Aspalathus linearis (of the family Fabaceae), better known as Rooibos or Red Bush Tea, is a plant which is used to make a mildly sweet and astringent tea as well as a recent flavoring agent which serve as a commodity from African nations in which it is grown. This species is almost exclusively known as Rooibos (sometimes aspalanthus pendula is used due to similar taste properties)
The comparatively low caffeine and tannin content (both bitter compounds) makes the tea more palatable while the antioxidant content makes it a highly marketable herb. Due to the high rate of usage in recent decades, it appears to be on track to become the second most world-wide consumed tea beverage (second to camellia sinsensis, the main source of green tea catechins).
Rooibos is a plant (Aspalathus linearis) that is frequently brewed as a tea. Coming from African countries, Rooibos appears to be increasing in popularity due to its more palatable taste (less bitterness and mild sweetness when compared to green tea) and antioxidant content
Aspalathin (dihydrochalcone glycoside, of which the closest flavonoid structure would be phloretin) at 9.68+/-1.78% of unfermented leaves and 0.10+/-0.03% of fermented leaves and the cyclic version Aspalalinin; it has been said that the overall range of aspalathin in unfermented Rooibos is 4-12%, and while aspalathin alone is 84.5% of total flavonoids in unfermented tea it drops to 22.4% after fermentation
Nothofagin (dihydrochalcone glycoside) at 0.97+/-0.28% of unfermented leaves and 0.010% in fermented leaves
The flavonoid glycosides Orientin (Eriodictyol-8-C-glucoside) at 0.83+/-0.17% (unfermented leaves) and 0.22+/-0.02% (fermented) as well as the isomer Isoorientin (Eriodictyol-6-C-glucoside) at 1.52+/-0.33% (unfermented) and 0.34+/-0.02% (fermented); eriodictyol is structurally similar to luteolin
Z-2-(β-d-glucopyranosyloxy)-3-phenylpropenoic acid (PPAG) at 0.14+/-0.20% of unfermented leaves and 0.07+/-0.02% of fermented tea, although some sources suggest no real difference; can reach up to 1% of high PPAG tea leaves
Procyanidins including bis-fisetinidol-(4β,6:4β,8)-catechin (trimer), an undisclosed pentamer, and procyanidin B3
Vladinol F and Vanylglycol
Vicenin-2 (isoflavone glycoside)
Carlinoside, neocarlinoside, and isocarlinoside (diglycosides of eriodictyol
The lignan Secoisolariciresinol
Hydroxycinnamic acids such as ferulic acid, caffeic acid, and 4-coumaric acid
Chlorophyll (usually extracted from the tea)
A small sparteine content
Beyond the aforementioned phytonutrients, Rooibos has a polysaccharide that consists of 63.8% glucose, 10.2% galactose, 16.3% mannose, and 10.6% Xylose; this polysaccharide is not found in hot water extracts like tea.
The main bioactive is aspalathin and the two structurally related chalcones (nothofagin and aspalalinin), and most other bioactives are flavonoids based off of either eriodictyol or luteolin. Aspalathin is by far the most prominent bioactive and is subject to degradation by fermentation
When measuring commercial based tea products, the bioactives seem to be somewhat variable; the highest estimates being up to 0.43+/-0.24% (aspalathin), 1.38+/-0.19% (orientin), and 0.93+/-0.17% (isoorientin) but with many products not having a detectable content. The content of aspalathin is significantly lower than the estimates in non-fermented leaves (9.68+/-1.78%) which is due to the processing of true Rooibos tea requiring fermentation.
Despite being known as having a 'comparably low tannin content' up to 50% of the water extract of Rooibos is tannin-like compounds which are mostly unidentified; still less than plants from camellia sinensis (black, white, and green tea) where tannins contribute to the bitterness of the tea.
Rooibos has a comparable low (but still present) tannin content and a present polyphenolic content; tea products on the market seem to have a fair bit of variability due to differences in sources and processing
Pure aspalathin is highly water soluble (octanol/water partition coefficient (Poct) of −0.347) and appears to be tasteless although fractions containing aspalathin have shown differential taste properties (a bitter taste, as well as a weak sweetish taste). It was thought initially that coelution of Z-2-(β-d-glucopyranosyloxy)-3-phenylpropenoic acid (PPAG) with aspalathin could explain the sweetness, but isolated PPAG appears to have a slightly bitter and astringent taste.
Any molecule with a β-d-Glucopyranoside structure, which includes PPAG, retains the potential to active the human bitter receptor known as hTAS2R16.
The compounds that have been tested for their sensory properties have been noted to be mildly bitter
Rooibos tea can be bought in either a fermented or an unfermented form, the difference being that the former (fermented) allows the characteristic red-brown color and sweetish flavor to be brought out. This fermentation process is known to reduce the content of aspalathin and nothofagin significantly.
Fermentation makes Rooibos tea more palatable, but at the cost of the main bioactive (aspalathin) undergoing oxidative metabolism
While 60 seconds of steam pasteurisation is sufficient to reduce the aspalathin content of rooibos, 120 seconds can reduce levels of all measured bioactives and it is thought the higher sensitivity of aspalathin to heat losses is due to converion into other flavonoids (although this was not demonstrated during processing). Losses can reach up to 78.5%, although are usually lower and losses of orientin based flavonoids tend to be less than 10%.
Elsewhere, temperatures of 121°C (normal temperature sterilization) or 135°C (high temperature) for 15 and 4 minutes, respectively, has reduced flavonoid content. 91°C (standard pasteurisation) for 30 minutes did not reduce the content, and adding in either citric acid or vitamin c to the processing preserved aspalathin content. Other processing steps including extraction, microfiltration, reverse osmosis, and concentration do not modify aspalathin content.
Stability of the major bioactive, aspalathin, appears somewhat sensitive to heat treatment at higher temperatures as well as to fermentation; other processes, such as filtration or concentration, do not damage the aspalathin content
When oxidized, aspalathin is thought to be converted into dihydroorientin and dihydroisoorientin (via enclosing the dihydrochalcone structure into a flavonoid structure) which can then produce orientin and isoorientin; which was then confirmed in vitro at pH 7.4 and a temperature of 37°C. Specifically, it seems that aspalathin oxidizes into two isomers of dihydroisoorientin (R and S isomers eriodictyol-6-C-glucoside) which then directly oxidize to isoorientin, while aspalathin oxidation into dihydroorientin (R and S isomers of eriodictyol-8-C-glucoside) causes production of isoorientin (irreversible) which then may produce orientin.
Another possible oxidation product of aspalathin is a dimer, which forms after initial oxidation of aspalathin.
Aspalathin can be readily oxidized ex vivo (prior to consumption and during processing) to form isoorientin, which then may produce orientin; a possible dimer (pairing) of aspalathin molecules may also occur
Green Rooibos Tea is marketed as a healthier version of Rooibos due to a higher aspalathin content, as it is an indication of fermentation. During the fermentation process, Rooibos tea turns from a natural green pigmentation to the characteristic red pigemntation.
This has been quantified at 287mg (636μM) per 500mL brewed tea and a higher nothofagin content (34.4mg/79μM) as well as both orientin (26mg/58μM) and isoorientin (17mg/38μM) have been quantified.
Green Rooibos tea is unfermented Rooibos tea, and it appears to have a higher aspalathin content than does regular (fermented) Rooibos tea
There is a combination formula known as CRS-10 that involves a combination of the water extract of Rooibos and the water extract of Dandelion.
In an in vitro analysis of aspalathin transportation across the intestinal wall occurs in a time and concentration dependent manner with concentrations of up to 1-2mg/mL reaching 80-100% absorption, experiencing a plateau after 60 minutes.
When looking at in vitro analyses, it appears that the dihydrochalcone glycosides (aspalathin mostly) are actually well absorbed past the intestinal wall
In pigs, ingestion of aspalathin has resulted in urinary levels of aspalathin itself despite being a glycoside (albeit less than 1% of the oral dose) which has also been confirmed in human volunteers.
This is similar in humans given Rooibos tea containing 90+/-4.4μM (41+/-2mg) aspalathin per 500mL and 159μM total flavonoids, a total of 352nM of flavonoids were excreted in urine (0.22% of oral dose) and when drinking fermented tea (84μM total flavonoids) a total of 0.09% of the flavonoids were detected in urine. This has been noted elsewhere, where in humans given Rooibos tea where the peak serum concentration of total flavonoids was 0.76nM and overall absorption was determined to be 0.26%.
Despite the good intestinal transit in vitro, the bioactives of Rooibos have a very poor absorption rate and bioavailbility of less than half of a percent
In vitro, it appears that less than 0.1% of the applied dose of aspalathin is transportered across various skin cell cultures (whole skin, dermis and epidermis, statum corneum) and that there are no differences between isolated aspalathin and Rooibas extract.
Aspalathin (in pigs) has been noted to be methylated, glucuronidated, both, and also excreted in either its unchanged state or as an aglycone. This is similar in humans, most of which (over 50%) was the O-methylated form of the glycoside.
Despite being a dihydrochalcone glycoside, aspalathin is still further metabolized and its methylated form is the primary human urinary metabolite
157-167mg/kg aspalathin (via unfermented rooibos ingestion) daily for 11 days in pigs has resulted in less than 1% of the ingested dose being excreted in urine. Upon cessation of supplementation, no detectable urinary metabolites are seen after 36-48 hours.
In vitro, Rooibos water extracts appear to have CYP3A inhibitory potential yet ingestion of Rooibos tea (4g per liter of water, boiled for five minutes and ingested daily for two weeks) was shown to reduce the AUC of midazolam in plasma was reduced 70%. When looking at CYP3A after oral ingestion of the tea, total CYP content was unchanged (while there was a trend to increase CYP3A) while the hydrolyxation capacity of CYP3A was increased nonsignificantly by 40%.
Chronic ingestion of Rooibos appears to increase the activity of CYP3A4
At least one study in C.Elegans being fed Rooibos extract noted an increased lifespan that was longer with unfermented 'green' Rooibos than with fermented Rooibos, implicating aspalathin and antioxidative properties. In a model of glucose-induced oxidative stress, Rooibos was able to increase lifespan by 14% (fermented) and 22.5% (unfermented) although Rooibos failed to increase lifespan when C.Elegans were not subject to oxidative stress.
The antioxidant properties are generally doing antioxidant things, although Rooibos does not appear to have an inhernet longevity promoting effect
Seven weeks of ingestion of Rooibos tea at 2% of the drinking water (2g per 100mL) prior to ischemia/reperfusion appeared to exert some cardioprotective effects as assessed by aortic output recovery; this was associated with a preservation in cardiac GSH levels.
In humans, heart rate does not appear to be altered with ingestion of 400mL Rooibos tea.
Angiotension-converting enzyme (ACE) is a zinc carboxypeptidase that is synthesized by and present on the endothelium that, when in high activity, causes cell growth and vasocontriction. Its inhibition is a pharmacological target for reducing blood pressure, and Rooibos has been investigated for its role.
Rooibos extract is an ACE inhibitor with Vmax of 6.76µM and KM of 0.78µM, and is classified as a mixed type inhibitor. It appears that oral ingestion of 400mL Rooibos tea causes a statistically significant reduction in ACE activity, suggesting it is an ACE inhibitor; the degree of this reduction was practically very small and failed to result in any alterations to blood pressure.
Rooibos appears to be an ACE inhibitor, but the degree which it works in a human following tea ingestion appears to be very small and is not associated with reductions in blood pressure
Nitric oxide concentrations do not appear to be altered with ingestion of Rooibos tea.
Nitric oxide, which reduces blood pressure, is not influenced with oral ingestion of Rooibos tea
In mice that lack the LDL receptor and are fed a high fat diet (highly susceptable to diet induced obesity) Rooibos appears to exert hypolipidemic effects in a manner that does not affect normal mice.
In persons at risk for cardiovascular disease who consume six cups of Rooibos tea daily for six weeks, there are significant reductions in LDL-C (15%) and triglycerides (29.5%) as well as a significant increase in HDL-C (33%) relative to themselves during control.
May beneficially influence lipoproteins and triglycerides, but this seems to be an acute effect rather than curative based on preliminary evidence
α-glucosidase appears to be inhibited in vitro with a 18% aspalathin extract of Rooibos with an IC50 of 2.2μg/mL.
In response to a 2g/kg oral glucose tolerance test, 30mg/kg of an extract of Rooibos with 18% aspalathin appears to reduce blood glucose acutely in rats at one hour (27.3%), two (33.7%), and four hours (58%) post ingestion with a potency exceeding that of 10mg/kg vildagliptin. Isolated aspalathin at 1.44mg/kg (equivalent to 8mg/kg of the aforementioned extract) was effective in isolation by reducing blood glucose by 11.6+/-3.4%.
At least one study has noted weight gain suppression in mice fed a chow diet (high carbohydrate) but not a high fat diet which was not associated with a reduction in food intake.
Rooibos appears to have an ability to inhibit some carbohydrate uptake following oral ingestion, which would be a health mechanisms that circumvents its poor absorption rates. The hypoglycemic effect in response to an oral glucose tolernace test seems quite respectable but lacks human data
In isolated liver cells (chang cells), the bioactive PPAG appears to enhance glucose uptake with an EC50 of 3.6μM and activity as low as 1μM while 0.05–5μg/mL of an 18% aspalathin extract concentration-dependently increased glucose uptake; aspalathin and rutin were both ineffective in isolation. This may be related to an activation of AMPK seen with Rooibos extract which occurs in liver cells but not adipose (seen at 600μg/mL).
In vitro, PPAG from Rooibos appears to increase glucose uptake into cells which may be related (but is not confirmed to be related) to AMPK activation
In diabetic rats given rooibos tea at an equivalent of 300mg/kg of plant extract for eight weeks, rooibos failed to reduce blood glucose concentrations whereas elsewhere aspalathin at 0.1-0.2% of the diet to mice prior to diabetes induction over five weeks appears to attenuate the increase in blood glucose with an efficacy comparable to the reference drug of 0.005% pioglitazone.
Differing results in animal models
One human study in persons at risk for cardiovascular disease noted that blood glucose was nonsignificantly reduced by 14.4% over six weeks of consuming six cups of unfermented Rooibos daily.
Oddly, a human study in otherwise healthy persons given Rooibos tea at 750mg (tea leaf weight) noted an increase in blood glucose reaching 21.6% (unfermented) and 32% (fermented); this spike occurred at 30 minutes and was wholly normalized within an hour.
Possible reductions in blood glucose seen in humans, although they have failed to reach statistical significance
Aspalathin appears to stimulate insulin secretion from isolated RIN-5F cells at 100μM but not 10μM, a concentration that may be too high to be relevant to oral ingestion.
The stimulation of insulin seen with Rooibos occurs at a very high concentration and is likely not relevant to oral supplementation or tea consumption
The possible oxidative stress of AGEs upon pancreatic cells (RIN-5F cell line) appears to be attenuated with incubation with aspalathin (concentration dependent between 25-100μM).
In diabetic rats given rooibos tea at 5mL/kg (or 300mg/kg dry weight of the plant) for eight weeks, supplementation failed to reduce fructosamine and HbA1c (as well as blood glucose) yet reduced advanced glycemic end product (AGE) formation; the control group, 150mg/kg N-acetylcysteine, failed to have any effect.
General antioxidative effects may reduce some glycation products
In vitro, aspalathin at 1-100μM causes concentration dependent increases in muscle cell (L6 Myocyte) glucose uptake in the absence of insulin, with no significant differences between 10μM and 100μM to a near doubling and this being replicated in C2C12 myotubes. When looking at an extract containing 18% aspalathin, 0.05–5μg/mL was able to concentration dependently increased glucose uptake with a potency statistically comparable to insulin and metformin (1μM).
Aspalathin itself has been confirmed to actiate AMPK in skeletal muscle tissue (in vitro with L6 myocytes in a concentration dependent manner up to 100μM) and it has been noted that both the fermented and unfermented extracts (10μg/mL) are of similar efficacy.
Rooibos appears to stimulate glucose uptake in muscle cells both in the presence and absence of insulin, thought to be related to AMPK activation
Palmitate induced insulin resistance in myocytes (exposure to palmitate causing accumulation of some intermediates such as DAG and ceramide, which impair glucose uptake by interfering with IRS-1) appears to be circumvented with Rooibos whether in the presence of insulin or not, with the unfermented extract having more potency than the fermented. This study noted that metformin (an AMPK activator) having no effect, and it appeared that Rooibos worked via downregulating PKC theta (PKCθ) which is an intermediate between DAG/ceramide and their inhibitory effect on IRS-1.
Appears to reduce insulin resistance at the level of the muscle cell, and this appears to be from dysregulating the negative effects of excess fatty acids and their insulin resistance inducing metabolites; the fatty acid metabolites (DAG and Ceramide) normally suppress IRS-1 (needed for proper insulin signalling) via increasing PKCθ, and Rooibos appears to reduce PKCθ
In collegiate wrestlers who lost 3% of their body weight during a training session (water weight), ingestion of Rooibos tea does not appear to be more effective than water when looking at rehydration in athletes.
In vitro, extracts of Rooibos appear to be relatively potent antioxidant which is known to correlate with the aspalathin content; suggesting that unfermented or 'green' Rooibos products are more antioxidative than fermented leaves. When compared to other tea products, it appears that unfermented Rooibos (the more potent variant) is less potent as assessed by total radical-trapping antioxidant potential (TRAP) than lemon juice and two variants of the plant camellia sinensis (black and green tea).
It appears to be an antioxidant in vitro, but its potency is less than that of green tea
In rats, oral ingestion of 2% camellia sinensis or Rooibos tea (2g leaf extract per 100mL of drinking water) noted that the plant bearing green tea catechins was significantly more effective than the same dose of Rooibos in increasing plasma antioxidative capacity. Green tea was approximately three-fold more potent than both fermented and unfermented versions of Rooibos even when less was ingested (due to less water consumption).
In comparative studies, Rooibos appears to be significantly less antioxidative than green tea even when green tea is consumed at a lower dose
Following ingestion of Rooibos tea in humans (500mL of green Rooibos tea with 287+/-0.1mg (636μM) aspalathin), there were no significant alterations in total plasma antioxidant capacity (ORAC) which was attributed to its poor absorption rate. Elsewhere, in healthy humans given 500mL of a tea made from 750mg tea leaves (aspalathin content not given) there was an acute increase in antioxidant potential in the blood by 6.6% (unfermented) and 2.9% (fermented) which peaked within an hour and lasted for five hours.
A later intervention where six cups of unfermented Rooibos was ingested daily over the course of six weeks in persons with increased cardiovascular disease risk caused also failed to note changes in ORAC yet noted reductions in lipid peroxidation (TBARS) by 54% and a beneficial change in glutathione redox status, suggesting some antioxidative effect.
Human studies assessing the antioxidative potential of Rooibos have failed to find changes in plasma antioxidant capacity even with very high aspalathin doses, although levels of lipid peroxidation have been noted to be decreased in one study fairly potently
Incubation of Rooibos extract (7.8125-250µg/mL) to unstimulated whole blood cultures (containing immune cells) appears to cause increases in levels of IL-6, IL-10, and IFN-γ whereas when the whole blood culture is stimulated the increase in IL-6 persists while IL-10 is reduced and IFN-γ unaffected. This induction of IL-10 has also been shown in splenocytes at 10-1,000µg/mL.
Rooibos has been noted to increase antigen-specific antibody production in vitro and oral ingestion of Rooibos can restore a cyclosporin A induced reduction in antigen production; this was thought to be due to a polysaccharide or oligosaccharde and not a flavonoid.
Nonspecific antibody response (via LPS stimulation of B-cells) was not affected at any concentration between 10-1,000µg/mL.
There may be an increase in antigen-specific antibodies, but not general nonspecific antibody production, seen with Rooibos tea
In HIV infected patients subject to a survery about alternative medicine (in South Africa), there appeared to be limited usage of alternative medicine yet of those reporting usage Rooibos tea appeared to be frequent.
An alkaline fraction appears to prevent HIV associated cytopathicity with an EC50 of 38.9µg/mL, which was improved to 8µg/mL with an ethanolic extraction and the polysaccharide purified from this fraction (63.8% glucose, 10.2% galactose, 16.3% mannose, 10.6% Xylose) at 250µg/mL almost fully blocked HIV replication; a hot water extract failed to show anti-HIV properties, showing the water insolubility of this polysaccharide.
Preliminary evidence suggests a possible anti-HIV property of the polysaccharides in this tea
When assessing possible estrogenic compounds in Rooibos, three compound showed estrogenic activity (assessed by their relative potency to estradiol); nothofagin (100µg nothofagin being as potent as 2.157µg/L estradiol), isovitexin (1.572µg/L), and luteolin-7-glucoside (1.637µg/L). All phytoestrogens were less potent than genistein (from soy isoflavones) and resveratrol as reference compounds.
The phytoestrogens of Rooibos appear to be very mild and probably not relevant to oral supplementation of the tea
Men given 200-400mg of a combination supplement known as CRS-10 (Dandelion and Rooibos water extracts; ratio not given) over four weeks reported that the men given the higher dose had a significantly improved quality of life. The authors suggested that this was due to testosterone, as in elderly male rats there was a 43% increase associated with improvements in testicular function and survival.
The potassium channel opening properties of Chrysoeriol (a flavonoid found in this tea) appears to cause bronchiodilation; it is incertain how this applies to Rooibos tea ingestion due to a low chrysoeriol content.
The increase in liver enzymes seen in diabetic rats is slightly attenuated with oral ingestion of rooibos tea (5mL/kg of the tea or 300mg/kg of the extract) with a potency comparable to 150mg/kg N-acetylcysteine; this was attributed to antioxidant effects. Rooibos was slightly more effective at decreasing lipid peroxidation in the liver relative to N-Acetylcysteine, but comparable in serum and other organs (lens and kidneys) and this hepatoprotective effect has been seen with 7g/kg Rooibos (dry leaf weight after brewed into a tea) against tert-Butyl Hydroperoxide induced hepatoxocity.
General antioxidative properties may exert some protection against oxidative stressors, although the oral doses of Rooibos used are quite high
In rats who were given free access to drinking water that was spiked with 2g Rooibos per 100mL, after 10 weeks there were no significant changes in testicular weight although a small increase in seminal motility was noted with both fermented and unfermented Rooibos. Elsewhere, this same dose (2%) Rooibos and a higher dose (5%) over 52 days noted beneficial effects on spermatids (count, motility, and viability) although fermented tea (not unfermented) was associated with an increase in spontaneous acrosome reactions.
For the most part, Rooibos seems to benefit seminal function of the rat. There is one atypical event (spontaneous acrosome reactions) which is not typically seen as beneficial and needs further research
When looking at the catalytic activities of CYP17A1 and CYP21 (both convert pregnenolone into 17-hydroxypregnenolone, although the former is involved in androgen synthesis and the latter corticosteroid synthesis) in isolated COS-1 cells, it appears that aspalathin and nothofagin at 10μM are able to inhibit conversion of pregnenoline into 17-hydroxypregnenolone via CYP17A1 by 39% and 29%, respectively, with inhibitory potential against CYP21 by aspalathin (32%) and nothofagin (41%).
In H295R cells, both aspalathin and nothofagin fail to alter steroid synthesis significantly under basal conditions (except for a small increase in aldosterone) whereas when stimulated by forskolin both dihydrochalcones as well as Rooibos extract itself (1mg/mL) were able to suppress androgen and cortisol synthesis.
May have inhibitory effects on steroid synthesis in the adrenal glands; practical relevance of this information uncertain (due to high concentrations required)
It appears that a water extract of Rooibos tea (0.3-10mg/mL) may cause intestinal relaxation in instances of low potassium concentrations but not high. As this was similar to the potassium channel opener Cromakalim, it was said that Rooibos opened potassium channels which was confirmed with the bioactives Chrysoeriol, Orientin and Vitexin. This relaxation with Rooibos has been replicated elsewhere.
Appears to have some minor antispasmodic properties due to being a potassium channel opener
In a rat model of colitis (inflammatory bowel disease), Rooibos tea ingestion appears to beneficially influence markers of oxidation (superoxide dismutase) and DNA damage (urinary 8-hydroxy-2'-deoxyguanosine) relative to control.
One case study exists where a women diagnosed with low-grade B-cell malignancy six years prior to the event (and currently in a stable state) on rituximab and prednisone noted highly elevated liver enzymes with no apparent clinical toxicity symptoms, and this was associated with consumption of Rooibos tea at around one liter daily (teaspoon of leaves per serving, assumed 150mL). While cessation of tea normalized liver enzymes, the product was not named (and contamination not ruled out) nor was a reintroduction for causation conducted.