Vitamin C is known to have significant anti-cancer effects, but the precise reason why has not always been clear. New research has taken a further step towards discovering exactly why the vitamin has such an effect, while at the same time revealing that apples may be even better at fighting the disease.
C.Y. Lee, professor of food science and technology at Cornell University, and Ki Won Lee, Hyong Joo Lee and Kyung-Sun Kang, scientists from Seoul National University, found that vitamin C blocks the carcinogenic effects of hydrogen peroxide on intercellular communication, the first time that the mechanism by which the vitamin inhibits tumour formation had been discovered.
The researchers also discovered, however, that a phytochemical found in apples - quercetin - had even stronger anticancer activity than vitamin C.
"Vitamin C has been considered one of the most important essential nutrients in our diet since the discovery in 1907 that it prevents scurvy," said Lee. "In addition, vitamin C has several important functions in our body for the synthesis of amino acids and collagen, wound healing, metabolism of iron, lipids and cholesterol and others. In particular, vitamin C is a well known anti-oxidant that scavenges free radicals."
He added that vitamin C prevents the inhibition of gap-junction intercellular communication (GJIC) induced by hydrogen peroxide. GJIC is essential for maintaining normal cell growth, and blocking GJIC is strongly related to the carcinogenic process, especially to tumour promotion.
Hydrogen peroxide, a tumour promoter, inhibits GJIC by changing a special protein, connexin43. When rat liver epithelial cells were treated with vitamin C, Lee said, inhibition of GJIC induced by hydrogen peroxide was prevented.
Although vitamin C protects against oxidative DNA damage through its free-radical scavenging activity, Lee and his colleagues said they thought the vitamin's anti-tumour action functions through a different mechanism.
"The most powerful weapon we have in the fight against cancer is prevention," Lee said. "A diet rich in phytochemicals and vitamin C will reduce the risk of cancer. These phytochemicals and nutrients are most readily available in fresh fruits and vegetables."