Antioxidants

What antioxidants actually do

Antioxidants are molecules that neutralize reactive oxygen species (ROS), unstable compounds your cells produce constantly as a byproduct of mitochondrial energy metabolism. In small amounts, ROS function as signaling molecules that trigger repair and adaptation. The problem starts when ROS production outpaces your body's ability to clear them. This imbalance, called oxidative stress, damages DNA, proteins, and cell membranes, and it accelerates biological aging. Denham Harman proposed the free radical theory of aging in 1956, and while the picture has gotten more complex since then, the core insight holds: chronic, uncontrolled oxidative damage shortens healthspan ^[1].

Your body's built-in antioxidant defenses

Before reaching for a supplement bottle, it's worth understanding what your body already has in place. Glutathione is the most important endogenous antioxidant. It's a tripeptide made in every cell, and it handles detoxification, immune support, and recycling of vitamins C and E. Superoxide dismutase (SOD) converts superoxide radicals into hydrogen peroxide, which catalase then breaks down into water. These enzymes are the first line of defense.

The Nrf2 pathway ties it all together. When oxidative stress rises, Nrf2 activates hundreds of protective genes that ramp up antioxidant enzyme production, detoxification, and cellular repair ^[2]. Many polyphenols from food work through this pathway rather than by directly scavenging free radicals. They create a mild oxidative signal that triggers a disproportionately strong defensive response, a process called hormesis. This is why eating colorful plant foods consistently outperforms popping isolated antioxidant pills in clinical research ^[3].

Polyphenols and how they protect cells

Polyphenols are plant compounds found in berries, green tea, coffee, dark chocolate, olive oil, and spices. The major subclasses include flavonoids (quercetin, catechins, anthocyanins), stilbenes (resveratrol), phenolic acids (chlorogenic acid), and lignans (from flaxseed). What makes polyphenols interesting is their dual mechanism: they act as direct radical scavengers at high concentrations, but at the lower concentrations achieved through normal eating, they primarily work by activating Nrf2 and other adaptive stress pathways ^[2]. A 2025 review confirmed that dietary polyphenols reduce markers of inflammation and oxidative stress across multiple organ systems ^[4].

Antioxidant-rich foods vs. supplements

The evidence on this point is clear. Large randomized trials consistently show that whole foods rich in antioxidants reduce disease risk, while isolated high-dose supplements often don't, and sometimes cause harm. The SELECT trial found that high-dose vitamin E increased prostate cancer risk by 17% ^[5]. The ATBC and CARET trials showed that beta-carotene supplements raised lung cancer rates in smokers by 20% ^[6]. The problem isn't the antioxidants themselves. It's that mega-doses of single compounds disrupt the finely tuned redox balance your cells depend on.

The foods with the strongest evidence include blueberries, blackberries, strawberries, dark leafy greens, cruciferous vegetables, green tea, coffee, turmeric, dark chocolate (70%+ cacao), and extra virgin olive oil. Eating a variety matters more than chasing any single "superfood" because different antioxidants protect different tissues and recycle each other.

When supplements make sense

A few targeted antioxidant supplements have solid evidence behind them, particularly for people who can't get enough from diet alone:

• N-acetylcysteine (NAC) is a well-studied glutathione precursor. A 2024 meta-analysis of 26 studies found it significantly increases total antioxidant capacity and reduces inflammatory markers like IL-6 ^[7]
• Astaxanthin, a carotenoid from microalgae, has 100-500 times the radical-scavenging capacity of vitamin E. Clinical trials show benefits for skin health, joint inflammation, and CRP reduction at doses of 4-12 mg daily ^[8]
• Alpha-lipoic acid is both water- and fat-soluble, letting it work throughout the cell. It recycles vitamins C and E and regenerates glutathione

Antioxidants and exercise: a tricky relationship

This is where many people get the dosing wrong. Exercise generates a burst of ROS in working muscles. That burst isn't damage; it's a training signal. It activates PGC-1alpha, which drives mitochondrial biogenesis, and it improves insulin sensitivity through ROS-dependent pathways. A landmark PNAS study showed that vitamin C and E supplements taken around training sessions blocked these adaptations entirely ^[9]. A 2024 meta-analysis added nuance: in older adults, antioxidants combined with exercise may actually enhance muscle strength, possibly because aging muscles have less capacity to handle oxidative stress on their own ^[10]. The practical takeaway: if you're young and training hard, skip antioxidant supplements in the hours around exercise. If you're over 65, the calculation may be different.