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For horses · Aug 30, 2016

Rooibos belongs in the feed room, and the science shows why

Its key flavonoid aspalathin, unique to rooibos and found nowhere else in nature, supports antioxidant defence, calms inflammation, and helps keep stress hormones in cheque.

Bay horse at stable door with dried rooibos on the feed shelf — antioxidant herb for horses

By Beryl Shuttleworth, BSc Hons Biochem

Last reviewed: 2026-07-22

Rooibos (*Aspalathus linearis*) is one of the better-evidenced antioxidant herbs we have. Its key active compound, aspalathin, a flavonoid found in no other plant on earth, scavenges free radicals about as effectively as EGCG, the antioxidant that makes green tea famous. It doesn’t rely on a single trick: rooibos works through several different pathways: direct radical scavenging, slowing lipid peroxidation, boosting the body’s own protective enzymes (catalase, superoxide dismutase, glutathione peroxidase), and even dampening cortisol production by acting on adrenal enzymes. There are no controlled trials in horses yet, but the mechanisms involved are not unique to any one species.

Common misconception: Rooibos is just a gentle antioxidant tea, the benefits are all about mopping up free radicals

It’s easy to see why this idea sticks. Rooibos is marketed almost entirely on its antioxidant credentials, and the free-radical story is a simple one to tell. It’s also partly true, aspalathin and nothofagin really are potent radical scavengers, and in lab studies aspalathin matches EGCG (the benchmark antioxidant from green tea) in terms of radical-quenching strength [2, 12]. But if you stop there, you’re missing most of what rooibos actually does.

Even the antioxidant side is more layered than it first appears. Rooibos doesn’t just mop up free radicals directly, it also helps the body produce its own protective enzymes, including catalase, superoxide dismutase, and glutathione peroxidase, and it helps restore glutathione levels when they’ve been depleted by stress or injury [3, 4]. Aspalathin in particular works by switching on the Nrf2 pathway, think of this as the body’s internal antioxidant control switch, which ramps up production of several protective genes, including catalase (by nearly 12-fold) and Gpx2 (by nearly 16-fold) [5]. That’s quite different from simply neutralising a free radical.

Beyond oxidative stress, rooibos has effects in other areas entirely. Research shows it can dampen inflammatory signals, including TNF-α, IL-6, IL-1β, and IL-8, in models of liver injury and fat-tissue inflammation [3, 19]. It also influences the way the body handles stress hormones, by affecting enzymes involved in cortisol metabolism, with measurable reductions in cortisol and corticosterone seen in animal studies [6, 7]. And there’s early in vitro evidence that it can help support the integrity of the gut lining, affecting proteins that hold intestinal cells together, independently of how much of it is actually absorbed into the bloodstream [22].

So rooibos is not simply a soothing cup with a few antioxidants in it. It works through several distinct biological pathways, it just happens to have been boxed in by marketing that only tells half the story.

How rooibos works: Antioxidant, anti-inflammatory, and stress-hormone mechanisms

Rooibos (*Aspalathus linearis*) works through several distinct pathways, all rooted in its unusual flavonoid profile.

Aspalathin is the standout compound, a type of plant polyphenol called a dihydrochalcone C-glycoside, and it genuinely doesn’t exist in any other plant on earth. In laboratory tests, it neutralises harmful free radicals about as effectively as epigallocatechin gallate (EGCG), the antioxidant that makes green tea famous. Alongside aspalathin, nothofagin, quercetin, and catechin add to rooibos’s antioxidant repertoire, with quercetin and catechin specifically helping to prevent damage to cell membranes from oxidised fats.

Three antioxidant mechanisms work at the same time. The first is direct free-radical scavenging, aspalathin and nothofagin mop up reactive molecules in a similar way to vitamins C and E. The second is slowing down lipid peroxidation, which matters because oxidised fats in cell membranes are a key driver of tissue damage. The third, and the one I find most significant, is that rooibos encourages the body to produce more of its own protective enzymes: superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPx). In rat studies involving both liver injury and acute stress, rooibos restored these enzyme levels and helped recover glutathione (GSH), one of the body’s most important natural antioxidants. The Nrf2 pathway sits at the heart of this, think of Nrf2 as a master switch that, when activated by aspalathin, turns on a whole suite of protective genes, including catalase, Gpx2, SOD1, and SOD2, at very low concentrations (1 µM).

For inflammation, rooibos reduced pro-inflammatory signalling molecules, TNF-α and IL-6, in rat models of liver injury triggered by bacterial toxin. In separate cell-based studies, it also lowered a broader panel of inflammatory markers (IFN-γ, IL-12, IL-2, IL-17a, IL-8, IL-1β, and CXCL10) and calmed the type of immune cell activity most associated with tissue inflammation.

For stress hormones, rooibos appears to act on the machinery that regulates cortisol. In laboratory studies it inhibited an enzyme called 11β-hydroxysteroid dehydrogenase type 1 (11βHSD1), which is responsible for converting inactive cortisone back into active cortisol. That gives a plausible explanation for why rooibos consumption reduced cortisol:cortisone ratios in human subjects. In adrenal cell studies, rooibos and its dihydrochalcones also directly dialled down two other enzymes in the cortisol-production pathway, CYP17A1 and CYP21A2, reducing cortisol output from stimulated adrenal cells.

How to use rooibos for horses: What the evidence actually supports

Form and administration
No brewing required, simply add loose rooibos straight to your horse’s feed. Most horses take to it well; it has a naturally sweet, pleasant smell that tends to go down without a fuss. The active flavonoids, including the unique compound aspalathin found only in rooibos (Aspalathus linearis), are already present in the dried herb.

Duration and long-term use
For most horses at sensible, food-appropriate amounts, the research picture is reassuring. In rodent studies, rooibos reversed markers of chemically induced liver damage, including fatty liver and scarring, to a degree comparable to N-acetyl-L-cysteine, a well-regarded antioxidant support agent.

That said, rat studies running 28 and 90 days at very high, aspalathin-enriched doses did show some shifts in the liver’s glutathione balance over time, a key part of how the body manages oxidative stress. Glutathione reductase activity went up at 28 days, while overall glutathione levels had fallen by 90 days. It’s not a reason to avoid rooibos, but it is a reason not to pile in at very high doses indefinitely. How this plays out in horses specifically hasn’t been studied.

When to be cautious
Rooibos flavonoids interact with two enzymes in the adrenal glands, CYP17A1 and CYP21A2, that are involved in producing cortisol and related stress hormones. In both rat and human studies, rooibos consumption measurably shifted cortisol and corticosterone levels. For a horse under stress, that’s actually part of the appeal.

But it does mean rooibos isn’t a neutral addition if your horse is already on steroid-based medication, or if they have a diagnosed hormonal condition such as pituitary pars intermedia dysfunction (PPID). The interaction isn’t theoretical, it’s documented at an enzymatic level. There’s no equine-specific contraindication research to draw on, but the mechanism is clear enough that I’d always recommend a conversation with your vet before supplementing in those circumstances.

What we’d recommend


Herbal Horse Digestion mix

Rooibos in this blend helps horses manage everyday oxidative stress, inflammation, digestion and stress naturally.

See product.

Frequently asked questions

What makes rooibos different from other antioxidant herbs for horses?

Rooibos contains aspalathin, a flavonoid found in absolutely no other plant on earth. In lab studies, it scavenges free radicals about as powerfully as the well-known green tea antioxidant EGCG. What I find particularly interesting is that rooibos doesn’t rely on a single trick, it works through several antioxidant pathways at once: mopping up free radicals directly, slowing lipid peroxidation, and encouraging the horse’s own body to produce more of its natural protective enzymes, including catalase and superoxide dismutase.

Can rooibos help horses with stress or high cortisol?

The evidence suggests it can help regulate the stress hormone system, and the mechanism is reasonably well understood. Rooibos appears to slow down an enzyme called 11βHSD1, which would otherwise convert inactive cortisone back into active cortisol, essentially putting a brake on cortisol recycling. It also dampens activity in the adrenal glands themselves, where cortisol is made in the first place. In rat studies, stress hormone levels fell with regular rooibos consumption. We don’t yet have equivalent data for horses, but the underlying biology is consistent.

Does rooibos protect the liver?

In two separate rat studies, one using a bacterial toxin to trigger liver injury, one using a harsh chemical called CCl₄, rooibos consistently reduced markers of liver damage. It brought down oxidative stress, helped restore the liver’s natural glutathione defences, calmed inflammatory signalling, and reversed raised levels of liver enzymes ALT, AST, and alkaline phosphatase. The effects were comparable to N-acetyl-L-cysteine, a pharmaceutical liver-support agent. We don’t have horse-specific dose data yet, but the hepatoprotective pattern holds across different study models.

Is rooibos anti-inflammatory as well as antioxidant?

Yes, and it’s worth being clear that these are two separate but connected actions. Lab and rat studies show rooibos reduces a broad range of inflammatory messenger molecules, including TNFα, IL-6, IL-1β, IL-8, IFN-γ, and several others, and appears to calm the type of immune activity most associated with tissue damage. This matters because oxidative stress and inflammation tend to drive each other in a cycle; an ingredient that addresses both simultaneously is more useful than one that only tackles one side. Human clinical evidence at real-world doses is still limited, but the mechanistic picture is consistent.

Sources

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