and Cancer-modulating Properties of Two Unique South African Herbal Teas,
Rooibos and Honeybush.
Grown only in the Cedarberg
area of South Africa's Western Cape Province, Aspalathus linearis,
a woody legume, is cultivated for the production of rooibos. The needle-like
leaves and stems are used to manufacture rooibos tea which has been used as
herbal beverage and to a lesser extent, as herbal medicine, in South Africa
since the 1800’s. The indigenous Khoi people were the first to use rooibos
as an herbal beverage. The popularity of this herbal tea can be ascribed to
the low tannin content and absence of caffeine. It is harvested during the
hot summer months. The plant cuttings are bound, milled, wetted and bruised
by rollers to stimulate chemical oxidations/"fermentation", during
which the distinctive colour, aroma and flavour develop. The processed tea
is sun dried, graded, pasteurized and packed for the local and export markets.
Honeybush tea (Cyclopia intermedia), another traditional South African herbal
beverage receiving prominent attention, occurs in certain regions of the Western
and Southern Cape. The earliest mention of the honeybush plant in botanical
literature was in 1705. Honeybush tea is made from the leaves, stems as well
as flowers of several species of Cyclopia.
The phenolic constituents
of rooibos and honeybush teas differ from each other as well as from that
of green and black teas (Camellia sinensis). The absence of caffeine
in rooibos and honeybush teas and the low tannin content contributes to their
popularity as health beverages. Several health-promoting properties have been
associated with the consumption of rooibos tea and to a lesser extent honeybush
tea, e.g. as treatment for colic infants, as aid for allergies, sleep and
digestive disorders etc. It has been suggested from these health issues that
rooibos tea is a more suitable beverage for infants as opposed to soft drinks
containing high levels of caffeine. However, no formal scientific research
has been conducted to substantiate the health claims to confirm this.
Scientists have identified
that cancer development is a multi-step process and that damage to genetic
material (DNA) is likely to be a major cause of cancer and other chronic diseases.
Both rooibos and honeybush teas have been shown, in studies done at PROMEC
Unit, to prevent DNA damage. These herbal teas showed protective effects against
chemical-induced mutagenicity in vitro as well as in vivo.
The activity of two drug detoxifying enzymes, glutathione-S transferase (GST-)
and UDP-glucuronosyltransferase (UDP-GT) were significantly induced in the
liver of rats consuming the herbal teas at concentrations (2% for rooibos
and 4% for honeybush) customarily used for tea making purposes in South Africa.
Several mechanisms involved in this ex vivo protection can be suggested:
1) the phase II detoxifying enzyme, GST-,
catalyse conjugation of glutathione (GSH) to a variety of electrophillic compounds
(e.g. chemical carcinogens) thus mediating a protective effect against carcinogenesis
or mutagenesis. The ratio of reduced (GSH) and oxidised (GSSG) glutathione
in the livers of rats consuming the two herbal teas were 5-6 fold higher.
Reduced glutathione is a powerful intracellular antioxidant and the ratio
of reduced to oxidised glutathione serves as a marker of the antioxidative
capacity of the cell. The increased ratio may be indicative of a reduced oxidative
stress in the liver as compared to control rats drinking water, 2) the increased
glucuronidation capacity of the liver also contributes to the deactivation
of mutagens/metabolites that may serve as precursors for the ultimate carcinogen
and 3) the presence of tea phenols in the liver cytosol may also interfere
with the metabolic activation of carcinogens, thus contributing to the protective
effect. The herbal teas had no effect on the level of the Phase I activating
enzymes in the liver.
Further studies are conducted
at the PROMEC Unit in collaboration with the ARC Infruitec-Nietvoorbij (Stellenbosch,
South Africa) to elucidate the health promoting properties of these two unique
South African teas with regards to cancer prevention.