Antioxidants can cause cancer spread

New research has shown that taking antioxidants vitamin pills after a cancer diagnosis might increase the chances of the disease spreading. Antioxidants, like beta-carotene and vitamin E, were believed to help protect our DNA from damage and reduce the risk of cancer. But clinical trials of antioxidant supplements suggests that, in fact, they might have the opposite effect - and increase the chances of dying from the disease. A new study on mice with the skin cancer melanoma, by Martin Bergo from the University of Gothenburg in Sweden, helps to explain why. Kat Arney finds out more...

Martin - First, we studied what happens when we gave the antioxidants to the mice that already had small tumours on their skin. So, we gave them an antioxidant in the drinking water.  At first, we were surprised because we didn't see any effect on the primary tumour. The number in sizes of primary tumours were unaffected. But then when we looked inside, it turned out that the antioxidant supplementations had doubled their frequency of metastasis.

Kat - So, that's cancer spreading through the body.

Martin - Yes, exactly and that's really the most dangerous part of most cancer's progression and in particular, the cell for malignant melanoma.

Kat - What do you think your results might mean for patients? Obviously, this is an animal study but are there lessons that we can take or is it a bit soon to say?

Martin - I don't think it's too soon to say. The first thing we did after we found this in the mice is that we looked at a large panel of human malignant melanoma cell lines and we found the same thing there, even when they were cultured, that the proliferation of these cells were their ability to divide did not differ when we gave them antioxidants. That's in analogy to the primary tumour not being affected in the mice. But then their ability to migrate and invade tissues was increased by antioxidants. So, this actually happens in human cells also.

Kat - How are the antioxidants having this effect? It seems a bit strange that something like that could be encouraging cells to grow and invade more?

Martin - I think the simplest way to put it is that antioxidants can protect healthy cells from free radicals, but they can also protect tumour cells from free radicals. Free radicals can limit a tumour cell's ability to proliferate and free radicals can limit the ability of malignant melanoma cells to metastasise. So, the antioxidant is helping the tumour cell.

Kat - Is there a message for cancer patients from this research, perhaps if they're seeing adverts for antioxidants or reading about them on the internet?

Martin - This is something that is very important to debate at this point. Research is showing that people who have just been diagnosed with cancer are more prone to take antioxidant supplements than the general population. So this is very important that they find out the potential risks of that. It's time to perhaps draw some general recommendations from that and suggest that cancer patients should not supplement their diet with antioxidants.

Kat - We do hear a lot about naturally occurring antioxidants in fruit and veg, and things like that. Does this mean that people shouldn't eat their "5 a Day", or avoid fruit and vegetables?

Martin - That's a very good question. It is important to note that we have studied antioxidant supplementation and we have chosen doses that you would be expected to get as a human if you were taking a supplement - a pill. But it's not excessive doses. You wouldn't have to take a lot of those pills. You would have to take a normal dose of an antioxidant supplement. So, there is no reason, at least from our studies, to suggest that antioxidants in the food would cause this effect.