Left-handed women are more than twice as likely as right-handers to suffer from breast cancer before reaching menopause, Dutch scientists said.
More than a million women are diagnosed with breast cancer world-wide each year. Three-quarters of cases occur after menopause, which usually begins around the age of 50.
Researchers at the University Medical Centre in Utrecht in the Netherlands speculate that there is a shared origin early in life for both left handedness and developing breast cancer, possibly exposure to hormones in the womb.
"Left handedness is associated with breast cancer, most specifically pre-menopausal breast cancer," said Cuno Uiterwaal, an assistant professor of clinical epidemiology at the university, in an interview.
"We found that left-handed women are more than twice as likely to develop pre-menopausal breast cancer as non-left handed women," the researchers said in the report published online by the British Medical Journal.