Scientists believe that women who are born left-handed may have been exposed to higher levels of sex hormones in the womb.

They are more than twice as likely to be diagnosed with pre-menopausal breast cancer, according to a study published in the online version of the British Medical Journal. Researchers from the University Medical Centre in Utrecht followed more than 12,000 women born between 1932 and 1941.

They took into account other risk factors for breast cancer, such as body weight, smoking habits, family history and socio-economic status. Even when all these were adjusted for, women who were left-handed were 2.41 times more likely to develop breast cancer before the menopause.

The scientists believe the increased risk is linked to exposure to higher levels of oestrogen in the womb. High levels of oestrogen in utero are believed to induce left-handedness, although the reason is unclear.

Liz Carroll, head of services at Breast Cancer Care, said: "It is important to remember that the single biggest risk factor for breast cancer is age - 80 per cent of women diagnosed with this disease are over 50."

Emma Taggart, director of policy at Breakthrough Breast Cancer, said the study did not give enough evidence to link left-handedness with breast cancer.

n Mouth cancer, once associated with older men, is becoming increasingly common in younger people and women. It is thought that binge drinking and smoking may account for the rise.