Issue: 59 Page: 34-45
Rooibos Tea: Research into Antioxidant and Antimutagenic Properties
by Laurie Erickson
HerbalGram. 2003; 59:34-45 American Botanical Council
Rooibos Tea: Research into Antioxidant and Antimutagenic Properties
Antioxidants are hot topics in the health news these days, and an herbal tea called rooibos (pronounced ROY-boss) is becoming popular partly because it is being marketed as a healthy beverage with high levels of antioxidants. The rooibos plant (Aspalathus linearis (Burm. f.) Dahlgren, Fabaceae) is a South African flowering shrub used to make a mild-tasting tea that has no caffeine, very little tannin, and significant amounts of polyphenol antioxidants. Although the tea is new to many Americans, it has been made in the Cedarberg mountain region of South Africa for generations. Distributors are promoting the tea for numerous
health benefits, citing recent studies that show some antioxidants found in rooibos tea may protect against cancer, heart disease, and stroke. What’s the evidence for these claims?
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-colored tea, which can be confusing because black tea and hibiscus herbal tea are also sometimes called red tea.
Botanical Description
Rooibos is a shrubby legume that is indigenous to the mountains of South Africa’s Western Cape.1-3 The genus Aspalathus includes more than 200 species native to South Africa.2-5 A.
linearis is a polymorphic species; various wild forms have been described, each with characteristic morphology and geographical distribution.1-3 Some forms are prostrate and remain less than 30 cm (1 foot) tall, while other forms grow erect and may reach up to 2 m (about 6 feet) in height.1-3,6 The types of wild rooibos that have been used to make tea are sometimes referred
to as the Red, Black, Grey, and Red-Brown types.1,2
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-like leaves of about 10—40 mm (0.4—1.6 inches) in length.7 The plant produces small yellow flowers in spring through early summer,6 and each flower generates a one-seeded leguminous fruit.4,5
Rooibos has adapted to coarse, nutrient-poor, acidic soil and hot, dry summers.4,5,8 In addition to a network of roots just below the soil surface, the plant has a long tap root that reaches as deep as 2 m (about 6 feet) and helps the plant find moisture during summer drought.5 As a legume, rooibos contains nodules of nitrogen-fixing bacteria on its roots; this characteristic helps the plant survive in the poor Cedarberg soils and minimizes the need for fertilizing commercial crops with nitrogen.8 The bacteria convert nitrogen dioxide to biologically useful ammonia in a process known as nitrogen fixation. The plant absorbs the nitrogen and benefits from it in exchange for providing the bacteria with food sources created from photosynthesis.
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
Historical Background
More than 300 years ago, indigenous
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-dried.
Botanists first recorded rooibos plants in 1772 when they were introduced to the
tea by the Khoi people.10
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-based Rooibos Ltd. <www.rooibosltd.co.za>, a partnership of private growers/processors and a cooperative of large and small
farmers in the area. The rooibos is sold in a variety of products in Europe, Asia, and, increasingly, America. Other South African companies that market rooibos tea products include Khoisan, Cape Natural Tea Products, and Coetzee & Coetzee. International demand for rooibos has been increasing since trade sanctions against South Africa were lifted following the demise of apartheid in the 1990s. Since 1999, the nonprofit organization Agribusiness in Sustainable Natural African Plant Products (ASNAPP, <www.asnapp.org>)
has helped small farmers in and around Wupperthal to introduce sustainable methods of rooibos cultivation that allow them to compete in the world market. ASNAPP is sponsored by the U.S. Agency for International Development, Rutgers University, and Stellenbosch University. Through Stellenbosch University, ASNAPP also helped the farmers at Wupperthal fund construction of a tea court to process rooibos.
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-like leaves and stems are usually harvested in the summer, which corresponds to January through March in South Africa.4 The plants are cut to about 30 cm (1 foot) from the ground at harvest time and begin another major growth cycle the following spring. The harvested rooibos is processed two different ways, producing two types of tea. The green leaves and stems are either bruised and fermented or immediately dried to prevent oxidation. The traditional fermented tea is processed today in much the same way as the indigenous people processed it hundreds of years ago, including the sun-drying step, but the tools are more sophisticated now.
The fermented type is called red tea because fermentation turns the leaves and
the resulting tea a rich orange/red color; this distinctive color led to the Afrikaans
name rooibos, which means "red bush." The unfermented type, often
called green rooibos, contains higher levels of polyphenol antioxidants because
fermented rooibos loses some antioxidants during the fermentation process. The
unfermented type was developed to maximize antioxidant levels in response to recent
interest in the health benefits associated with the antioxidants found
in C. sinensis teas. Unfermented rooibos tea is a tan/yellow color rather
than the rich reddish color of fermented rooibos.
Both types of rooibos tea are available plain or flavored, loose or in tea bags, organic or conventionally grown. Rooibos is graded according to color, flavor, and cut length, with the highest grade labeled "supergrade." The tea has a smooth, non-bitter flavor that is pleasant hot or chilled. The unfermented variety has a very mild "green" taste reminiscent of green tea but without the astringency; the fermented type is quite different, with a stronger sweet and fruity taste. The mild flavor of rooibos has made it popular in multi-ingredient herbal tea blends.
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.14-19 Currently, rooibos is the only known natural source of aspalathin.15 Nothofagin is similar in structure to aspalathin and has only been identified in one other natural source besides rooibos: the heartwood of the red beech tree (Nothofagus fusca (Hook F.) Oerst, Nothofagaceae), which is native to New Zealand.20
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-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay, include caffeic acid, protocatechuic acid, syringic acid, ferulic acid, vanillic acid, p-hydroxybenzoic acid, and p-coumaric acid.14,18 Using the DPPH assay, caffeic acid was just as active an antioxidant as the most potent flavonoids tested (quercetin, isoquercitrin, and aspalathin).21
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-Nietvoorbij and a rooibos expert, says that the total polyphenol content of an average 150 to 200 ml serving of rooibos tea can be as much as 60 to 80 mg, depending on factors such as the brewing time and
amount of leaves used.22 For comparison, one study found that brewing black tea leaves for 1 to 3 minutes at a concentration of 1 g leaves per 100 ml water resulted in black tea that contains 128 to 199 mg of polyphenols per 200 ml serving of tea.23 The types of polyphenols in rooibos tea are different than those in green and black teas, so the potential health benefits of the teas
cannot be compared solely on their total polyphenol content. Rooibos tea does
not contain epigallocatechin gallate (EGCG), which is a polyphenol in green tea
that has shown anticarcinogenic and antioxidant capabilities, but many of the
polyphenols in rooibos tea are also strong antioxidants.
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.24-27
Quercetin decreased primary tumor growth and prevented metastasis in a model
of pancreatic cancer.25 Luteolin and quercetin inhibited proliferation
of thyroid28 and colon29 cancer cells, respectively, in
vitro. Quercetin inhibited cyclooxygenase-2 (COX-2) expression
in colon cancer cells, which may help prevent colon cancer.30,31 Both
luteolin and quercetin can block the formation of lipid peroxides.32-34
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-Nietvoorbij, aspalathin compared well
with quercetin in terms of antioxidant activity, except in a fat medium where quercetin demonstrated much higher potency than aspalathin. What is important in these comparative studies is the test environment. Relative efficacy will depend on the test system used (the polarity of the medium, the type of free radical that needs to be scavenged, etc.)."22 Joubert co-authored a study21 that found aspalathin compared well to other antioxidants with the DPPH radical scavenging assay. The study measured the antioxidant capability of many of the flavonoids and phenolic acids found in rooibos tea and compared them to several reference standards such as alpha-tocopherol (vitamin E). The percent inhibition of the DPPH radical by quercetin, isoquercitrin, aspalathin, rutin, luteolin, and alpha-tocopherol was 98.27, 91.99, 91.74, 91.18, 90.85, and 75.10, respectively (using a 0.25 mole ratio of antioxidant to DPPH). All of the flavonoids tested showed potent hydrogen donating abilities with DPPH except for vitexin, which only had a 7.26 percent inhibition even at a 0.5 mole ratio to DPPH. 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-associated changes in cells of human blood
exposed to radiation.38 When mice were exposed to radiation, orientin
protected against lipid peroxidation in the liver and also reduced damage to the
bone marrow and gastrointestinal tract.39,40 Rutin, a flavonoid found
in buckwheat (Fagopyrum esculentum Moench, Polygonaceae) and some fruits
and vegetables, seems to help maintain the strength of capillary walls; oral rutin
as well as oral and topical o-(beta-Hydroxylethyl)-rutoside (HR) have been used
to treat hemorrhoids, varicose veins, and the lower leg edema associated with
venous insufficiency and venous hypertension.41-46 According to the
data in Table 1, a 150 ml serving of fermented rooibos tea made with 2.5 g of
tea leaves has about 2.5 mg of orientin and 3.2 mg of rutin.
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-carotene bleaching method.47 All the teas showed strong
antioxidant activity with both methods. Using the DPPH method, the ranking from
highest to lowest antioxidant activity was green tea (90.8 percent inhibition),
unfermented rooibos (86.6 percent), fermented rooibos (83.4 percent), and black
tea (81.7 percent). Green tea was significantly higher than the others (P <
0.05), but the other three teas did not differ from each other significantly with
respect to DPPH inhibition. Using the beta-carotene bleaching method, the ranking
was green tea, black tea, fermented rooibos, and unfermented rooibos. The relative
ranking varies with the type of test because the substance to be tested will have
different reactivity to the different oxidizing agents used. These tests only
measure the antioxidant capability of substances outside of the body and don’t
provide data on whether the antioxidants are absorbed by the body and effective
after the food is consumed.
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-sized servings will decrease in the order of the soluble solid content.47
Black and green teas have over twice as much soluble solids as rooibos tea when
prepared conventionally, so over two 200 ml servings of rooibos tea would need
to be consumed to receive the same antioxidant benefit (as measured by DPPH) as
one 200 ml serving of black or green tea (or the rooibos would need to be brewed
to twice the standard concentration).47 This result agrees with the
data given previously for 60 to 80 mg polyphenols for a 150 to 200 ml serving
of rooibos tea22 as compared to 128 to 199 mg polyphenols for a 200
ml serving of black tea.23
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 reduced cancer-associated changes in animal cells induced
by the mutagens benzo[a]pyrene (B(a)P) and mitomycin C (MMC) both in vitro
and in vivo.48 The in vitro part of the study measured
chromosomal aberrations in animal cells caused by exposure to the mutagens. The
cells were treated with tea extract either at the same time as the mutagen or
after the mutagen. Some of the tests used rat liver microsomal enzyme, called
S9, to provide metabolic activation of the mutagen; B(a)P requires metabolic activation,
but MMC can act with or without it.
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 to x-rays in vitro.49 The amount of protection
correlated with the dose of rooibos, and an extract concentration of 10 percent
reduced the cell transformations to a level similar to the spontaneous level of
the controls. Interestingly, green tea in equivalent concentrations did not show
any detectable protective effect. In another study, fermented rooibos tea reduced
cell damage in live mice that were exposed to irradiation two hours following
a single dose of rooibos administered by gastric intubation.34
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 reduced age-related lipid peroxide accumulation
in four areas of their brains compared to rats that drank plain water.50
Increases in lipid peroxides in the brain may damage neuronal cells and contribute
to age-related diseases.50 The lipid peroxide levels were evaluated
by measuring the amounts of thiobarbituric acid reactive substances (TBARS) in
eight regions of the brain. The 24-month-old rats that had been drinking plain
water had significantly higher TBARS in the frontal cortex, occipital cortex,
hippocampus, and cerebellum compared to 5-week-old rats, but the 24-month-old
rats that had been drinking rooibos tea had no increase in TBARS in those four
areas of the brain. The TBARS of the 24-month-old rooibos group were similar to
the TBARS of the young 5-week-old group (see Table 4).
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-month-old
rats without rooibos tea, 24-month-old rats given rooibos tea, and 5-week-old
rats, respectively, were approximately 120, 80, 80 in the frontal cortex; 115,
70, 80 in the occipital cortex; 80, 40, 50 in the hippocampus; and 115, 80, 85
in the cerebellum. The authors say these results suggest that the administration
of rooibos tea protected several regions of the rat brain against lipid peroxidation
accompanying aging. Magnetic resonance images taken of the brain were consistent
with the TBARS data.
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-acetylaminofluorene (2-AAF) and
aflatoxin B1 (AFB1) than it was against three direct-acting
mutagens.51 Further research showed that the fermentation process causes
a decrease in the antimutagenic and antioxidant activity of rooibos tea as measured
by the Salmonella typhimurium mutagenicity assay (with 2-AAF), the hydrogen
donating ability (assessed with DPPH), and the superoxide anion radical scavenging
assay.52 The researchers suggest that fermented rooibos may show less
antioxidant and antimutagenic activity because it has less polyphenols than unfermented
rooibos. One analysis showed that polyphenols represent about 41 percent of the
total solid matter in unfermented rooibos tea extract, but only about 30 percent
of the total solid matter in fermented rooibos tea extract.51
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-dried strawberries exhibited
better anticancer properties in animals than did pure ellagic acid.13,56
Also, white and green tea extracts demonstrated better antimutagenic properties
in vitro than mixtures of nine polyphenols found in the teas (mixed according
to their relative proportions in the teas).57 Researchers believe these
results indicate that other substances in the whole food products besides the
identified antioxidants probably contribute to the total anticancer effect of
the food, and that the relative amounts of all these substances could be important.
Different teas have different mixtures of antioxidants, and they will protect
against different mutagens. Sorting out all of these interactions will take time.
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-tasting beverage
until the recent interest in its health benefits.10 Many of the health
claims for rooibos tea began in 1968 when a South African woman, Annekie Theron,
found that rooibos tea eased her infant’s colic.10 As the story
goes, she found no documentation on the benefits of rooibos and began her own
experiments with local babies who had colic and allergies.10 She concluded
that rooibos helped these babies, and she published a book in 1970 titled Allergies:
An Amazing Discovery. Since then, she patented a rooibos extract that is now
used in cosmetic products, and she started her own line of health and cosmetic
products.10
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-free, it does not have
to be subjected to a decaffeination process and, therefore, does not lose any
of its polyphenol content (as occurs when green and black teas are decaffeinated).
The zero caffeine content also means rooibos can be enjoyed by those who want
to avoid the stimulating effects of caffeine and can be consumed in quantity by
those who want to use it as a fluid replacement.
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-rich beverages. And as Micozzi observes, some people can receive a higher
total antioxidant intake from rooibos than from green or black tea because the
low tannin content and caffeine-free nature of rooibos allow it to be consumed
in larger quantities.58
Iron Absorption: Other disadvantages have been attributed
to tannins; they can bind to non-heme iron (iron from non-meat sources), reducing
iron absorption, and they can decrease the metabolism and utilization of proteins.62-69
Black and green teas reduce the amount of non-heme iron absorbed by the body when
the tea is consumed at the same time as the iron source.62-66 These
effects do not cause problems for most people, but they can cause problems for
people who have nutritionally marginal diets or low intake of heme iron sources
(meats).69
Other polyphenol-rich beverages besides C. sinensis
teas can also inhibit iron absorption. One study found that the inhibition of
iron was 79 to 94 percent for black tea, 84 percent for peppermint tea, 73 percent
for hot cocoa, and 47 percent for tea of chamomile (Matricaria recutita
L., Asteraceae).62 The teas still inhibited iron absorption to the
same degree even if milk was added to them. Some of these beverages contain only
low levels of tannins, but other polyphenols in foods and beverages can also reduce
iron absorption.62,64 The ability of polyphenols to chelate prooxidant
metal ions might provide some antioxidant protection, but it can also be a disadvantage
by decreasing absorption of necessary dietary minerals such as iron.64
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-free, low tannin, antioxidant-rich status. Although more
research is needed, rooibos appears to be safe and free of side effects. The antioxidants
present in rooibos may help protect against free radical damage that can lead
to cancer, heart attack, and stroke. Unfermented (green) rooibos has a higher
amount of polyphenols than traditional fermented rooibos and generally demonstrates
higher antioxidant and antimutagenic capabilities in vitro. Future research
should reveal whether the antioxidant benefits of rooibos observed in vitro
and in animals translates into health benefits for humans.
Acknowledgments
The author thanks Elizabeth Joubert, Ph.D., specialist researcher
at South Africa’s ARC Infruitec-Nietvoorbij, and Jeanine L. Marnewick, senior
research scientist at the Program on Mycotoxins and Experimental Carcinogenesis
(PROMEC) at the Medical Research Council of South Africa, for their quotes and
technical input, as well as for providing copies of several research papers. Their
expertise on rooibos has contributed much valuable information to this article.
Lorenzo Bramati, Ph.D., research scientist at the Instituto Tecnologie Biomediche
CNR in Italy, provided helpful input and copies of several research papers. Erica
Renaud, a member of the quality control program for ASNAPP (Agribusiness in Sustainable
Natural African Plant Products) at the Center for New Use Agriculture and Natural
Plant Products at Rutgers University provided valuable input and photos. Marc
S. Micozzi, M.D., Ph.D., director of the Policy Institute for Integrative Medicine,
offered helpful review and comments. Rooibos Ltd./SunnRooibos also provided valuable
insight and photos.
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 <http://www.tendinosis.org>
and has been published in the garden section of several newspapers.
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