Lifestyle differences and reproductive patterns explain variations in breast cancer rates between ethnic populations in England. South Asian and black women, who have lower rates of breast cancer, are also more likely to breastfeed and less likely to drink alcohol.
Lower rates of breast cancer in South Asian and black women in England are largely explained by differences in lifestyle and reproductive patterns, such as alcohol consumption, breastfeeding and number of children, Oxford University researchers have found.
Breast cancer incidence rates in England are known to be lower in black and South Asian women than in white women, but the reasons for the difference have not been fully understood.
The team from the Cancer Epidemiology Unit at Oxford University used data from the Million Women Study to show that South Asian women had an 18% lower rate of breast cancer incidence compared with white women. Black women had a 15% lower rate of breast cancer incidence.
However, when differences in the lifestyle and reproductive patterns were taken into account, the risk of developing breast cancer was similar for women of all ethnic groups.
South Asian and black women in the study had more children than white women, were more likely to breastfeed them, and were less likely to drink alcohol and to have a first-degree relative with breast cancer.
Many of the black and South Asian women in the study were first-generation immigrants to the UK. The researchers suggest that, as subsequent generations change their lifestyles, it is likely their risk of breast cancer will increase.
Dr Toral Gathani from the University of Oxford said: '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.
'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.'
The research is published in the British Journal of Cancer.
The Million Women Study, funded by Cancer Research UK and the Medical Research Council, is following the health of than one million white women, almost 6,000 south Asian women and almost 5,000 black women in England. Women were recruited between 1996 and 2001, when they were aged 50-64 years, and filled in questionnaires asking about their lifestyle and other risk factors. Information on breast cancer was obtained from National Health Service cancer registries.
Breast cancer is the most common cancer in the UK. More than 49,500 UK women are diagnosed with the disease and around 11,600 women die from breast cancer each year. But survival rates have been improving dramatically over time and now nearly 80% of women survive beyond 10 years.
Cancer Research UK's head of health information Dr Julie Sharp said: '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.
'If women notice any changes to their breast such as lumps, any skin or nipple changes, or changes in their size, shape or feel they should tell their doctor straightaway. It's probably not cancer, but if it is, getting it diagnosed as early as possible gives the best chance of survival.'
Factors known to reduce the subsequent risk of breast cancer include starting periods later, giving birth a greater number of times, longer duration of breastfeeding, shorter stature and lower body mass index.
Factors known to increase the risk of breast cancer include greater alcohol consumption, use of hormone therapy, and a family history of the disease.