Be careful with those Vitamin C pills: Antioxidants fuel cancer, warn Hong Kong scientists – South China Morning Post (subscription)
Antioxidants, long trumpeted as health boosters and sold in supplements, have been found to hasten the growth of liver cancer, the city’s third-deadliest cancer.
A University of Hong Kong study – likely to impact on the multibillion-dollar health supplements industry – also shed light on a new treatment approach for the cancer, which killed more than 1,500 Hongkongers in 2013.
Among the 500,000 to one million new cases reported around the world every year, more than half were in China.
Antioxidants combat free radicals, which damage human cells, but the research team found that they were also necessary for the growth of cancer cells.
“It might just be half true that antioxidants are beneficial to health, as cancer cells also need a lot of antioxidants,” said Dr Carmen Wong Chak-lui, assistant professor at the university’s department of pathology.
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In the study, liver cancer cells were found to produce more antioxidants, which assisted tumour growth, through an enzyme called transketolase.
Other kinds of cancer, including colorectal and lung cancers, were also seen to have a similar metabolic pattern.
“External supplements might help stabilise the [antioxidants] produced by the cancer cells,” Wong said.
Cancer patients might take antioxidant supplements such as vitamin C tablets for extra nutrients, but the researchers raised a big question mark about doing so.
“[Cancer patients]might not have to stop taking it, but they need to consider whether it is necessary to continue,” said Professor Irene Ng Oi-Lin, who led the study.
Healthy people should also be wary of taking health supplements that have a high concentration of one particular nutrient.
“We don’t have data concluding supplements are carcinogenic. But we don’t know whether we have hidden cancer cells that might be triggered by the supplements,” Ng said.
She said one supplement tablet might contain 500 to 1,000 milligrams of Vitamin C, far exceeding the 100mg necessary for an adult every day.
The research team insisted they were not targeting any specific supplements and the findings apply to cancer patients only.
Patients should also not stop eating fruit such as oranges, lemons and papayas that were rich in antioxidants, they said.
“Apart from vitamins, fruit also contains other kinds of nutrients that patients need. They should refrain from taking too many health supplements,” Wong said.
Gordon Cheung Chi-leung, president-elect of the Nutrition Association, said an antioxidant-high diet was not recommended for cancer patients. “We are concerned more about the energy and protein intakes for cancer patients … as they might experience weight loss,” Cheung said.
“For [healthy people] or cancer survivors, a plant-based diet with less meat is recommended to prevent cancer.”
Dr Stephen Chan Lam, a Chinese University oncologist specialising in liver cancer, said he did not particularly encourage patients to eat more fruit as no data had proved its effectiveness. But around half of his patients would take extra supplements along with Western medication.
“Patients have to communicate with doctors if they want to take supplements. Their liver might not be able to handle it if it is not working well,” Lam said.