What Is Oxidative Stress?
Oxidative stress is an imbalance between reactive oxygen species (free radicals) and your body's antioxidant defences. Your body produces free radicals during normal metabolism, and the production increases with exercise, pollution exposure, UV radiation, and other environmental factors. Antioxidant compounds, including those found in microalgae, participate in managing this balance at the biochemical level.
You will encounter this term frequently in algae supplement marketing, usually as claims that a product "reduces oxidative stress" or "fights free radicals." The underlying biochemistry is real and worth understanding. The consumer-facing claims built on top of it, however, frequently overstate what can be said responsibly.
No EFSA-authorised health claim permits stating that an algae supplement "reduces oxidative stress" as a health benefit. You can read more about how these boundaries work in our evidence hub.
Antioxidant Compounds in Microalgae
Marine phytoplankton from Nannochloropsis contains carotenoids (violaxanthin, beta-carotene) and chlorophyll, all of which have documented antioxidant activity in biochemical assays. Chlorella provides the highest chlorophyll concentration of any common food, plus lutein and beta-carotene. Spirulina contributes phycocyanin. We covered the compound differences in our Nannochloropsis nutrition profile.
These compounds are genuinely present and their antioxidant chemistry is well-established. The gap is between "this compound neutralises free radicals in a test tube" and "taking this supplement will measurably reduce oxidative stress in your body at the dose on the label." That gap is where we draw the line on what we claim for our products.
When we were finalising our Nannochloropsis label, violaxanthin was the compound we spent the most time on. We could measure its presence precisely at roughly 3.4 mg per gram of dry biomass, and the antioxidant chemistry in published assays is well-documented.
What we could not do is claim it reduces oxidative stress in you. So we list it as a naturally occurring carotenoid without attaching a health outcome — which is the honest position the evidence supports.
Oxidative Stress at a Glance
- What it is: Imbalance between free radical production and antioxidant capacity
- Normal causes: Metabolism, exercise, UV exposure, pollution, ageing
- Algae antioxidants: Carotenoids, chlorophyll, phycocyanin (documented biochemical activity)
- Regulatory status: No EFSA-authorised claim allows stating an algae supplement "reduces oxidative stress"
- The honest position: The compounds are present; the consumer health claims are not authorised
What our research found
Large-scale antioxidant supplement trials have found harm, not benefit. The CARET trial was terminated early after beta-carotene plus vitamin A caused a 28 per cent increase in lung cancer incidence in smokers. The SELECT trial found vitamin E supplementation increased prostate cancer risk. These were not marginal effects. They were significant enough to stop the studies.
The Cochrane review found no mortality benefit from antioxidant supplementation in healthy adults. Some antioxidant supplements may increase all-cause mortality slightly. The gap between a compound showing antioxidant activity in a test tube and that same compound improving health outcomes in your body is wider than supplement marketing suggests. This is why we do not make antioxidant health claims for our products.
Sources
Cara Hayes, MSc Nutrition and Dietetics (University of Sydney), writes all content in the Phytality Knowledge Centre. Read our editorial policy.
This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Consult your healthcare provider before starting any supplement.
Methodology and Disclosure
Phytality manufactures algae supplements containing antioxidant compounds. We have a commercial interest in these compounds being valued. Oxidative stress biochemistry reflects established cell biology. Antioxidant activity of carotenoids and chlorophyll reflects published chemistry. No EFSA-authorised health claims are cited for oxidative stress reduction from algae.
Last reviewed: March 2026
