Rooibos

Generic name: Aspalathus Linearis (Burm. F.) R. Dahlgr.
Brand names: Red Bush Tea, Rooibos Tea, Rooibosch

Usage of Rooibos

Anti-inflammatory effects

Animal and in vitro data

Anti-inflammatory effects of rooibos and of the constituents aspalathin and nothofagin have been studied in models of colitis and vascular inflammation. Suppression of tumor necrosis factor alpha and interleukin has also been demonstrated.(Ajuwon 2013, Kwak 2015, Muller 2012)

Blood taken from 9 atopic adults was used to test the effects of fermented and unfermented rooibos extracts. Both extracts reduced basophil activation in response to allergen exposure, with the fermented extract having a slightly stronger inhibitory effect.(Pedretti 2020)

Bronchodilator and antispasmodic effects have been demonstrated in mice, possibly via potassium channel modulation.(Lee 2015)

Antioxidant effects

Animal and in vitro data

Antioxidant activity has been demonstrated in laboratory experiments and in cellular systems, and has been studied in vivo in rodents and quail.(Ajuwon 2013, Ajuwon 2014, Awoniyi 2012, Ayeleso 2014, Canda 2014, Chen 2013, de Beer 2015, Dludla 2014, Fukasawa 2009, Hong 2014, Joubert 2012, Jurani 2008, McGaw 2007, Pantsi 2011, Simpson 2013) Reported total antioxidant activity varies depending on the assay method and on fermentation and processing methods.(Ulicná 2008) In Wistar rats exposed to nicotine, rooibos demonstrated reduced oxidative stress and vascular injury.(Smit-Van Schalkwyk 2020)

The unique composition of phytochemicals and combination of metabolic activators, adaptogens, and antioxidants make rooibos an attractive yet underappreciated intervention for FB1 toxicoses.(Sheik Abdul 2020) However, despite studies purporting hepatoprotection via antioxidant activity from rooibos tea, one study showed that aspalathin‐rich rooibos extract did not modulate atorvastatin‐induced hepatotoxic effects in a cell model.(Millar 2020)

Clinical data

In a small, acute intervention, crossover study in healthy volunteers (N=15), plasma antioxidant capacity increased significantly with both unfermented and fermented rooibos teas.(Villaño 2010) In another small study among healthy human volunteers, a single serving of rooibos tea did not produce any change in total antioxidant capacity according to the oxygen radical absorbance capacity assay,(McKay 2007) while another study found small increases.(Breiter 2011) Consumption of 6 cups (approximately 1,400 mL) of rooibos tea daily for 6 weeks improved both antioxidant status and lipid profiles among adults with risk markers for cardiovascular disease (N=40).(Marnewick 2011)

Antiviral activity

COVID-19

The clinical features and pathology of acute respiratory disorder induced by SARS-CoV-2 suggest that excessive inflammation, oxidative stress, and dysregulation of the renin angiotensin system are likely contributors to the COVID-19 disease. Rooibos can potentially play a supportive role by modulating the risk of some of the comorbidities associated with COVID-19 in order to promote general health during infections.(Sheik Abdul 2021)

Influenza

In vitro data

An aqueous extract of rooibos was noted to have activity against both influenza A and B, reducing the ability of the virus to adsorb to host cells.(Idriss 2021)

Bone effects

In vitro data

Polyphenols in red and green rooibos increased osteoblast activity and bone mineralization in in vitro studies.(McAlpine 2021) Additionally, in murine macrophages, osteoclast activity was reduced via inhibition of nuclear factor kappa B activity, with fermented rooibos having a slightly greater effect than unfermented.(Moosa 2018)

Cancer

Animal and in vitro data

Suppression of mutagenic activity has been demonstrated in rodents, including studies of liver and skin tumorigenesis,(Marnewick 2005, Marnewick 2011, Marnewick 2009, Ulicná 2008, van der Merwe 2006) with rooibos tea lowering activity to a greater extent than green tea in at least 1 study.(Marnewick 2011) In prostate cancer cells resistant to enzalutamide, treatment with green rooibos extract reduced proliferation and survival via several mechanisms.(Wang 2022) Interference with Akt signaling was determined to be a mechanism of action for a green rooibos extract rich in aspalathin, which inhibited proliferation of prostate cancer cells resistant to castration.(Huang 2019)

Cardiovascular effects

Animal and in data

In hyperlipidemic mice, aqueous rooibos extract reduced serum cholesterol, triglyceride, and free fatty acid concentrations and decreased adipocyte size and number.(Snijman 2007) An in vitro study demonstrated inhibition of adipogenesis following treatment with hot water–soluble solids from fermented rooibos.(Beltran-Debon 2011) Anticoagulant activity has been described for aspalathin and nothofagin in human umbilical endothelial cells and in mice.(Sanderson 2014) These 2 chemical constituents have also shown activity in inhibiting various mechanisms involved in vascular inflammation.(Duke 2002, Ku 2015, Kwak 2015) In mice, hypotensive effects were demonstrated, possibly via potassium channel modulation.(Lee 2015) In rats fed a high-calorie diet, green rooibos extract lowered heart rate and protected heart tissue from ischemic and reperfusion injury. Improvements were also observed for insulin dependence.(Smit 2022) In isolated perfused rat heart, aqueous rooibos extracts showed cardioprotective properties via inhibition of apoptosis.(Pantsi 2011) In a study using human serum, rooibos acted as an angiotensin-converting enzyme (ACE) inhibitor in a manner similar to that of enalaprilat.(Khan 2006)

Clinical data

Following daily consumption of 6 cups (approximately 1,400 mL) of rooibos tea for 6 weeks, improved antioxidant status and lipid profiles (decreased low-density lipoprotein and triacylglycerol, increased high-density lipoprotein) were reported in adults with risk markers for cardiovascular disease (N=40).(Marnewick 2011)

CNS effects

Animal data

Long-term fermented rooibos herbal tea intake affects exploration and anxiety-related behavior in rats, as well as exerts biochemical outcomes in the brain that support the neuroprotective impact of rooibos tea.(Pyrzanowska 2021b)

Diabetes

Animal and in vitro/in vivo data

Experiments in rodents using aspalathin-enriched green rooibos extract,(Mazibuko 2013, Persson 2012) aspalathin,(Han 2014) and enolic phenylpyruvic acid glucoside(Kamakura 2014) suggest that rooibos may have antidiabetic effects, with suppressed increases in fasting blood glucose levels demonstrated. Increased glucose uptake and insulin secretion, as well as reduced insulin resistance, are possible mechanisms of action. Findings were supported by a systematic review and meta-analysis of evidence, in which it was concluded that blood glucose levels were significantly lower in diabetic rodent models treated with a phenolic compound rich in rooibos extracts.(Sasaki 2018)

Another review concluded that rooibos tea has potent antidiabetic properties based on in vitro, in vivo, and various epidemiological studies that suggest consumption of rooibos tea reduces the risk of type 2 diabetes mellitus and its complications. However, the molecular mechanisms of how this herbal tea and its bioactive components impact the major end points of type 2 diabetes mellitus are inconclusive.(Ajuwon 2018) Biotransformation in the gut is most likely responsible for enhancing therapeutic effects observed for the C-glycosyl parent compounds, including aspalathin; these compounds and their derivatives have the potential to regulate multiple factors associated with the development and progression of type 2 diabetes.(Muller 2022)

Clinical data

According to a review, various human studies suggest that consumption of rooibos tea reduces risk of type 2 diabetes mellitus and associated complications.(Ajuwon 2018) In a small, placebo-controlled, crossover study examining effects of several botanical extracts on postprandial glucose levels in prediabetic patients (N=19), clinically significant effects of rooibos were limited to the "less healthy" subgroup of patients. Those whose glucose and insulin parameters were closer to "normal" experienced minimal effects, not statistically different from placebo.(Lim 2021)

Hepatoprotective effects

Animal data

In a rat model of nonalcoholic fatty liver disease, the livers of rats given rooibos tea in addition to a high-fat diet had significantly fewer lesions at study end.(Azubuike 2020)

Metabolic syndrome

According to a systematic review of preclinical studies, rooibos has shown promise in improving metabolic function, in part by reducing markers of oxidative stress and inflammation. Effects were attributed to rutin, a flavonol derivative of quercetin found in several medicinal plants and food sources that have displayed therapeutic benefits against diverse metabolic diseases.(Muvhulawa 2022) Another review highlighted the potential of rooibos extract and aspalathin, a C-glucoside dihydrochalcone, as well as the phenolic precursor Z-2-(beta-D-glucopyranosyloxy)-3-phenylpropenoic acid to prevent metabolic syndrome.(Muller 2018)

In vitro data

Effects of rooibos, aspalathin, and nothofagin on steroid hormone biosynthesis have been investigated in H295R cells.(Baba 2009, Schloms 2012)

Aspalathin inhibited xanthine oxidase activity in vitro and reduced plasma uric acid levels in hyperuricemic mice.(Kondo 2013)

Clinical data

In an analysis of plasma steroid levels in human plasma following rooibos consumption, increased cortisone plasma levels in males and reduced cortisol to cortisone ratios in both males and females were observed.(Schloms 2014)

Rooibos side effects

Information regarding adverse effects is lacking.(Ulicná 2008) Rooibos consumption appears safe in terms of hepatotoxicity; however, there may be a designated group of consumers with higher risk of liver irritation. The contamination of plant material may contribute to herb-induced liver injury.(Pyrzanowska 2021a)

Although microbial contaminants (including Salmonella) may be present due to the fermentation process used to derive the tea product, few reports of contamination exist.(Joubert 2013, Tarirai 2012)

Animal studies have shown increased creatinine levels, but no changes in kidney tissue histology.(Shimamura 2006) A study of human volunteers receiving 6 cups (approximately 1,400 mL) of tea daily for 6 weeks showed increases in serum levels of creatinine, as well as in ALT and AST enzymes.(Marnewick 2011) A case of hepatotoxicity has been reported in a 37-year-old man who consumed 10 cups (2,400 mL) per day of red bush tea for more than a year. He was scheduled for an emergency appendectomy in which his preoperative work-up revealed elevated liver enzymes and thrombocytopenia. All other causes for the hepatotoxicity were ruled out, and the tea was deemed to be the responsible agent.(Reddy 2016)

A risk assessment of the heavy metals in rooibos tea consumed in South Africa concluded that the target risk quotient and the hazard index levels in all analyzed tea samples were well below 1, implying that intake of rooibos tea containing the analyzed heavy metals should not cause a threat to human health. On the other hand, due to high concentrations of trace metals such as chromium, continuous intake may pose a serious chronic health risk due to accumulation in body tissues over time.(Areo 2021)

Before taking Rooibos

Avoid use. Information regarding safety and efficacy in pregnancy and lactation is lacking. Phytoestrogenic effects have been suggested.(Juráni 2008, Opuwari 2015, Shimamura 2006, Stalmach 2009) Rooibos tea has been shown to interfere with steroidogenesis in vivo,(Juráni 2008) possibly due to antioxidant properties, and to improve sperm motility in rats.(Ajuwon 2014, Shimamura 2006) Interference with the acrosome reaction, required for the penetration of sperm to fertilize an egg, has been suggested.(Opuwari 2014) A limited number of in vitro studies suggest an influence of rooibos on basic ovarian cell functions, as well as its potential applicability in female reproductive processes and preventing the effects of environmental contaminants on ovarian functions.(Sirotkin 2021)

How to use Rooibos

Clinical trial data are lacking to support specific dosing recommendations. One small study reported use of 6 cups (approximately 1,400 mL) of rooibos tea per day for 6 weeks to evaluate effects on oxidative stress and biochemical parameters in adults at risk for developing cardiovascular disease.(Marnewick 2011, Schloms 2014)

Warnings

Long-term, high-dose use may impair liver and kidney function, but few case reports exist.(Joubert 2012, Shimamura 2006, Swanepoel 1987, Villaño 2010)

What other drugs will affect Rooibos

No effect on iron absorption has been reported.(Ulicná 2008)

A study on the interaction of rooibos with cimetidine was inconclusive.(Opuwari 2014) Due to the impact on CYP-450, there is a possible risk of herb-drug interactions affecting bioavailability of some coadministered medications. Caution should be exercised.(Pyrzanowska 2021a)

In a study in mice, coadministration of rooibos with atorvastatin resulted in 5.8- and 5.9-fold increases in atorvastatin Cmax and AUC. Altered expression of genes related to metabolism of both cholesterol and fatty acids were also noted.(Patel 2019)

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