Left-handed women may be twice as likely as others to develop breast cancer before the menopause, according to a Dutch study published today.

Researchers at the University Medical Centre, Utrecht, investigated the records of 1,426 women, a random sample from middle-aged women screened for breast cancer, of whom just over one in 10 were left-handed. They suggest, in the journal BMJ Online First, that exposure to high levels of sex hormones before birth, which could induce left-handedness as well as changes in breast tissue, could be responsible.