White women are more likely to develop cancer than their South Asian and black counterparts because of “lifestyle and reproductive factors”, a new study suggests.
Compared with women from these ethnic backgrounds, white women in England have higher breast cancer rates, researchers said.
But when taking into account risk factors such as breastfeeding rates and the number of children women had, the risk of developing breast cancer was found to be similar for women of all ethnic groups.
Researchers from the University of Oxford and Oxford University Trust examined data from more than 1,000,000 women in England who participated in the Million Women study.
Women aged 50 to 64 were enrolled into the study, designed to investigate links between health and lifestyle, from 1996 to 2001. Participants completed questionnaires about living habits, medical and social factors and cancer data was obtained from NHS cancer registries.
The authors found that after around 12 years, 217 of 5,877 South Asian women developed breast cancer, as did 180 of 4,919 black women and 45,191 of 1,038,144 white women - meaning South Asian women had an 18% lower rate of breast cancer compared with white women, and black women had a 15% lower rate compared to white women.
The study, published in the British Journal of Cancer, also found numerous differences in known risk factors such as alcohol consumption and use of menopausal hormone therapy, among others.
For instance South Asian and black women had more children than white women and were more likely to breastfeed them - 69% of white women said they had breastfed their children compared to 83% of black women and 85% of South Asian women.
Meanwhile, 75% of South Asian women said they were non-drinkers compared to 38% of black women and 23% of white women.
And 35% of white women said they were a current user of menopausal hormone therapy compared to 22% of South Asian women and 29% of black women.
Women from black and South Asian backgrounds were also less likely to have a first degree relative with breast cancer.
After the researchers excluded these, and other lifestyle and reproductive factors, from the analysis the risk of developing breast cancer was found to be similar for women of all ethnic groups.
They concluded that the differences “largely, if not wholly” account for the different rates of breast cancer among women from different ethnicities.
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