicines and illness. Persistent unexplained tiredness deserves assessment on its own terms, rather than an assumed need for antioxidants. 4

Which supplements change laboratory markers?

The following reviews evaluated biochemical markers. Their results answer a narrower question than whether a supplement prevents disease or improves daily well-being. 5 6

Coenzyme Q10Too little evidence

A 2020 meta-analysis of 19 studies found higher total antioxidant capacity and lower malondialdehyde, a marker of oxidative damage to fats. Several antioxidant enzymes also increased. Publication-bias concerns affected some enzyme results; these findings alone do not establish a clinical benefit. 5

CurcuminToo little evidence

A 2020 meta-analysis included four trials with 308 participants. Total antioxidant capacity increased, but the reduction in malondialdehyde was not statistically significant. That combination is a useful reminder that different markers need not tell the same story. 6

Does antioxidant supplementation prevent disease?

For generally healthy, nonpregnant adults without known deficiencies, the US Preventive Services Task Force recommends against vitamin E or beta-carotene supplements to prevent cardiovascular disease or cancer. Evidence was insufficient for most other vitamin or mineral supplements for these purposes. 7

Vitamin ENot supported

The prevention trials do not support using vitamin E for cardiovascular disease or cancer prevention in this population. 7

Beta-caroteneNot supported

Beyond the lack of preventive benefit, beta-carotene supplements increase lung-cancer risk in people who smoke or have occupational asbestos exposure. 7

Why food and pills are different questions

Fruit and vegetable intake is associated with better health in observational research. That does not identify isolated antioxidants as the cause: foods contain many substances. More antioxidant activity is not automatically better, because reactive molecules also participate in normal signaling and defense. 1

Concentrated extracts need their own safety check

EFSA found signs of liver injury at supplemental intakes of 800 mg of the green-tea compound EGCG daily or more. It could not establish a safe supplemental dose below that level. Traditional green-tea infusions were generally considered safe, although rare liver reactions have occurred. 8

CoQ10 can interact with warfarin and insulin and may be incompatible with some cancer treatments. Digestive upset and insomnia are reported side effects. 9

Scope of this review

This page reviews the supplements above, not every substance marketed as an antioxidant.

Questions people ask