In England, black and South Asian women have lower rates of breast cancer than white women. Now, a new study from Oxford University suggests the reason lies with differences in lifestyle and reproductive patterns.
The team, from Oxford's Cancer Epidemiology Unit, lists alcohol consumption, breastfeeding and number of children as some of the factors.
The data for the study, which is published in the British Journal of Cancer came from the Million Women Study, which is run by Oxford University and whose participants comprise women aged 50 and over living in the UK.
The data shows in England, South Asian women have an 18% lower rate of breast cancer, and black women have a 15% lower rate, than white women.
But the researchers found these differences in risk disappeared when they took into account the effect of lifestyle and reproductive factors.
Lead author Dr. Toral Gathani, a clinical epidemiologist and consultant surgeon, says:
"In this study of largely postmenopausal women in England, we see that the lower risk of breast cancer in South Asian and black women is largely explained by differences in lifestyle and reproductive patterns."
White women drink more, have fewer children, and are less likely to breastfeed
White women are less likely to breastfeed, have fewer children, and are more likely to drink alcohol than South Asian and black counterparts. They are also more likely to have a first-degree relative - such as a sister - with breast cancer, a factor known to raise the risk of the disease.
New research finds that white women in England are more likely to develop breast cancer than black or South Asian women because of their lifestyle and reproductive patterns.
The researchers note that the black and South Asian women in the study are first generation immigrants to the UK and suggest it is likely that the breast cancer risk of their children and grandchildren will go up as their lifestyles become more westernized.
Dr Gathani says:
"It's important for women of all ethnic groups to understand what are the modifiable risk factors for breast cancer, such as obesity and excessive alcohol consumption, and to take measures to reduce their risk."
In the United States, where next to skin cancers, breast cancer is the most common cancer among American women, the American Cancer Society estimates that 1 in 8 women will develop invasive breast cancer in their lifetime.
In the UK, breast cancer is the most common cancer. And while more people are being diagnosed with the disease, survival rates are improving. Today, 80% of women survive more than 10 years after diagnosis.
Research shows that the risk of breast cancer increases with a family history of the disease, alcohol consumption, and use of hormone therapy, and it is lower in women who start periods later, give birth a greater number of times, breastfeed for longer, have a lower body mass index, and who are not tall.
Women can reduce risk of breast cancer with lifestyle changes
Dr. Julie Sharp, head of health information at Cancer Research UK, who co-sponsor the Million Women Study, says:
"Women can reduce their risk of breast cancer by cutting down on alcohol, keeping a healthy weight by eating a balanced diet and by keeping active."
She says they should also tell their doctor straight away if they notice any changes in their breasts, such as skin or nipple changes, lumps, or changes to size, shape or feel, and adds:
"It's probably not cancer, but if it is, getting it diagnosed as early as possible gives the best chance of survival."
Meanwhile another huge study of women based in the US finds that diet and exercise are linked to a 20% lower risk of cancer death.