The Journal of the American Botanical Council
Issue: Page: 34-
by Laurie Erickson
Antioxidants are hot topics in the health news these days, and an herbal tea called
rooibos (pronounced ROY-
A Note on Tea Terminology
In the strict sense, the word tea has been reserved for infusions made from leaves
of the evergreen shrub Camellia sinensis (L.) Kuntze, Theaceae, while infusions made
from herbs such as rooibos have been called tisanes. Over time, however, the common
use of the word tea has been extended to include herbal infusions, and this relaxed
usage is followed here. Rooibos is often referred to as red tea because it makes
a vibrant red-
Rooibos is a shrubby legume that is indigenous to the mountains of South Africa’s
The type of A. linearis that is cultivated commercially for tea is the Red type,
also known as the Rocklands type;1,6 it is native to the Pakhuis Pass area in the
northern Cedarberg region.6 The Rocklands type grows erect, up to 1.5 m (about 5
feet) in height. It has a single basal stem that divides just above the ground surface
into multiple thin branches that carry bright green, needle-
Rooibos has adapted to coarse, nutrient-
One study found genetic variations between four morphologically different populations of A. linearis.1 The authors suggest that the wild forms of A. linearis might be used to improve characteristics, such as yield and disease resistance, of the cultivated form. They also observe that because the cultivated Rocklands form is being grown outside of its original Pakhuis Pass location, this introduction of the cultivated form into new areas could threaten the genetic integrity of the wild forms in these areas.
A later study7 showed genetic differences between populations of A. linearis that are sprouters (plants that can resprout from a deep rootstock to regenerate after a fire) and populations that are seeders (plants that rely on producing plentiful seeds to reproduce). The authors suggest that reseeding is the primitive character state in A. linearis and resprouting is a derived state that evolved to help the plant survive in a region prone to wildfires. The rooibos plant that is commercially grown for tea is the seeder type.7
In addition to differences in morphology and genetics, researchers have found differences in chemistry between various populations of A. linearis.6,9 Van Wyk, of the Department of Botany at Rand Afrikaans University, presented results of his tests on the different wild populations of rooibos, showing significant variations in the polyphenol profile by population.9
inhabitants of the mountainous regions of South Africa’s Western Cape were the first
to collect wild rooibos and use it to make tea.10 These people discovered that they
could brew a sweet, tasty tea from rooibos leaves and stems that they cut, bruised
with wooden hammers, fermented in heaps, and then sun-
Rooibos became a cultivated crop by the early 1930s, has been grown commercially since World War II, and now is exported to countries worldwide, including Germany, Japan, the Netherlands, England, Malaysia, South Korea, Poland, China, and the United States.10 In 1999, about 29 percent of South Africa’s total rooibos sales were exported to 31 countries.10 The quantity of rooibos exported in 2000 was two and a half times greater than the quantity exported in 1999, and exports continue to grow.10 The small towns of Clanwilliam and Wupperthal, north of Cape Town in the Cedarberg region, have a long history of rooibos cultivation; these towns are popular tourist stops because of their beautiful rural scenery and their role in the rooibos industry.
Roughly 70 percent of the bulk rooibos that is exported goes through Clanwilliam-
Rutgers University provides a quality control program for ASNAPP’s Wupperthal tea program, evaluating parameters such as color, taste, aroma, pH, moisture content, cleanliness, total phenol content, and antioxidant capability for tea samples collected from the industry in general and from all the growers in the Wupperthal tea program.11 Data from their analyses are made available to the farmers and also to prospective buyers via product specification sheets.
The Perishable Products Export Control Board (PPECB) of South Africa ensures that all exported rooibos products pass a phytosanitary inspection and are certified to be free of bacteria and impurities.4,10 In order to pass these health and safety tests, rooibos producers steam pasteurize the tea as the final step before packing. Organic rooibos is also monitored by various international organizations that provide organic certification, such as the German firms Ecocert and Lacon.
Harvesting and Processing: Fermented and Unfermented Rooibos
When rooibos is cultivated commercially, the needle-
Antioxidants in Rooibos
Free radicals (unstable molecules that have lost an electron) can damage the DNA in cells, leading to cancer, and they can oxidize cholesterol, leading to clogged blood vessels, heart attack, and stroke. Antioxidants can bind to free radicals before the free radicals cause harm. Some antioxidants are called polyphenols because these substances contain a phenolic ring in their chemical structure. Polyphenols are common in plants; they act as pigments and sunscreens, as insect attractants and repellants, and as antimicrobials and antioxidants.12,13 The polyphenol group is further divided into subgroups such as flavonoids and phenolic acids. Polyphenols can also be classified as monomeric (molecules containing a single unit) or polymeric (larger molecules containing more than one unit). As described in this section, laboratory studies have found that rooibos tea contains polyphenol antioxidants, including flavonoids and phenolic acids, that are potent free radical scavengers.
Flavonoids: The polyphenol antioxidants identified in rooibos tea include the monomeric
flavonoids aspalathin, nothofagin, quercetin, rutin, isoquercitrin, orientin, isoorientin,
luteolin, vitexin, isovitexin, and chrysoeriol.14-
A recent analysis of fermented rooibos measured the levels of all the flavonoids listed above except nothofagin (see Table 1).19 Of the 10 flavonoids measured, the three that occurred in largest amounts were aspalathin, rutin, and orientin, followed by isoorientin and isoquercitrin. Nothofagin was identified by mass spectrometry but was not quantified because a standard was not available. The amount of nothofagin in fermented and unfermented rooibos was estimated to be about three times less than aspalathin in one study.20 Aspalathin and nothofagin arepresent in relatively large amounts in unfermented rooibos tea,19,20 but some of the aspalathin and nothofagin oxidizes to other substancesduring fermentation; thus, fermented rooibos contains less aspalathin and nothofagin than unfermented rooibos.20 The change in polyphenol composition is the reason the tea changes color with fermentation.20
Phenolic Acids: In addition to flavonoid antioxidants, rooibos also contains phenolic
acids that have been shown to have antioxidant activity.14,18,21 Like flavonoids,
phenolic acids are polyphenol substances that are found in fruits, vegetables, and
whole grains. The phenolic acids identified in rooibos tea, in decreasing order of
antioxidant activity as measured in one study21 with the commonly used 1,1-
Total Polyphenol Content: Despite some promotional claims, a serving of rooibos tea
has less total polyphenols than the same size serving of green or black tea. Serving
size varies, but for comparison purposes a 150 to 200 ml serving is often used (about
3/4 of a standard baking measuring cup). Elizabeth Joubert, Ph.D., specialist researcher
at South Africa’s ARC Infruitec-
Quercetin and Luteolin: Two of the flavonoids in rooibos tea, quercetin and luteolin,
are potent antioxidants found in many fruits and vegetables. Studies in vitro (in
the test tube) have shown that these antioxidants can cause cancer cells to "commit
suicide," referred to as apoptosis.24-
Although studies like these show quercetin and luteolin are strong antioxidants, researchers haven’t yet determined whether enough of either of these two flavonoids are present in rooibos tea and absorbed by the body to have beneficial effects. As shown in Table 1, recent analysis of fermented rooibos found considerably more quercetin than luteolin,19 but even quercetin was present in much lower amounts than aspalathin, orientin, and rutin.
Based on the data in Table 1, a 150 ml serving of fermented rooibos tea made with 2.5 g of tea leaves has about 0.27 mg of quercetin; for comparison, one study found that C. sinensis contains 1.5 to 3.75 mg of quercetin per 150 ml serving of tea.35 A previous study36 found 1.5 mg of quercetin per 150 ml serving of fermented rooibos, but that may be an upper limit. Joubert says that the 1.5 mg estimate is probably high,22 but emphasizes that these estimates will vary with parameters such as the brewing time and the amount of water and tea leaves used. At any rate, the amount of quercetin per serving of rooibos is a small percentage of the total polyphenol content per serving of rooibos.
Aspalathin and Nothofagin: A unique polyphenol that is one of the most abundant monomeric flavonoids in rooibos tea,19,20 aspalathin seems to contribute to the antioxidant capabilities of rooibos,21 but aspalathin is not as well studied as quercetin and luteolin. Nothofagin is similar in structure to aspalathin and may have similar antioxidant capabilities.
Joubert says that chief research technologist Petra Snijman of the Program on Mycotoxins
and Experimental Carcinogenesis (PROMEC) at the Medical Research Council of South
Africa recently developed a way to isolate pure aspalathin and nothofagin from rooibos.
Joubert says, "According to unpublished in vitro studies done at ARC Infruitec-
According to the data in Table 1, a 150 ml serving of fermented rooibos made with 2.5 g of tea leaves has about 3 mg of aspalathin; since the amount of nothofagin was measured to be three times less than aspalathin in one study,20 a 150 ml serving of fermented rooibos has on the order of 1 mg of nothofagin. A serving of unfermented rooibos has considerably more aspalathin and nothofagin than an equal serving of fermented rooibos because a portion of these flavonoids oxidizes to other substances during fermentation.20
Orientin and Rutin: Orientin and rutin are two of the other most abundant monomeric
flavonoids in rooibos,19 and both have been associated with health benefits. Orientin
is a potent free radical scavenger. It reduced by half the number of cancer-
Total Antioxidant Capability: Although the 10 flavonoids in Table 1 are important because they are known to have antioxidant properties, they only represent a small percentage of the total polyphenol content of a serving of fermented rooibos tea. A 150 to 200 ml serving of rooibos can have up to 60 to 80 mg of total polyphenols,22 and Table 1 shows that a 150 ml serving of fermented rooibos made with 2.5 g of leaves has about 14 mg of the 10 flavonoids in the table. Many other polyphenols are present, but they have not all been identified or quantified.
To assess the antioxidant capability of rooibos tea as a whole, researchers compared
the antioxidant activity of rooibos tea extracts to that of green and black tea extracts
with the DPPH radical scavenging assay as well as the beta-
In this study, all the tea extracts were diluted to the same amount of soluble solids
rather than to the amounts of solids found in the teas.47 This method allows a comparison
of antioxidant capability on a mass equivalent basis, but does not reflect a comparison
of the antioxidant strength of equal volume servings of the teas. Although the soluble
solid content varies with the method of tea preparation, it usually decreases in
the order green tea, black tea, unfermented rooibos, fermented rooibos.47 The percent
of soluble solids represented by polyphenols is similar for the four teas and the
DPPH antioxidant activity is similar on a mass equivalent basis, so the DPPH antioxidant
capability of equal-
The studies referenced above show that rooibos tea contains antioxidants that have positive effects when tested as isolated substances and that the tea as a whole has good antioxidant activity in vitro. So, do all these antioxidants in rooibos tea lead to health benefits for tea drinkers?
Rooibos Research in Live Animals and Animal Cells
Laboratory studies have demonstrated potential health benefits of rooibos in vitro (in test tubes) and in vivo (in live animals), but human studies have not been conducted. Much more research is needed, but the studies so far look intriguing.
Fermented Rooibos against Mutagens: Researchers found that fermented rooibos tea
Both green tea and rooibos tea suppressed aberrant cells caused by B(a)P and MMC in the presence of S9, but rooibos showed a greater suppression of aberrant cells than did green tea (see Table 2). In fact, when the cells were exposed to B(a)P and S9 simultaneously with rooibos tea, the highest concentration of rooibos tea (1000 microgram/ml) completely inhibited the aberrant cells, bringing their percentage down to the level of the controls that were not exposed to any mutagen. Also, rooibos tea suppressed aberrant cells caused by MMC both with and without the presence of S9, but green tea showed no suppression without S9. Treating the cells simultaneously with the mutagen and tea extract caused a greater protective effect than treating the cells with tea extract following exposure to the mutagen (compare Tables 2 and 3).
In the in vivo part of this study, mice were given oral doses of tea and an injection of B(a)P or MMC.48 The researchers measured the frequency of micronucleated reticulocytes (MNRETs), which are cells with damaged DNA that may lead to cancer. In one experiment, a single oral dose of tea (1 ml of 0.2 percent green tea or 0.1 percent rooibos tea) was given 6 hours prior to an injection of MMC and the number of MNRETs was counted at 24, 48, and 72 hours after the MMC. Rooibos tea and green tea provided similar inhibition of the frequency of MNRETs. After 48 hours, rooibos tea reduced the level of MNRETs by about 34 percent, and green tea reduced the level by about 38 percent. When the mice received the single dose of tea either after the mutagen or 24 hours prior to the mutagen, neither green tea nor rooibos tea reduced the frequency of MNRETs.
When the teas were given as one oral dose daily for 28 days and then the mutagen was injected on day 29, both rooibos tea and green tea reduced the frequency of MNRETs caused by B(a)P. Daily doses of 0.2 percent green tea reduced MNRETs by about 62 percent 48 hours after B(a)P exposure, and daily doses of 0.1 percent rooibos tea reduced MNRETs by about 49 percent. Daily doses of 0.1 percent rooibos tea reduced MNRETs by about 34 percent 48 hours after MMC exposure, but daily doses of green tea did not provide a significant reduction with MMC.
Fermented Rooibos against Irradiation: Another research group found that extract
of fermented rooibos tea reduced cancerous transformation of mouse cells exposed
Fermented Rooibos against Brain Lipid Peroxidation: Rats given fermented rooibos
tea daily ad libitum (free access) from the age of 3 months to 24 months had greatly
The authors give a bar chart that summarizes the TBARS data for each area of the
brain.50 The TBARS values in nmol/g for 24-
Fermented vs. Unfermented Rooibos: Another study found that both fermented and unfermented
rooibos tea exhibits antimutagenic properties in vitro as measured by the Salmonella
typhimurium mutagenicity assay with several different mutagens; the antimutagenic
activity was stronger against the metabolically activated mutagens 2-
One of the authors of both these studies is senior research scientist Jeanine Marnewick of the Program on Mycotoxins and Experimental Carcinogenesis (PROMEC) at the Medical Research Council of South Africa. She says, "Rooibos showed protective effects against DNA damage when tested in an in vitro assay as well as in an in vivo animal system." 53 The in vitro studies found unfermented rooibos was generally more protective against DNA damage than fermented rooibos. But Marnewick says her group’s research shows that fermented rooibos has a stronger effect against some mutagens. She says, "Both the fermented and unfermented rooibos showed a significant protection, and we’re busy elucidating the mechanisms."53 She is currently evaluating the protective effect of rooibos on liver, esophageal, colon, and skin cancer induced in live animal models. The studies are in the early phases and she cautions, "Very little is known about the effect of rooibos on cancer development." 53
Joubert also adds a cautionary note, saying that many questions about rooibos still need to be answered.22 She says that researchers need to determine which of the antioxidant substances in rooibos tea are absorbed by the body and how much tea is needed to produce a measurable benefit. She also emphasizes that no human studies have been conducted yet.
Whole Foods vs. Isolated Antioxidants: The full benefits of teas are likely to come
from a combination of all the antioxidants in them rather than from just one substance.
Quite a few studies have found that isolated antioxidants don’t have as positive
an anticancer effect as the mixture of antioxidants found in natural food sources;
whole apple extracts were better than pure quercetin at inhibiting the growth of
cancer cells in vitro,13,54 tomato powder was better than pure lycopene at extending
the life of rats with prostrate tumors,13,55 and freeze-
Rooibos Folklore: What’s Proven?
Although rooibos does contain active antioxidants, many of the other health claims made for rooibos tea are not well documented (based only on anecdotal evidence) or are not supported by science. Researchers are still investigating many of these claims to evaluate all the potential benefits of rooibos.
Vitamins And Minerals: Despite some promotional claims that rooibos is a source of vitamin C, Joubert says it is not. "We have tested both the traditional rooibos and green rooibos, and vitamin C was not present," she says.22
With the exceptions of fluoride and copper, the trace amounts of minerals in rooibos are not enough to make the tea a meaningful dietary source of minerals for the average consumer. As shown in Table 5, the nutritional labeling that is given on some packages of rooibos tea and on some websites of distributors4,5 indicates that the amounts of iron, potassium, zinc, calcium, and magnesium in a 200 ml serving of rooibos tea are all less than 1 percent of the U.S. reference daily intake (RDI). A 200 ml serving of rooibos provides over 5 percent of the RDI of fluoride for adults and over 7 percent of the RDI for copper (see Table 5). Marc S. Micozzi, M.D., Ph.D., director of the Policy Institute for Integrative Medicine in Bethesda, Maryland, notes that when rooibos is used as a fluid replacement throughout the day, as is done with some athletes in South Africa, it does provide measurable amounts of several minerals and electrolytes.58
Colic, Allergies, And Other Ailments: Distributors of rooibos tea often suggest it
can help allergies, sleep problems, digestive problems, headache, and other ailments,4,5
but these claims have not been verified by scientific research. If the indigenous
people of the Cedarberg region used rooibos tea medicinally, that tradition was lost
and rooibos was just enjoyed as a good-
Today, South African physicians recommend rooibos for infant colic.59 South Africans also use it to calm digestive upset in adults, to help induce sound sleep, and topically to sooth eczema, skin allergies, and diaper rash.59 Not enough research has been done to know if these folk remedies really are effective or to identify the substances in the tea that might be responsible for any observable benefits. Joubert says the tea does seem to help infant colic, but no formal studies have been done.22
Immune Function: An in vitro and in vivo study showed that rooibos might enhance immune function, but very little research has been done on this topic.60 One study found that a polysaccharide in rooibos leaves may have antiviral activity against the HIV virus, but the polysaccharide had to be chemically extracted from the leaves and is not found in tea made by steeping the leaves in water.61 There’s no evidence that rooibos tea fights the HIV virus.
Zero Caffeine And Low Tannin: Several other health advantages of rooibos tea that
are often mentioned are its zero caffeine content and its low tannin content. Because
rooibos is naturally caffeine-
Rooibos only has about 4.4 percent tannin content,51 which means that it does not
have the astringent taste associated with C. sinensis and will not become bitter
even after long steeping times. Rooibos tea can be a good alternative to C. sinensis
for people who prefer the milder taste of a less astringent herbal tea or for those
who have digestive problems with tannin-
Iron Absorption: Other disadvantages have been attributed to tannins; they can bind
The low tannin content of rooibos is sometimes used to infer that rooibos tea won’t inhibit iron absorption, but that conclusion is not automatic since rooibos is rich in other polyphenols that might decrease iron absorption. In one small study, three groups of 10 young healthy men were given an oral dose of iron, followed by rooibos tea, C. sinensis tea, or plain water.71 Iron absorption was measured to be 7.25 percent for rooibos tea, 1.70 percent for C. sinensis tea, and 9.34 percent for plain water. The result for C. sinensis was significant (P < .0001), but the data for rooibos did not reach statistical significance (that is, the data for rooibos were not good enough to determine whether this result can be generalized to the whole population or whether the result was just chance). More studies are needed to better document the effect of rooibos on iron absorption, but this study implies that rooibos might not inhibit iron absorption nearly as much as C. sinensis tea.
The Bottom Line
Rooibos tea has become popular because of its fruity, sweet taste and its caffeine-
The author thanks Elizabeth Joubert, Ph.D., specialist researcher at South Africa’s
Laurie Erickson, a freelance writer in Mountain View, California, is interested in the medicinal and horticultural aspects of herbs. She began investigating rooibos out of personal curiosity and has no financial connections with the rooibos industry. Her educational background includes a B.S. in Environmental Earth Science and an M.S. in Geomechanics from Stanford University. She has also written the medical website <> and has been published in the garden section of several newspapers.
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