oxidative stress
Meaning of oxidative stress: Not simply a shortage of antioxidants but a balance tipped the wrong way, with damage as the result rather than the cause.
Definition of oxidative stress
Oxidative stress is an imbalance inside cells between reactive oxygen molecules, which are produced constantly as a byproduct of using oxygen for energy, and the defenses that neutralize them. When production outpaces those defenses, the surplus molecules react with fats, proteins and DNA and damage them. The imbalance is a feature of aging and of many chronic diseases.
What are the molecules that do the damage?
Cells burn fuel using oxygen, and a small fraction of that oxygen ends up as unstable byproducts known as reactive oxygen species. These are not purely harmful. The immune system makes them deliberately to kill bacteria, and cells use them as internal signals. Trouble begins when they accumulate, because an unstable molecule steals an electron from whatever it meets, leaving that molecule unstable in turn and setting off a chain reaction through the fatty layer of the plasma membrane.
What keeps them in check?
A layered defense. Enzymes made by the cell itself convert the most reactive species into water in two quick steps. Small molecules absorbed from food, including vitamin C and vitamin E, mop up what escapes. Repair systems then fix what still gets through, replacing oxidized fats and clipping altered bases out of DNA. Taking extra antioxidant supplements does not reliably strengthen this system, and large trials of high-dose supplements have not reproduced the benefit the simple picture predicted.
What is damaged, and what follows?
| Target | Result of the damage |
|---|---|
| Cell membranes | Fats break down, so the membrane leaks |
| Proteins | Shape changes, so enzymes stop working |
| DNA | Altered bases, which become mutations if unrepaired |
| Mitochondria | Energy output falls and more byproducts are made |
Why is it hard to measure?
There is no single test. Laboratories measure indirect markers instead: breakdown products of oxidized fat, altered DNA bases in urine, or the activity of the protective enzymes. Each captures a fragment of the picture, and results shift with diet, exercise and time of day. That is why the older idea that the state can be read off a single antioxidant level in blood plasma does not hold. Oxidative metabolism generates these byproducts continuously, so the question is never whether they are present but whether the balance has tipped.
Also known as
Used in a sentence
Markers of oxidative stress were elevated in the affected tissue samples.
Good to know
The term describes a balance rather than a level, so a normal antioxidant reading in blood does not exclude it, and supplements have not consistently reproduced the benefits associated with antioxidant-rich diets.
Word origin
Where “oxidative stress” comes from
Oxidative comes from oxygen, a name built from the Greek oxys, meaning sharp or acid, with the ending -genes, meaning born of, from the early belief that oxygen formed acids.