Antioxidant supplement UK: what the evidence shows

The antioxidant supplement market in the UK is worth hundreds of millions of pounds annually — and a fair chunk of that money is spent on products with shakier evidence than their labels suggest. Some antioxidants have solid human trial data behind them. Others have compelling animal or in-vitro research that hasn't yet translated to meaningful outcomes in people. This piece tries to separate the two, honestly, with numbers where they exist.

What the evidence actually shows

Let's start with the headline finding that most antioxidant marketing ignores: blanket antioxidant supplementation in healthy people does not have a strong track record in large randomised controlled trials. That's not a fringe view — it's the consensus that emerged after several major trials in the 1990s and 2000s showed null or even adverse effects from high-dose beta-carotene and vitamin E.

That said, the picture is more nuanced than "antioxidants don't work." Context matters enormously. In populations with documented deficiency, or in specific clinical conditions where oxidative stress plays a measurable role, certain antioxidants do show meaningful effects. Evans et al. (2023) reviewed antioxidant vitamin and mineral supplements for macular degeneration associated with ageing and found that a specific combination — vitamin C, vitamin E, beta-carotene, and zinc — may reduce progression to advanced AMD by around 25% in people already at moderate-to-high risk. That's a targeted population with a specific pathology, not a general wellness claim.

Similarly, Amini et al. (2021) found that combined vitamin C and vitamin E supplementation may reduce markers of oxidative stress in women with endometriosis — a condition characterised by elevated reactive oxygen species in peritoneal fluid. The effect was real, but again: specific population, specific condition, specific markers.

The takeaway I keep coming back to is this: antioxidants aren't a category you can evaluate wholesale. You have to look at which antioxidant, at what dose, in which population, measured against which outcome. Anything less than that is marketing.

The biology: what oxidative stress actually is

Reactive oxygen species (ROS) are produced as a normal byproduct of cellular metabolism — particularly in the mitochondria during ATP synthesis. At low concentrations, ROS serve signalling functions. They help regulate immune responses, trigger cellular repair pathways, and mediate adaptation to exercise. The problem arises when ROS production outpaces the body's endogenous antioxidant capacity — enzymes like superoxide dismutase, catalase, and glutathione peroxidase.

This imbalance — more ROS than the endogenous systems can neutralise — is what oxidative stress refers to. It can damage lipids, proteins, and DNA. Chronically elevated oxidative stress is associated with a range of conditions, though "associated with" is doing a lot of work in that sentence. Correlation in observational data doesn't tell anyone that supplementing with exogenous antioxidants will reverse the process, especially if the underlying driver of ROS production hasn't been addressed.

Vitamin C is a water-soluble antioxidant that donates electrons to neutralise free radicals directly. It also regenerates vitamin E — a fat-soluble antioxidant — after vitamin E has been oxidised. This is why the combination appears more effective than either alone in some studies. Vitamin C contributes to the protection of cells from oxidative stress — this is a registered UK/EU health claim, and one I think is genuinely well-supported by the mechanistic and clinical literature.

Polyphenols like those found in grape seed, pine bark, and olive leaf work somewhat differently. They don't just scavenge free radicals directly — they appear to upregulate endogenous antioxidant enzyme activity via the Nrf2 pathway, a transcription factor that switches on genes encoding antioxidant proteins. The human data on this is thinner than the mechanistic data, and I'd be overstating it to claim there is definitive RCT evidence for clinical outcomes from these compounds in healthy adults.

Which antioxidants have the strongest human evidence

Vitamin C

Vitamin C is the one I feel most confident about, partly because the evidence base is large and partly because the registered health claims are genuinely earned. Vitamin C contributes to the normal function of the immune system — that's not marketing language, it's a claim that required regulatory scrutiny to get approved. At 500mg daily (the dose in KōJō Daily Formula), you're well within the range studied in clinical trials and comfortably below the tolerable upper intake level of around 2,000mg/day.

Czajka et al. (2019) looked at daily supplementation combining collagen peptides with vitamin C and other bioactive compounds and found statistically significant improvements in skin elasticity and hydration over 12 weeks — relevant here because vitamin C contributes to normal collagen formation for the normal function of skin. The multi-ingredient design makes it hard to isolate vitamin C's contribution, but the mechanistic rationale is solid.

Polyphenol complexes

Grape seed extract, pine bark extract, and olive leaf extract are studied for their polyphenol content — primarily oligomeric proanthocyanidins and oleuropein respectively. The research is ongoing, and large-scale human trials are limited, so I'm careful about what I claim here. What I can say is that the mechanistic pathways are plausible and the safety profile in short-term studies looks acceptable. Whether the effect sizes in small trials will replicate in larger ones remains an open question.

Ubiquinol

Ubiquinol is the reduced, active form of coenzyme Q10. It plays a direct role in the mitochondrial electron transport chain and also functions as a lipid-soluble antioxidant. Research into ubiquinol is ongoing, and while some smaller studies show promise — particularly in populations with statin-induced CoQ10 depletion — large-scale human trials confirming clinical outcomes in healthy adults are still limited.

What clinical dosing data actually supports

This is where a lot of supplement products fall down. They include an ingredient at a dose that looks impressive on a label but bears no relationship to the doses used in published trials.

For vitamin C, the range studied in immune-related trials is typically 200–1,000mg/day. The 500mg in KōJō Daily Formula sits in the middle of that range. For context, the UK RDA is just 40mg — enough to prevent deficiency, but likely insufficient for the antioxidant and immune-support effects studied in RCTs.

For polyphenols, the picture is messier. Grape seed extract trials have used doses ranging from 100mg to 400mg/day. Pine bark extract (Pycnogenol) has been studied at 50–200mg/day. Olive leaf extract trials vary widely — 500mg of a standardised extract is at the higher end of what's been used. The honest answer is that optimal dosing for these compounds in healthy adults hasn't been established, because there aren't yet enough high-quality RCTs to draw firm conclusions.

Aged garlic extract is a slightly different case. It's been studied for cardiovascular markers, immune cell activity, and oxidative stress. Doses in trials typically range from 600mg to 2,400mg/day of aged garlic extract. Research into aged garlic is ongoing, and large-scale human trials are limited — but 600mg is consistent with the lower end of the range that has appeared in published work.

For taurine and glycine — both present in KōJō's formula — these are amino acids with antioxidant-adjacent properties rather than classical antioxidants. Taurine may help protect cells from oxidative damage via taurine chloramine formation, though the human data on this is thin and I'd be overstating it to claim a primary antioxidant role. Research into glycine's role in oxidative stress is ongoing, and large-scale human trials are limited.

Antioxidants and immune function: what's the connection

The immune system is metabolically expensive. Activated immune cells — particularly neutrophils and macrophages — deliberately generate large quantities of ROS as part of their pathogen-killing arsenal. This is called the oxidative burst, and it's essential for immune defence. But it also means immune tissue is chronically exposed to high ROS concentrations and needs strong antioxidant protection to avoid collateral damage.

Vitamin C concentrates in immune cells at levels up to 80-fold higher than plasma concentrations. This isn't coincidence. The evidence suggests vitamin C may support neutrophil function, lymphocyte proliferation, and antibody production — all mechanistically plausible given its role in reducing oxidative stress in those cells. Vitamin C contributes to the normal function of the immune system is, in this context, a claim I find well-grounded.

If you want to read more about how specific nutrients interact with immune pathways, I've written about this in more depth in my piece on supplement for immune system uk what actually works — worth reading alongside this one.

There's also an interesting stress angle here. Chronic psychological stress drives cortisol elevation, which in turn suppresses certain immune functions and may increase oxidative stress markers. I've covered the sleep and cortisol side of this in cortisol insomnia what the evidence shows — because if you're not sleeping, no antioxidant supplement is going to compensate.

What the exercise research adds

Exercise is one of the most reliable ways to acutely raise ROS production — and one of the most studied contexts for antioxidant supplementation. The findings here are genuinely interesting, and slightly counterintuitive.

Naderi et al. (2025) reviewed nutritional strategies for post-exercise recovery and noted that while antioxidants may help manage exercise-induced oxidative stress, high-dose antioxidant supplementation around training may actually blunt some of the adaptive signalling that makes exercise beneficial. ROS aren't purely harmful — they're part of the signal that tells your body to adapt.

Nanavati et al. (2022) reviewed curcumin supplementation for exercise-induced muscle damage and found that it may reduce markers of muscle damage and inflammation following eccentric exercise, though the authors noted significant heterogeneity across studies and called for larger RCTs. The effect sizes reported varied widely — from modest to negligible — depending on the population and protocol.

Tipton (2016) reviewed nutritional support for exercise-induced injuries and noted that antioxidant nutrients may support tissue repair processes, though the evidence for specific supplementation protocols in injured athletes remained limited at the time of writing.

My read: if you're training hard, moderate antioxidant intake from food and supplementation probably makes sense. Megadosing antioxidants around workouts is probably counterproductive. The sweet spot is somewhere in the middle — which is, conveniently, where most evidence-based formulas land.

The UK regulatory picture: what you can and can't claim

This matters more than most people realise when shopping for an antioxidant supplement in the UK. Post-Brexit, the UK retains the EU Nutrition and Health Claims Register for authorised claims — meaning a supplement brand can only make specific health claims if those claims have been approved by EFSA and are on the register.

"Vitamin C contributes to the protection of cells from oxidative stress" is an authorised claim. "This product fights free radicals and supports your body's defences" is not — at least not without the former underpinning it. When you're evaluating products, look for claims that map to the register. If a brand is making vague promises about "cellular protection" without citing the specific registered claim, that's a yellow flag.

I've written more about how to evaluate immune supplement evidence specifically in immune support supplement what the evidence shows — including how to read labels and spot the difference between registered claims and marketing copy.

Antioxidants and skin: a specific use case worth noting

One area where the antioxidant evidence is reasonably solid — and where I think supplementation makes genuine sense — is skin health, specifically via vitamin C's role in collagen synthesis. Vitamin C contributes to normal collagen formation for the normal function of skin. That's a registered claim, and the mechanistic basis is well-established: vitamin C is a required cofactor for prolyl and lysyl hydroxylase, the enzymes that stabilise collagen's triple helix structure.

UV radiation generates ROS in skin tissue, and vitamin C's antioxidant function in this context is well-studied. Czajka et al. (2019) showed that a combination supplement including vitamin C was associated with measurable improvements in skin elasticity and hydration at 12 weeks in a sample of 120 women. The multi-ingredient design is a limitation, but the findings are consistent with mechanistic expectations.

Evans et al. (2023) also noted that antioxidant combinations may slow progression of oxidative damage in eye tissue — another tissue with high metabolic activity and chronic ROS exposure. The AMD data is probably the strongest specific clinical evidence available for antioxidant supplementation in any condition.

Frequently asked questions

My honest take

I started KōJō partly out of frustration with how antioxidants are marketed in the UK. The category has been used to sell everything from overpriced berry powders to capsules with trace amounts of ingredients that wouldn't move a needle in any study I've read. That frustrates me — not because antioxidants don't matter, but because the lazy marketing obscures the cases where they genuinely do.

Vitamin C at a meaningful dose, in a clean form, is probably the most evidence-backed antioxidant supplement you can take. The registered health claims exist for a reason. The mechanistic data is solid. The clinical trial record — while imperfect — is more consistent than almost anything else in this category.

For polyphenols — grape seed, pine bark, olive leaf, aged garlic — I'm genuinely interested in the science. The Nrf2 pathway research is compelling. Some of the smaller trials are encouraging. But I try to be honest with myself: there's no large-scale RCT evidence to point to for most of these compounds in healthy adults, and I'm not going to pretend otherwise. They're in KōJō's formula because the mechanistic rationale is sound and the safety data is acceptable — not because I can promise you a specific clinical outcome.

The thing I'd push back on most in the antioxidant supplement space is the idea that more is always better. The exercise research in particular suggests that flooding your system with antioxidants can interfere with the very adaptive processes you're trying to support. A moderate, evidence-informed dose — not a megadose — is almost certainly the right approach.

If you want to see exactly what's in the formula and at what doses, the KōJō Daily Formula page has every ingredient listed with its dose. No hidden blends. That's the standard every supplement brand in the UK should be held to — and mostly isn't.

This article is for informational purposes only and does not constitute medical advice. Consult your healthcare provider before starting any supplement regimen.

References (10 studies)

1. Naderi et al. (2025) — Nutritional Strategies to Improve Post-exercise Recovery and Subsequent Exercise Performance: A Narrative Review. PMID 40221559.
2. Tipton (2016) — Nutritional Support for Exercise-Induced Injuries. PMID 26553492.
3. Amini et al. (2021) — The Effect of Combined Vitamin C and Vitamin E Supplementation on Oxidative Stress Markers in Women with Endometriosis. PMID 34122682.
4. Evans et al. (2023) — Antioxidant vitamin and mineral supplements for slowing the progression of age-related macular degeneration. PMID 37702300.
5. Nanavati et al. (2022) — Effect of curcumin supplementation on exercise-induced muscle damage: a narrative review. PMID 35831667.
6. Czajka et al. (2019) — Daily oral supplementation with collagen peptides combined with vitamins and other bioactive compounds improves skin elasticity and hydration. PMID 30122200.
7. Borodina et al. (2021) — The biology of ergothioneine, an antioxidant nutraceutical. PMID 32051057.
8. Yu et al. (2024) — Gut microbiota and ageing: Focusing on spermidine. PMID 37326367.
9. Teparak et al. (2025) — Diabetes Therapeutics of Prebiotic Soluble Dietary Fibre and Antioxidant Anthocyanin Supplement in Patients with Type 2 Diabetes. PMID 40218856.
10. Zare et al. (2024) — Effect of Soy Protein Supplementation on Muscle Adaptations, Metabolic and Antioxidant Status, Hormonal Response, and Exercise Performance. PMID 37603200.

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