Zebrafish Research Reveals Anti-Anxiety Properties of Rooibos Green Tea
Rooibos tea is a uniquely South African product. The plant, Aspalathus linearis, grows primarily in the Cederberg region of the country’s Western Cape Province. And it’s not just a tasty drink. It’s caffeine-free; research has proven that it has anti-inflammatory properties. It has also been found to relieve pain and reduce allergies. Rooibos is also good for heart health.
Like our new study shows, rooibos tea – especially unfermented or green rooibos – can also help reduce anxiety. Our research revealed that this tea extract, prepared with ethanol rather than water, has anxiolytic properties. This means that it prevents or lessens a person’s level of anxiety.
However, we did not come to this conclusion by testing the tea on human subjects. There is huge variation in the severity of anxiety, so a study in humans would require too many participants to give us enough statistical power, and would therefore be too expensive.
Instead, we used zebrafish. Small striped tropical fish may seem like an odd choice, until you realize they are genetically quite similar to humans. For more than 80% of genes known to cause disease in humans, similar genes are represented in zebrafish.
This fact prompted the Faculty of Medicine and Health Sciences at Stellenbosch University to establish the Zebrafish Research Unit just over a year ago. Several studies are underway involving advanced analytical pharmacology, toxicology, identification of therapeutic targets and drug discovery. This study is one of the first to come out of the laboratory.
A variety of data
My research group studies the link between psychological stress and chronic inflammatory diseases. This is particularly important in South Africa: the South African Depression and Anxiety Group estimates that nearly one in six South Africans suffers from anxiety or depression. Moreover, the current 10 leading causes of death in South Africa, such as tuberculosis, diabetes and respiratory diseases, all have inflammation as a common feature.
Zebrafish is ideal for drug discovery, especially in the context of neurological and inflammatory diseases. We are able to perform extensive testing, including not only behavioral assessment and seeing how specific treatments work, but also assessing the risks of overdose and long-term use of potential treatments.
So we decided to use our zebrafish models to see if rooibos could have positive effects on anxiety. Most of our research is done in the early larval stage, when zebrafish are not yet considered a susceptible animal. It’s a more ethical way to use a living organism in research, because they can’t feel pain at this stage.
We immersed the 2 mm long zebrafish larvae in different concentrations of rooibos in a small dish. Basically, they were swimming in tea; this is absorbed through their skin as well as their gills, as their mouths are not yet open.
Read more: Pasha 127: Allergies vs rooibos: can this South African plant help sufferers?
At different times, specialized equipment tracked their movement and this was used to build behavior patterns. Using an anxiety model – which involves exposing larvae to alternating bright light and darkness for short periods – we assessed whether larvae swimming in rooibos were able to remain calm, comparing their behavior to that of non-supplemented larvae. Normally, in this model, the larvae “freeze” in bright light, followed by hyperactivity during periods of darkness. In our study, rooibos-treated larvae also froze, but did not show anxious hyperactivity.
We also performed a test using the behavior of live larvae to probe a specific mechanism: a “feel good” neurotransmitter, GABA, whose signaling can be manipulated by enhancing or blocking its receptor. If the receptor is blocked, the larvae exhibit a seizure-like hyperactive behavior. In our study, rooibos was able to completely prevent this response – in fact, it showed similar results to an anti-epileptic drug known to act via GABA.
Behavioral testing was supplemented by whole-body analyzes for oxidative stress and antioxidant activity, as well as cell culture work using human cells. In these models, we showed that green rooibos was able to protect human neurons against oxidative stress.
Oxidative stress increases throughout life and is actually responsible for aging, so a product that can protect the brain from oxidative stress can essentially slow down our aging process. In a world where advances in medicine allow us to age, it is becoming increasingly important to be able to prevent the brain from aging.
Together, our data suggest that rooibos green tea could be considered a functional food for the brain. Research suggests it could be a good option as a starting ingredient in the development of new nutraceuticals – pharmaceutical alternatives that claim physiological benefits.
The results of this study mean that we could have discovered the contribution of nature to the treatment of certain health problems in South Africa. It shows that drinking rooibos green tea can have a calming effect if you suffer from anxiety.
Zebrafish in research
This certainly won’t be the last research from our lab or others using zebrafish in drug discovery. The fish, native to Malaysia, could be the new rodent in research. Besides their genetic similarities to humans, when in the larval stage, the fish are quite transparent; making them ideal for microscopy.
Read more: How zebrafish got their stripes
We have a few tanks where we breed with adult stock. The fish can live up to three years in the lab, compared to about a year in the wild (due to excellent care in the lab, but also the lack of natural predators).
In terms of future research, evaluating these effects in humans is on the cards. We are also generating very promising results on rooibos in the context of inflammatory bowel syndrome, a chronic disease affecting approximately 10% of the world’s population and which is the most common comorbidity of anxiety disorders.