The implications are particularly relevant in South Africa where skin cancer is the most common form of cancer with 20,000 reported cases annually and 700 deaths. This is the second highest incidence in the world after Australia.
If treated early and effectively, skin cancer can be arrested or cured, but low compliance and the expense associated with many existing treatments results in a high recurrence rate. This has led researchers and scientists here and internationally to investigate other options and the use of plant polyphenols is showing promise.
Counter the effects of UVB
Polyphenols are known to be anti-inflammatory, moderate the immune system – preventing the aggressive response that can lead to tumours - and anti-oxidant. This is an ideal combination to counter the effects of UVB, the band of ultraviolet radiation that acts as a cancer initiator and promoter. The skin possesses defences to protect itself, but excessive exposure to sunlight suppresses immunity and overwhelms these.
South African researchers from the Medical Research Council’s PROMEC Unit and the Oxidative Stress Research Centre at the Cape Peninsula University of Technology presented the results of two recent studies at the third annual Rooibos Science Café. The studies were part of a master's thesis, and have not yet been published in any academic journal.
The Rooibos Science Cafés showcase the latest local and international research into rooibos' health benefits and potential applications and also provide an update on some of the studies that the South African Rooibos Council is funding.
Professor Jeanine Marnewick and her team from the Cape Peninsula University of Technology, studied the effect of herbal tea extracts 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 resulting from chronic UVB exposure. "One can not directly extrapolate animal data to humans, but it surely gives the scientist a very good indication as what could happen in humans," said Marnewick.
It found that green or unfermented rooibos reduced the number of tumours per mouse by 75% and fermented rooibos by 91%. The equivalent findings for honeybush were 86% and 64% respectively. The study also found that green rooibos shrunk the size of the tumours by 91% and fermented rooibos by 97%. The result for the green honeybush was 91% and 95% for fermented honeybush.
The conclusions of the chronic UVB study are that polyphenolic-rich extracts from rooibos and honeybush have 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.
The MRC study aimed to find out more about how herbal teas affect the factors influencing the survival of cancer cells, an essential step in the road to creating an effective anti-cancer product.
The study used a dual approach. The first phase looked at how herbal tea extracts may counter UV inflammation. It did this by using a molecular marker that signals the start of inflammation. 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 have the ability to reduce the production of a marker of early inflammation in cells exposed to UV light. Rooibos did not affect production of this specific marker, but might possibly act on different levels in the inflammatory response. Rooibos exacerbated cell death in UV exposed cells, which could play a role in cancer prevention. It also concluded that rooibos may prevent skin cancer by delaying the progression of abnormal cells, interfering with their growth and viability.
Further studies needed
While the study is another important step in discovering the potential of rooibos and honeybush to prevent and treat cancer, the researchers point out that there is still more work to be done as the cancer-prevention properties are not entirely related to the polyphenolic compounds. Before developing a product to prevent skin cancer other constituents in the tea will need to be studied.
Although the study author is hesitant to comment on the use of any specific Rooibos products in the fight against skin cancer, Marnevick does suggest making Rooibos part of your daily health regime. "Taking into account these results together with other scientific results on rooibos and it's possible health promoting properties we recommend that rooibos should be made part of your daily healthy regime for prevention."
The SA Rooibos Council invests some R1 million in research and is currently supporting research projects at several local universities and science councils on how rooibos can counter cancer and oxidative stress as well as the link between rooibos and exercise. A project on rooibos and obesity has been approved for funding in 2011.
Updates on rooibos research and health news can be found at www.rooibosforlife.com.
- Health24, December 2010