Herbal health remedies, used by millions of people around the world for thousands of years, may not be as safe as believed, as a new study suggests that some herbs may contain toxic or cancer causing substances.
Many believe that herbs are safe because they have been used for many years, but researchers from Baylor College of Medicine and Stony Brook University in US found that long-term use of herbal remedies is no guarantee of their safety.
Researchers showed that the plant Aristolochia can cause aristolochic acid nephropathy (AAN), a condition that leads to interstitial nephritis, renal failure and urinary track cancers.
In Taiwan, according to the national prescription database, between 1997 and 2003, 8 million people were exposed to herbals containing Aristolochia.
Studies of patients with renal failure and cancer in Taiwan and China show that tens of millions of people in those countries are at risk of AAN.
In genetically susceptible people, consuming Aristolochia can lead to the formation of complexes between aristolactam, a compound in Aristolachia, and DNA in renal tissues.
These complexes lead to mutations in the TP53 tumour suppressor gene, which may trigger kidney cancer.
Additional studies have shown that the process may lead to the development of cancer in the liver and the bladder.
Researchers indicate that other herbals and traditional medicines are responsible for severe adverse events in Africa and Asia, but in these cases epidemiological data are lacking.
Although Aristolochia has been used as a herbal remedy for more than 2,000 years, the intrinsic toxicities were not recognised owing to the latency period between exposure and the onset of symptomatic disease and to genetic determinants that confer susceptibility to only about 5 per cent of those exposed to this herb, the researchers said.
The long-term scientific study of AAN showed the association of the disease with Aristolochia.
Almost all carcinogens and many toxins require a long period of time before symptoms appear.
This makes it very difficult for a layman or a professional to identify a particular compound as the cause of an illness when it was taken months or years earlier.
"The history of Aristolachia indicates that other herbs that have been used for a long time may also have toxic and/or carcinogenic compounds," the researchers said.
"It is prudent to assume that many herbs may contain toxic or carcinogenic substances that can cause subsequent health problems for humans," they said.
The researchers disagree with the World Health Organisation's endorsement of traditional herbal remedies on the premise that traditional medicine is of proven quality, without mentioning the lack of scientific evidence supporting the efficacy of herbal remedies or their demonstrated hazards, as in the case of Aristolochia.
