Concern over vitamin C supplements for cancer patients

Wednesday October 1st, 2008

Vitamin C supplements may interfere with chemotherapy drugs, researchers warned today.

Dr Mark Heaney and colleagues at Memorial Sloan-Kettering Cancer Center, New York, USA, investigated the effects of vitamin C supplements in laboratory tests and using mice.

They report in the journal Cancer Research that vitamin C substantially reduces the effectiveness of anticancer drugs. The same mechanism may apply to humans and affect patient outcomes.

Previous studies have suggested that vitamin C's antioxidant effects might benefit cancer patients. However, the "free radicals" triggered by some chemotherapy drugs may be halted by vitamin C, preventing them from killing cancer cells.

The researchers tested several chemotherapy drugs, including some that produce these free radicals, on cancer cells in the lab. Some cancer cells were pre-treated with dehydroascorbic acid (DHA) - the form that vitamin C takes when it enters the body's cells.

Surprisingly, every chemotherapy drug tested was less effective on cancer cells that were given vitamin C. Depending on the drug, effectiveness was reduced by 30 to 70 per cent.

The same result was found when cancer cells were implanted into mice. The animals' tumours grew faster when they were given vitamin C.

But the reason may not be linked to free radicals, say the experts. Instead, it might be that DHA restores viability to a part of the cancer cells called their mitochondria.

Dr Heaney said: "Vitamin C appears to protect the mitochondria from extensive damage, thus saving the cell. And whether directly or not, all anticancer drugs work to disrupt the mitochondria to push cell death."

But he added that further work must be done before a firm conclusion is reached.

Heaney, M. et al. Cancer Research, Vol. 68, October 1 2008.

Tags: Cancer

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