Self-medicating with antioxidants could boost tumor cells, studies show

When it comes to cancer, special care must be taken when self-medicating with antioxidants, according to a University of Hong Kong (HKU) research team.

Director of State Key Laboratory for Liver Research (HKU) Irene Ng Oi-lin said cancer patients should take note that a high intake of antioxidant supplements might not be beneficial to people's health.

Taking antioxidants was a balancing act, Ng said, noting cancer cells could be repaired with proper vitamins. But dousing them with antioxidants stimulated responses where test tumor cells actually benefited from an environment of excessive antioxidants.

Similar risks existed for colorectal, rectal, bladder, gastric, ovarian, lung and prostate cancers, Ng said.

She said the average person only needed about 40 mg to 120 mg of Vitamin C daily, from newborns to breastfeeding mothers. Antioxidant supplements such as Vitamin C pills are available over the counter in 1 gram single doses.

For Vitamin C, 100 grams of a regular orange is sufficient to fulfill 64 percent of the body's daily recommended intake. But this only provides 1 percent of the body's daily recommended intake of Vitamin A, according to the United States Department of Agriculture (USDA).

"It might only be half true that antioxidants are beneficial to health, as cancer cells also need a lot of antioxidants," assistant professor at HKU's Department of Pathology, Carmen Wong Chak-Lui, said.

In tested cancer cells, Ng's team found an enzyme called transketolase interacted with antioxidants to speed growth, while test batches where the enzyme was suppressed were up to 40 percent smaller.

Liver cancer is the third-most common cancer-related cause of death in Hong Kong, after lung and colorectal cancer, according to Hong Kong Cancer Registry figures.

The majority of liver cancer patients are aged over 40, with 80 percent being carriers of hepatitis B, Ng said.

The anti-cancer effects of antioxidant-loaded fruit juices have been an important marketing point for decades. A multibillion-dollar international market has been built on supplements.

tim@chinadailyhk.com

(HK Edition 02/19/2016 page8)