What Is Oxidative Stress — and What Does It Have to Do with Aging?
Oxidative stress is frequently described as something we should eliminate. The biology is more complicated.
Our cells naturally produce reactive molecules as part of normal metabolism. At controlled levels, these molecules are involved in essential processes, including cell signaling and immune responses.
The problem begins when their production persistently exceeds the body’s ability to control the resulting damage.
What exactly is oxidative stress?
Many reactions in the body produce molecules known as reactive oxygen species.
Some are generated by mitochondria as cells produce energy. Others are produced by enzymes involved in normal cellular functions and immune defense.
The body therefore has multiple systems that keep these reactive molecules under control. These include antioxidant defenses as well as mechanisms that repair or remove damaged cellular components.
Oxidative stress develops when the balance shifts toward excessive oxidant activity and the body’s protective systems can no longer compensate adequately.
This can increase damage to DNA, proteins and lipids — important components of our cells.
Why does oxidative stress increase with age?
Aging affects many of the systems responsible for maintaining cellular stability.
Mitochondria may become less efficient. Cellular repair and recycling mechanisms can decline. Chronic low-grade inflammation can increase, while damaged and senescent cells may accumulate.
These processes can increase oxidative stress.
At the same time, oxidative damage can further impair mitochondria, DNA and cellular repair systems.
This means oxidative stress can become part of a biological feedback loop involving cellular damage, inflammation and declining resilience.
Where does the environment fit in?
Oxidative stress can arise from processes inside the body, but external exposures can add to this burden.
Research has shown that air pollution, certain metals, pesticides and other environmental pollutants can promote reactive oxygen species through several different mechanisms.
For example, some pollutants can interfere with mitochondrial function. Others can activate inflammatory cells or participate directly in chemical reactions that generate reactive molecules.
This is one reason oxidative stress is being studied as a possible biological link between environmental exposure and aging-related disease.
Does oxidative stress cause aging?
Oxidative stress is clearly involved in many biological processes associated with aging. But aging cannot be reduced to oxidative stress alone.
Human aging involves interacting changes in mitochondrial function, DNA repair, immune regulation, metabolism, cellular senescence, epigenetic regulation and many other systems.
Oxidative stress can influence several of these pathways, and these pathways can in turn influence oxidative stress.
It is therefore better understood as one interconnected component of aging biology, rather than a single explanation for why we age.
Does taking antioxidants slow aging?
This is where a plausible biological idea can easily become an exaggerated health claim.
If excessive oxidative stress can damage cells, it may seem logical that taking more antioxidants should slow aging.
Human biology is not that simple.
Reactive oxygen species also perform important physiological functions. Completely suppressing them would neither be possible nor desirable.
More importantly, evidence that a substance has antioxidant activity does not establish that taking it as a supplement slows biological aging or extends healthy lifespan in humans.
Clinical studies of antioxidant supplementation have produced inconsistent results, and the effect depends on the antioxidant, dose, population and health outcome being studied.
For healthy aging, an “antioxidant” label alone is therefore not evidence of an anti-aging effect.
Can oxidative stress be measured?
It can be assessed indirectly by measuring products of oxidative damage or aspects of the body’s redox balance.
Examples include markers of lipid oxidation, oxidative DNA damage and antioxidant systems.
But oxidative stress is a dynamic biological process. There is currently no single laboratory test that provides a complete measurement of a person’s total oxidative stress or tells us how quickly that person is aging.
This is why oxidative-stress biomarkers need to be interpreted according to what they actually measure rather than treated as general biological-age tests.
