A by-product of cholesterol fuels the growth and spread of breast cancer, research has shown.

Scientists also discovered that cholesterol-lowering statin drugs can reduce its harmful effects.

Modifying diet, or taking statins, to lower cholesterol could provide a straight­forward way to lower breast cancer risk, they believe.

Previous studies had already shown a link between raised cholesterol and breast cancer, but one that could not be explained.

The new American research, conducted on mice, shows for the first time how a breakdown product of cholesterol called 27HC drives breast cancer by mimicking the effects of the hormone oestrogen.

Three quarters of breast cancers are sensitive to oestrogen, which stimulates tumour growth.

Lead scientist Dr Donald McDonnell, of North Carolina, said: "A lot of studies have shown a connection between obesity and breast cancer, and specifically that elevated cholesterol is associated with breast cancer risk, but no mechanism has been identified.

"What we have now found is a molecule - not cholesterol itself, but an abundant metabolite of cholesterol - called 27HC that mimics the hormone oestrogen and can independently drive the growth of breast cancer."