Differences in lifestyle and reproductive factors are the main reasons behind lower breast cancer rates in South Asian and black women, according to research published in the British Journal of Cancer today (Wednesday).
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 – Dr Toral Gathani, lead author
Breast cancer incidence rates in England are lower in black and South Asian women compared with white women, but the reasons for these differences have not been fully understood – until now.
Data from the Million Women Study* showed that South Asian women had an 18 per cent lower rate of breast cancer compared with white women, and black women had a 15 per cent lower rate of breast cancer compared with white women**.
South Asian and black women drink less alcohol and have more children than white women – and both these factors influence the risk of developing breast cancer. But when these, and other lifestyle and reproductive factors were excluded from the analysis, the risk of developing breast cancer was found to be similar for women of all ethnic groups.
Many of the black and South Asian women in the study were first-generation immigrants. And it is likely that as second and subsequent generations of women of ethnic minority origin change their lifestyles, their risk of breast cancer will increase.
Study author 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 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 per cent of women survive beyond 10 years.
Dr Julie Sharp, Cancer Research UK’s head of health information, 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.”
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Ethnic differences in breast cancer incidence in England are due to difference in known risk factors for the disease: prospective study. BJC. Gathani et al. doi: 10.1038/bjc.2013.632
*The Million Women Study is a national study of women’s health, involving more than one million UK women aged 50 and over. It is a collaborative project between Cancer Research UK and the National Health Service, with additional funding from the Medical Research Council and the Health and Safety Executive, which aims to answer many outstanding questions about the factors affecting women’s health in this age group.
Women were recruited to the Million Women Study in 1996-2001 aged 50-64 at recruitment.
** Comparison is for women of the same age and region of residence. South Asian vs white women, relative risk (RR) of breast cancer = 0.82, 95 per cent CI 0.72–0.94. Black vs white women RR = 0.85, 95 per cent CI 0.73–0.98).
***Factors known to reduce the subsequent risk of breast cancer include starting periods later, giving birth a greater number of times, greater 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 menopausal hormone therapy, and a family history of the disease.