A Spanish Lab Tests Green Rooibos on Anxious Roundworms and Fish, and the Anxiety Eases

A standardized extract of green, unfermented rooibos eased anxiety-like behavior in zebrafish and roundworms and helped both creatures withstand oxidative stress, researchers in Spain reported this spring. The Ministry files this one carefully, because the cup in your hand and the dish on a lab bench are not the same thing.

The team, led by David G. Valcarce of the Universidad de Leon and the Instituto Espanol de Oceanografia, working with food scientists at ADM's Biopolis unit and the Universitat de Valencia, published the work in the journal BioFactors on May 8. They tested a commercial green rooibos extract, the kind made from leaves that skip the oxidizing "fermentation" step that turns rooibos red, on two small lab animals: the roundworm Caenorhabditis elegans and the zebrafish.

In the roundworms, the extract improved survival under induced oxidative stress and cut levels of reactive oxygen species, the unstable molecules behind that stress, in a dose-dependent way, meaning more extract meant a bigger effect. In the zebrafish, adult fish that had eaten the extract for four months spent more time in the upper part of their tank and less time hugging the bottom in a standard test called the Novel Tank Test, a pattern researchers read as reduced anxiety-like behavior. Their swimming activity itself stayed normal, so the change was read as calmer, not slower.

Both are early, standard tools in this kind of research. Zebrafish and roundworms let scientists test a compound's effects on a whole living animal without the years and expense a mammal study requires, and both are common first steps before anyone designs a trial in mice, let alone people. Nothing here was tested in a human, and the paper makes no claim about what a cup of tea does for a worried mind.

The Ministry's own standing line does not move an inch for this. Rooibos is caffeine-free and rich in antioxidants, among them aspalathin, and that much is settled. What early animal research on green rooibos extract adds is a first data point in a well-worn hypothesis, not a verdict, and the Ministry will report the verdict, if one ever comes, exactly as carefully as it is reporting this.

Sources: Valcarce et al., "Effects of a Commercial Standardized Green Rooibos (Aspalathus linearis) Extract on Caenorhabditis elegans and Zebrafish Anxiety-Like Behavior," BioFactors, vol. 52, issue 3, e70107 (8 May 2026), DOI: 10.1002/biof.70107; Europe PMC record, PMID 42104559.