However the study found no link between breastfeeding and reduced risk fo cancer in those women without a history of breast cancer in their family.  The study published in the Archives of Internal Medicine used information from over 60,000 nurses who had given birth and had completed detailed questionnaires about their health with follow-ups every two years.  Around 44,000 women are diagnosed with breast cancer each year in Britain.

Dr Alison Stuebe, then of Brigham and Women's Hospital and Harvard Medical School, Boston, and now of the University of North Carolina found that for women at high risk of developing breast cancer, breastfeeding lowered that risk by as much as taking anti-cancer drug Tamoxifen as a preventive treatment.

Of the 60,000 women in the study, 608 developed pre-menopausal breast cancer by June 2005.  The study found women whose sister or mother had had breast cancer lowered their own chances of the disease by breastfeeding by 60 per cent The link was not affected by whether how long women breastfed for, whether they fed their baby exclusively on breast milk.

Contrary to previous findings there was no link between breastfeeding and breast cancer in women who did not have a family history of the disease.  Dr Stuebe said: "These data suggest that women with a family history of breast cancer should be strongly encouraged to breastfeed."