Vitamin C may reduce effectiveness of anti-cancer drugs
Vitamin C substantially reduces the ability of anti-cancer drugs to kill cancer cells in the laboratory, say scientists in the US.
Researchers at Columbia University and Memorial Sloan-Kettering Cancer Centre in New York treated samples of cancer cells with a wide variety of chemotherapy drugs.
The cells had been pre-treated with dehydroascorbic acid (DHA), the form that ascorbic acid (vitamin C) takes to enter cells, to simulate high-dose vitamin C supplements.
The researchers discovered that in cells which had been pre-treated with vitamin C, none of the anti-cancer drugs - including the targeted agent Gleevec - worked as well as expected.
Of those cells which had been pre-treated with vitamin C, between 30 and 70 per cent fewer were killed by the anti-cancer drugs.
The researchers also repeated their tests on mice which had been implanted with cancer cells. They found that tumours grew more rapidly in mice whose implanted cancer cells had been pre-treated with vitamin C.
Dr Joanna Owens, Cancer Research UK's senior science information officer said: "These are interesting but early results. As yet, there is not enough evidence to know whether antioxidants such as vitamin C are helpful or harmful during cancer treatment.
"It's possible that high doses of antioxidants can make treatment less effective, but until we know for sure our advice is to try and get the vitamins you need through a balanced and varied diet, rather than through vitamin supplements."
The study, which is published in the journal Cancer Research, suggests that vitamin C protects cells from being killed by anti-cancer drugs by protecting their energy-producing mitochondria.
When a cell's mitochondria become damaged, they usually send signals which initiate cell death. Many anti-cancer drugs disrupt mitochondria so that the affected cells die.
Dr Mark Heaney, an associate attending physician at Memorial Sloan-Kettering Cancer Centre, revealed: "Vitamin C appears to protect the mitochondria from extensive damage, thus saving the cell."
The expert also revealed that cancer cells appear to accumulate more vitamin C than normal cells.
He said: "We recognised that DHA is the form of vitamin C that gets into cells, and that the tumour microenvironment allows cancer cells to convert more vitamin C into DHA. Inside the cell, DHA is converted back into ascorbic acid, and it gets trapped there and so is available to safeguard the cell."
However, the researchers emphasised that studies need to be carried out on humans before firm conclusions can be drawn.
Dr Heaney also noted that the levels of vitamin C found in fruits and vegetables should not cause concern and that cancer patients should continue to eat a healthy diet with plenty of vitamin C-rich foods.