Women with a family history of breast cancer should be "strongly encouraged" to breastfeed, an expert said today, after research shows it can cut the cancer risk.

US-based researchers reviewed the cases of more than 60,000 women who gave birth and who also took part in a major health survey from 1997 to 2005. Just over 600 cases of premenopausal breast cancer were detected in the group of women, with the illness hitting them at an average age of 46.2 years.

When the women had someone in their close family with breast cancer, they were found to have a lower risk of developing the disease if they had ever breastfed than if they had never breastfed.

The study also found women who did not breastfeed but used medication to suppress their breast milk production could also lower their hereditary risk of breast cancer.

Dr Alison Stuebe, of the University of North Carolina, said the beneficial effect from breastfeeding was similar to "high risk" women undertaking hormone-based treatments to reduce their cancer risk.

"Moreover, breastfeeding is associated with multiple other health benefits for mother and child," Dr Stuebe said. "This data suggests that women with a family history of breast cancer should be strongly encouraged to breastfeed."

The research is published in the journal Archives of Internal Medicine.

Women who carry the genes BRCA1 and BRCA2 are known to have an increased lifetime risk of developing breast cancer.

Australia's Dr Judy Kirk, a spokeswoman for the National Breast Cancer Foundation, said childbirth was known to offer a protective effect against breast cancer for these women.

"There is less research about the effect of breastfeeding in those very high risk women," Dr Kirk said. "So, in a way, it is not surprising this study has also shown a reduction of risk of breast cancer for premenopausal women ... from breastfeeding."