Scientists claim high levels of iron may be one reason why eating red meat raises the risk of bowel cancer.

Iron may switch on the disease process via a faulty gene in the gut which would normally resist the disease.

Red meat contains large amounts of iron and is also known to increase the likelihood of bowel cancer.

The discovery could lead to new treatments that can 'mop up' iron in the bowel in people who develop cells affected by the defective gene.

In studies of mice, researchers found that susceptibility to bowel cancer was strongly influenced both by iron and a gene called APC.

When the APC gene was faulty, mice with a high iron intake were two to three times more likely to develop the disease.

Mice fed a low iron diet remained cancer free even if the gene was defective, but when it functioned normally, high iron levels did no harm.

Lead scientist Professor Owen Sansom, deputy director of the Cancer Research UK Institute in Glasgow, said 'We've made a huge step in understanding how bowel cancer develops.

'The APC gene is faulty in around eight out of 10 bowel cancers but until now we haven't known how this causes the disease.

'It's clear that iron is playing a critical role in controlling the development of bowel cancer in people with a faulty APC gene.

'And, intriguingly, our study shows that even very high levels of iron in the diet don't cause cancer by itself, but rely on the APC gene.'

Each year, more than 41,000 people in the UK are diagnosed with bowel cancer and around 16,000 die from the disease.

Previously, researchers have estimated that red meat contributes to around 17,000 cases of bowel cancer a year.

But this estimate was based on two different dietary factors thought to play a part in promoting bowel cancer because a substance called haem, which gives red meat its colour, can damage the lining of the colon, while burning meat produces cancer-causing compounds.

The latest laboratory study proposes another mechanism that, if confirmed in people, might help explain why people's risk of bowel cancer increases with age.

Over time, cells in the bowel would be increasingly likely to develop APC gene faults and thus react to iron in the diet.

Researchers say that when the APC gene doesn't work, iron is allowed to build up in the cells lining the gut.

This activates a genetic cancer 'switch' called wnt that causes cells to multiply out of control.

But consumption of iron also aids the growth of cells with defective APC over time, says the study published in the journal Cell reports.

In mice fed a diet with no iron, cells with a faulty APC gene were killed off and bowel cancer did not develop.

Mice with a fully functioning APC gene did not grow tumours even when fed high amounts of iron in their diet. In these animals, the wnt signalling pathway remained switched 'off'.

Co-author Dr Chris Tselepis, a Cancer Research UK scientist at the University of Birmingham, said 'Our results also suggest that iron could be raising the risk of bowel cancer by increasing the number of cells in the bowel with APC faults.

'The more of these cells in the bowel, the greater the chance that one of these will become a starting point for cancer.

'We're now planning to develop treatments that reduce the amount of iron in the bowel and so could lower the risk of developing bowel cancer.

'We hope to start using these in trials in the next few years in people who are at a greater risk.'

Dr Julie Sharp, senior science information manager at Cancer Research UK, said 'Bowel cancer is the third most common cancer in the UK.

'These findings suggest a potentially effective way of reducing the chances of bowel cancer developing in people who are at high risk.

'Finding ways of 'mopping up' the iron that is in the bowel could have a real impact on the number of people who develop the disease.'