The first-ever human clinical trial on a
popular traditional South African herbal tea was recently conducted, testing
whether the tea can possibly lower the risk of cardiovascular
disease.
The new trial also generated the first human
safety data in a controlled clinical trial environment, scientifically showing
that short-term consumption of rooibos tea is safe for the liver and kidneys
while keeping various blood parameters (e.g., blood pressure, cholesterol
levels, etc.) in a normal range.1
Provisional results from this study indicate
that rooibos tea protects the body against oxidative damage, as seen by the
approximate 21% decrease in conjugated dienes in the blood. Conjugated dienes
are products formed in large numbers during the early stages of oxidation
(destruction) of important cellular components such as fats (lipids). These
lipid peroxidation products may be implicated in the development of vascular
disease.
The trial (entitled “Modulation of blood
oxidative stress markers and DNA damage by rooibos tea in volunteers at risk
for coronary heart disease”) was conducted by Jeanine L. Marnewick (PhD),
senior researcher at the Oxidative Stress Research Centre at Cape Peninsula
University of Technology in Cape Town,
South Africa.
The trial was conducted on 40 individuals
(males and females), between the ages of 30 and 60, from the Western Cape
Province with any two or more of the following cardiovascular disease risk
factors: hyperlipidemia (high cholesterol), hypertension (high blood pressure),
smoking, and/or increased body mass index (BMI; 20 - 35), but not requiring any
oral medication for these medical conditions. The actual risk of each participant
was determined using a calculation based on the famous multi-year Framingham
heart disease trial based on the patient’s age, gender, smoking status, blood
pressure, triglycerides and HDL cholesterol (so-called “good cholesterol”). A
person with 2 major risk factors has a risk of heart disease or stroke 6 times
as great as a person with no risk factors. With 3 factors, the risk of
cardiovascular disease is 20 times as great.
Participants in this trial were required to
consume 6 cups of rooibos tea per day for 6 weeks with the 6-cup intake spread
across the day. In order to maintain a high degree of consistency, the
preparation of the rooibos tea was standardized as 2% weight of dried rooibos
tea to volume of water, with each cup consisting of one rooibos tea bag with
the addition of 200 mL of boiling water (equal to about 7 ounces, slightly less
than 1 cup), brewing for 5 minutes before consumption. Subjects consumed the
rooibos with or without milk and/or table sugar, as previous research on green
and black teas (from the tea plant, Camellia
sinensis) have demonstrated that milk does not eliminate the
increase in plasma antioxidant activity in humans.2 (The class of
beneficial antioxidant chemicals found in rooibos, black and green tea, and
chocolate are called flavonoids; the flavonoids in rooibos are different from
those in tea and chocolate.) The 6-cup amount of rooibos consumed by
participants in this trial was based on a human trial published in 2003 where
the consumption of 6 cups of green tea increased the antioxidant capacity in
the blood of human subjects.3
In a study of this type, it is important to
modify the diet of participants in order to remove the consumption of other
flavonoid-rich foods which may confuse the study results. To do this, the
participants were requested to omit flavonoid-rich beverages (red wine, black
or green tea and/or herbal teas, coffee, fruit juices, etc.) and to restrict
flavonoid-rich foods (grape products, citrus fruits and their juices, berries
and their juices, apples, onions, broccoli, etc.) from their diet for 2 weeks
before initiation of the intervention study. (Analysis of participants’ fasted
blood and urine samples taken after this period served as a baseline standard
to help determine the extent of participant compliance with the study
guidelines.)
As a quality control for the rooibos, a large
quantity of rooibos of the same batch was obtained from Rooibos Ltd., the major
rooibos producer and supplier in Clanwilliam,
South Africa.
To ensure consistent quality the researchers took random samples of the rooibos
from this one large batch and analyzed them for key chemical compounds (e.g.,
flavonols) and antioxidant capacity.
The clinical trial design and some of its
initial results were announced in a presentation by Dr. Marnewick at the World
Tea Expo in Las Vegas, Nevada in May. The trial paper will be
submitted to a medical journal for publication after all the statistical data
has been fully analyzed, probably by the end of this year.
“Despite its long history of traditional use
in South Africa and growing popularity around the world as a tasty and
healthful beverage, this is the first time that rooibos has been subjected to a
tightly controlled human clinical trial to determine its potential benefit
in reducing cardiovascular disease factors,” said Mark Blumenthal,
founder and executive director of the American Botanical Council, the leading
nonprofit organization dealing with herbs, medicinal teas, and related
plant-based ingredients.
“With cardiovascular disease being the
biggest killer of people in North America and
elsewhere in the world, this study’s preliminary positive results may help
increase the relevance of rooibos as a beneficial beverage for consumers and
healthcare providers seeking safe, low-cost ways to reduce cardiovascular
disease risk,” he added.
Members of the tea industry welcomed the
preliminary research findings. “We are extremely excited about the preliminary
results of this clinical trial”, says Hugh Lamond from Herbal Teas
International of Anaheim, California, the largest distributor of rooibos in North America. “The trial appears to confirm the
anecdotal promise for rooibos in fighting heart disease and reducing oxidative
stress in humans. As a result, we expect a huge boost in the worldwide
consumption of rooibos in the coming years.”
The research was conducted at the following
South African institutions: Cape Peninsula University of Technology and the University of Cape Town. Funding was provided by Cape
Peninsula University of Technology, THRIP National Research Foundation, and the
South African Rooibos Council.
Note: The American Botanical Council advises that with all scientific and
clinical research that has yet to be published in a peer-reviewed journal, the
preliminary announcement of trial results and related statistics may eventually
be modified as a result of the peer review process. Thus, some of the data
reported in this news release are subject to revision upon publication of this
trial.
About Rooibos
Rooibos (Aspalathus linearis) in the pea family (Fabaceae) is a
popular beverage from South
Africa. The name comes from the local
Afrikaans name for “red bush,” referring to the red-auburn color of the plant
material, which changes after it is harvested and allowed to ferment. The
pleasant-tasting red-colored beverage is high in antioxidant compounds, which
have been shown to be beneficial for cardiovascular health, among other
benefits. Rooibos does not contain any natural levels of caffeine. A
comprehensive review of the history and scientific publications of rooibos was
published in the American Botanical Council’s quarterly journal, HerbalGram
(issue #59) in 2003.
References
1. Marnewick JL. Rooibos Power. World Tea Expo,
May 31, 2008.
2. Leenen R, Roodenburg AJ, Tijburg LB, Wiseman SA. A single dose of tea with
or without milk increases plasma antioxidant activity in humans. Eur J Clin
Nutr. 2000;54(1):87-92.
3. Rietveld A, Wiseman S. Antioxidant effects of tea: evidence from human
clinical trials. J Nutr. 2003;133(10):3285S-3292S. |