The rooibos plant, already found to reduce the threat of heart disease and stroke, has been shown to also help prevent skin cancer.
Two studies undertaken by local researchers have found that rooibos has properties which can effectively reduce skin tumours caused by harmful exposure to UVB rays – the band of ultraviolet radiation that acts as a cancer initiator and promoter.
One study was conducted by the Medical Research Council’s Promec unit, and the other by the Oxidative Stress Research Centre at the Cape Peninsula University of Technology (CPUT).
Both studies received funding from the South African Rooibos Council.
At a meeting of the council in Joburg recently, researchers revealed that the plant’s polyphenols, which are known to be anti-inflammatory, moderate the immune system. This, they said, could prevent the immune system’s aggressive response to UVB that could lead to tumours.
Lead researcher of the CPUT study, Professor Jeanine Marnewick, and her team studied the effect of extracts of the herbal tea on UV-induced skin tumours in mice.
One of the objectives was to establish whether rooibos and honeybush reduced the number, size and volume of tumours.
They found that green or unfermented rooibos reduced the number of tumours per mouse by 75 percent. The figure for fermented (crushed) rooibos was 91 percent.
The equivalent findings for honeybush were 86 percent and 64 percent respectively.
The study also found that green rooibos shrunk the size of tumours by 91 percent and fermented rooibos by 97 percent. The result for the green honeybush was 91 percent and 95 percent for fermented honeybush.
The conclusions of the study were that polyphenol-rich extracts from rooibos and honeybush had anti-tumour and photoprotective properties.
“This indicates potential for use in cosmeceuticals for sun protection, and as part of a strategy for preventing non-melanoma skin cancers in humans,” said Marnewick.
The MRC study aimed to find out more about how herbal teas affect the factors influencing the survival of cancer cells.
Researchers said the first phase of the study looked at how herbal tea extracts may counter UV inflammation, while the second phase examined how rooibos and honeybush extract affected the survival of cancer cells, by studying the effect on their viability and growth.
The MRC team found that some of the honeybush teas had the ability to reduce the production of early inflammation in cells exposed to UV light.
“Rooibos exacerbated cell death in UV-exposed cells, which could play a role in cancer prevention. (The study) also concluded rooibos may prevent skin cancer by delaying the progression of abnormal cells, interfering with their growth and viability,” the researchers concluded.
While the studies were an important step in discovering the potential of rooibos and honeybush to prevent and treat cancer, researchers pointed out there was more work to be done because the cancer-prevention properties were not entirely related to polyphenolic compounds.
“Before developing a product to prevent skin cancer, other constituents in the tea will need to be studied,” said Marnewick.
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