According to British scientists, the role of common genetic differences is limited in causing breast cancer, working independently of more important lifestyle factors like weight, diet and breastfeeding.

Researchers in their study of over 17,000 women participants found, though certain common gene variants increase the risk of breast cancer development, they add rather than multiply the risks lifestyle factors like obesity or drinking pose.

Breast cancer genes known as BRCA-1 and BRCA-2 were not included, and which though occurring rarely confer a high risk on women who have them.

Ruth Travis of Oxford University's cancer epidemiology unit found it reassuring, as whatever common gene variants one inherited, one could reduce the risk of breast cancer by keeping a healthy weight, limiting one's intake of alcohol, including being careful about HRT.

The most common cancer type in wealthy nations, breast cancer kills around half a million people worldwide each year.

Adding to 13 other common genetic risk variants, British scientists found five common genetic factors linked to the risk of developing breast cancer, which combined explain the 8% risk of getting the disease.

Over 7,160 women with breast cancer and 10,196 women without were studied, including the women giving blood samples for genetic testing, as well as, information about their lifestyles.

The researchers looked at 12 genetic variants known as single nucleotide polymorphisms (SNP) for the risk of breast cancer in the DNA of the women, relating these to ten known environmental breast cancer risk factors, namely puberty onset, number of births, age at first birth, breastfeeding, menopausal status, age at menopause, use of hormone replacement therapy (HRT), weight, height, and alcohol consumption.

Publishing their study in The Lancet medical journal, they write none of the 120 comparisons yielded significant evidence of gene-environment interactions, with genes accounting for only a small proportion of breast cancers. Rather, the main risk factors remain lifestyle factors like childbearing, obesity, alcohol consumption and use of HRT.

This is good news as it means women can alter their risk of breast cancer by changing their behaviour.