Left-handedness may be set by hormones in the womb

A Dutch team found left-handed women were more than twice as likely to develop premenopausal breast cancer as non-left handed women.

The researchers believe the key may be that left-handers are exposed to greater levels of sex hormones testosterone in the womb.

The study is published online by the British Medical Journal.

Breast cancer is an extremely complex disease and very little is known about the causes Emma Taggart

The researchers, from the University Medical Center Utrecht, examined over 12,000 middle aged women born between 1932 and 1941.

Previous research has suggested that exposure to high levels of sex hormones before birth may induce left-handedness.

It is also thought that the hormones can trigger changes in the breast tissue that make tumour growth more likely in later life.

No reason to worry

Emma Taggart, of the charity Breakthrough Breast Cancer, said: "Women who are left-handed should not worry about these findings.

"Although this is an intriguing study, it doesn't give us enough evidence to link left-handedness with breast cancer.

"Breast cancer is an extremely complex disease and very little is known about the causes.

"The answer is likely to be a complex interplay of factors."

Ms Taggart said women could minimise their risk by eating a balanced diet, drinking less alcohol and exercising regularly.

"It's also vital for women to be breast aware and visit their GP if they are concerned about changes in their breasts."

Lesley Walker, of Cancer Research UK, said the study was based on a relatively small sample.

"A much bigger study is required to determine the actual risks of left handedness.

"If the results of this study are borne out, it could highlight a group of pre-menopausal women to whom early screening could be targeted.

"We know that the strongest risk factor for breast cancer is age. Eighty per cent of breast cancers occur in women over the age of fifty."