Rooibos – What Scientists Are Studying
From plant compounds and flavour profiles to gut research and studies involving people.
At a glance
What do scientists study about rooibos? Researchers investigate which compounds the South African plant Aspalathus linearis produces, how cultivation and processing change its composition, and which biological processes rooibos constituents may influence in experiments. They also examine what can actually be measured in the human body after drinking rooibos.
These are different questions, and they require different types of investigation. What makes the research particularly interesting is how one discovery leads to the next: a plant compound is identified in the leaf, changes during processing, and can then be studied in cell models, microorganisms or a human trial.
Understanding the plant
What makes rooibos distinctive in terms of its chemistry and flavour? What changes during harvesting, oxidation and storage?
Investigating biological processes
How do cells, intestinal tissue or microorganisms respond under precisely controlled experimental conditions?
Studying people
Which compounds or changes can be measured after consumption, and how reliable are the findings?
Understanding the context
Why are scientists interested in rooibos?
Rooibos interests researchers for several reasons. The plant grows in a landscape shaped by sunshine, drought and seasonal variation. Its metabolism produces a characteristic mixture of polyphenols. Aspalathin is a particularly distinctive constituent of rooibos. The extensive oxidation involved in producing red rooibos substantially alters this profile of compounds.
At the same time, rooibos has long been consumed as a drink. This raises not only the phytochemical question ‘What does it contain?’, but also ‘What changes during processing and brewing – and what happens after we drink it?’
The central scientific distinction: Identifying a compound in rooibos leaves and demonstrating its antioxidant activity in a laboratory is an important discovery. Whether that translates into a particular effect in humans is a separate research question – not a conclusion that can already be drawn.
We explain how plants use their own antioxidant defence systems, and why wild rooibos populations may differ in their chemical composition, in our article ‘Rooibos – Plant Compounds and Phytochemistry’.
Research & sources
How is rooibos studied – and what can a study really tell us?
The strength of any finding depends first on what was actually investigated. A laboratory measurement answers a different question from an experiment involving intestinal cells or a study in humans.
| Research approach | What is investigated? | What can be concluded? |
|---|---|---|
| Chemical analysis | Aspalathin and other compounds in leaves, infusions or extracts. | Which compounds, and how much of them, are present in the samples tested – not necessarily what they do in the body. |
| Sensory science and food technology | Flavour, colour, oxidation, formulation, moisture or storage. | How specific processing steps affect quality and shelf life. |
| Cell and microorganism experiments | How particular cells, enzymes or bacterial cultures respond to compounds and extracts. | Possible biological mechanisms under laboratory conditions. |
| Animal models | Processes in a living organism under experimentally induced conditions. | Clues about mechanisms that must be investigated separately in humans. |
| Human studies | Measurable changes in volunteers after a defined intake. | Findings for the group and circumstances studied; broader conclusions require sufficiently robust, replicated studies. |
| Systematic reviews | Several published studies assessed against predefined criteria. | How strong the evidence is overall, and where important gaps remain. |
Below, we look at several specific studies – not to turn individual findings into health promises, but to show what questions rooibos researchers ask and what they actually observe.
What do we know about rooibos in humans so far?
Human studies have been conducted, but the evidence is not yet consistent enough to support general health claims. A 2024 systematic review included eight studies involving a total of 175 participants. The measurements included blood and urine markers, along with certain physiological parameters.
Five of the eight studies reported statistically significant findings for at least some of the measures examined. However, the studies used different rooibos preparations, quantities, durations and methods of measurement. The review's authors therefore concluded that the available evidence was not yet sufficient to support reliable general claims about health benefits.
Why this matters: Human research is not starting from scratch: measurable observations already exist. The challenge is to establish which findings can be reproduced in larger, well-designed and comparable studies. Source: systematic review, Beverages (2024).
What did researchers find after people drank green rooibos?
A human study by Breiter and colleagues (2011) explored a particularly practical question: what can be detected in blood and urine after drinking green rooibos?
Twelve healthy men received different preparations of unoxidised rooibos or a comparison preparation in a crossover study. The researchers examined blood and urine samples over a period of up to 24 hours. Among other findings, they detected metabolites of aspalathin and nothofagin in urine; unchanged rooibos flavonoids were detectable in blood only in trace amounts.
A second finding was noteworthy: the ORAC assay used in the study detected no significant increase in the antioxidant capacity of blood plasma. This does not rule out every possible biological interaction. Rather, it shows that a high antioxidant value measured in the original material cannot simply be extrapolated to the human body.
What this study shows: Certain rooibos constituents, or their metabolites, can be detected after consumption. Their detection alone does not establish whether, or in what way, they provide a health benefit.
Source: Breiter et al. (2011), Food Chemistry – bioavailability and antioxidant measurements. We explore the role of infusions, extracts, digestion and absorption in our related article ‘Rooibos and the Food Matrix’.
Why is rooibos being investigated in gut research?
The gut does more than absorb nutrients. Its lining also forms a barrier between the contents of the intestine and the rest of the body. Researchers therefore want to understand whether plant extracts can influence processes at this barrier.
Lesha Pretorius and Carine Smith of Stellenbosch University investigated green rooibos in two zebrafish larval models (published in 2024). In one model, changes to the intestinal lining were induced experimentally; the other examined intestinal motility.
Under the experimental conditions, an aqueous green rooibos extract altered measures of intestinal barrier function, including the junctional proteins ZO-1 and occludin. The extract also reduced certain experimentally induced disturbances in intestinal motility.
The findings raise a research question: can plant compounds interact with biological processes directly at the intestinal surface? This study involved zebrafish larvae, not people drinking rooibos to manage intestinal disorders.
Source: Pretorius & Smith (2024), Journal of Ethnopharmacology.
What role do gut microorganisms play in rooibos research?
Gut microorganisms can transform food constituents and produce metabolites of their own. A research group at Stellenbosch therefore examined how selected microbial cultures respond to green and oxidised rooibos extracts.
Pretorius and colleagues (2022) observed changes in microbial growth and in the release of certain amines in the cultures studied. In particular, measured putrescine production increased, while tryptamine production decreased. Responses varied according to the rooibos preparation.
The interesting finding is the interaction between plant material and microorganisms. However, these were culture experiments outside the human body. The results do not demonstrate a change in the gut microbiota after drinking rooibos, nor do they establish the histamine content of the drink.
Source: Pretorius et al. (2022), Journal of Ethnopharmacology. We explain why histamine in food and histamine produced by the body must be considered separately in ‘Rooibos and Histamine’.
What are researchers studying about aspalathin and mast cells?
Mast cells are part of the immune system. When activated, they can release signalling substances such as histamine. Researchers therefore investigate the signalling pathways through which these cells respond, and whether particular plant compounds can modify those processes in experimental models.
Kim and colleagues studied isolated aspalathin in cell cultures and mouse models of allergic inflammatory responses (published in 2025; first published online in 2024). Under the conditions studied, they observed reduced mast-cell activation and lower histamine release, among other findings.
This is a finding from basic biological research. It does not demonstrate that drinking rooibos tea helps with allergies or histamine intolerance. It does, however, illustrate why an individual rooibos compound may be relevant to research into cellular signalling pathways.
Source: Kim et al. (2025), Inflammation.
Do scientists also study flavour, processing and shelf life?
Yes – food science is an important part of rooibos research. It addresses questions that consumers can readily relate to: why do batches taste different? What roles do heat and moisture play? How can a drink or rooibos powder remain stable during storage?
How can flavour be described scientifically?
Dalene de Beer and colleagues (2024) investigated 57 batches of green rooibos from two processors across five production years. Systematic tastings led to the development of an aroma wheel and a separate wheel describing sensory perceptions while drinking. The researchers identified notes including hay, cooked oats, honey and caramel, as well as an astringent mouthfeel. They also investigated changes during storage.
The wheels provide a vocabulary for differences people can actually perceive. This is research with direct value for quality assessment, producers and tea drinkers alike.
Source: de Beer et al. (2024), Journal of the Science of Food and Agriculture. We explain the wheels in our article ‘Green Rooibos – Aroma, Flavour and Quality’.
Why does packaging matter even for plant compounds?
Another study by de Beer and colleagues (2026) examined rooibos iced-tea powders made from differently formulated extracts under accelerated storage conditions. The researchers compared, among other things, different moisture levels and formulations. At higher moisture levels, aspalathin and colour were less stable; at lower moisture levels, the characteristics examined remained considerably more stable.
This finding has practical implications for manufacturers: it is not enough to establish a high compound content at the outset. Processing, formulation and packaging also help determine how much remains by the time the product is used.
Source: de Beer et al. (2026), Journal of Stored Products Research.
What can we learn from rooibos research as a whole?
Rooibos research has already revealed many connections: specific plant compounds can be identified and measured, processing and storage alter their composition, and a range of biological interactions can be observed in experimental models. Initial studies in humans have also been conducted.
But not every research question can be answered at the same level of evidence. A change measured in intestinal cells, microorganisms or blood is, first and foremost, an experimental observation. Establishing whether it translates into a reproducible health benefit from regularly drinking rooibos requires separate, well-designed human studies.
One open question leads to another: If aspalathin is present in the leaf, how much reaches the cup? How does digestion change it? And which amounts or metabolites become available to the body? These questions are at the heart of our related article ‘Rooibos and the Food Matrix’.
Science is therefore uncovering more than potential biological effects. It also helps explain why rooibos varies with its origin, processing and product form – and how the decisions made by the people behind the product shape those differences.
Selected scientific references
- Systematic review (2024), Beverages – eight human studies with a total of 175 participants, assessing the overall evidence.
- Breiter et al. (2011), Food Chemistry – rooibos flavonoids and their metabolites after consumption by twelve men.
- Pretorius & Smith (2024), Journal of Ethnopharmacology – intestinal barrier function and motility in zebrafish larval models.
- Pretorius et al. (2022), Journal of Ethnopharmacology – rooibos extracts and amine production in selected microbial cultures.
- Kim et al. (2025), Inflammation – isolated aspalathin and mast-cell activation in cell and mouse models.
- de Beer et al. (2024), Journal of the Science of Food and Agriculture – sensory analysis of 57 green rooibos batches and storage studies.
- de Beer et al. (2026), Journal of Stored Products Research – the effects of formulation and moisture on rooibos iced-tea powders during storage.