Hibiscus leaf is a rich source of polyphenols which are thought to have hypolipidemic (lipid-lowering) and antioxidant effects. Approximately 15-30 percent of the hibiscus plant is made up of plant acids, including citric acid, malic acid, tartaric acid and allo-hydroxycitric acid lactone -- i.e. hibiscus acid, which is unique to hibiscus.
Other chemical constituents are many; however, some of the most important include alkaloids, anthocyanins, and quercetin.
In Ayrvedic medicine hibiscus is used to cure cough and hair loss. Chinese medicine has many uses for hibiscus flowers and roots. A 2011 study shows that hibiscus has potential as a skin treatment and skin protection agent, since it is observed that it absorbs ultraviolet radiation. Some recent studies show that hibiscus tea can lower high blood pressure.
A study conducted in Portugal found that drinks containing hibiscus exhibited higher antioxidant activity than other beverages.
The scientists, led by Chun-Tang Chui from the Institute of Biochemistry and Biotechnology in Taiwan, claimed that this was the first study focusing on the polyphenols and their anti-melanoma mechanisms.
Melanoma is the least common but most fatal form of skin cancer and is resistant to most forms of treatment including chemotherapy. Rates of melanoma have doubled in the past 20 years.
"Melanoma has become an increasingly important public health issue and novel treatment options have become an important medical need," say the researchers.
There are more than 70,000 cases in the US alone every year and almost 10,000 people will die of the disease yearly. Melanoma accounts for less than two percent of skin cancer cases, but the vast majority of skin cancer deaths. Of the seven most common cancers in the US, melanoma is the only one whose incidence is increasing.
Exposure to sunlight and ultraviolet light has been repeatedly shown to not be the cause of skin cancer. Scientists from The University of Texas MD Anderson Cancer Center reported UVA exposure is unlikely to have contributed to the rise in the incidence of melanoma over the past 30 years.
"Regarding the effect of Hibiscus leaf in vitro and in vivo studies, the effect of the polyphenolic extract in cancer is rarely reported. Thus, it is important to evaluate the potential of Hibiscus leaf polyphenols (HLP) as a functional food for anticancer."
Chui et al. said that hibiscus leaf was consumed as a vegetable in Africa but ignored elsewhere around the world. They suggested that based on these results, published in the Journal of Food Science, HLP may be a useful anti-melanoma agent.
Using human melanoma cells, mice melanoma cells and normal human skin fibroblasts as a control, the researchers treated them with various concentrations of HLP for 24 hours in order to determine the effect on the cancer cells as well the mechanisms behind this.
They found that HLP, and in particular the polyphenol epicatechin gallate (ECG), had an inhibitory effect on the growth of both the human and mouse cancer cells -- inhibiting 50% of cancer cell viability when treated for 24 hours at a 250 microgram per millilitre (mL) dose. Significantly, the normal human skin cells did not change.
"These findings indicate that the HLP is likely to be a useful chemotherapeutic agent to eliminate cancer cells without significant harmful effects on normal cells," said the researchers.
They also found that HPL and ECG led to "dose dependent and significant" levels of cancer cell death in the human cancer cells, in two ways -- apoptosis, or programmed cell death and autophagy, or the catabolic breakdown of cells.
The scientists have called for more research into the extraction methods to yield a maximum amount of HLP.
The safety profile of hibiscus is excellent, with no proven adverse reactions.
It is difficult to clarify dosing recommendations when different products are used in different studies. However, positive studies used the following dosages: