A study of 740,000 post-menopausal UK women, published in the International Journal of Obesity, found that both childbearing and breastfeeding had significant, but opposite, effects on long-term weight.
The more children a woman had, the higher her BMI decades later. However, the average BMI was significantly lower in women who breastfed than in those who had not, regardless of how many children they had.
For every six months women had breastfed, their BMI was 1 per cent lower, even after accounting for other factors known to affect to obesity such as smoking, exercise and social deprivation.
Professor Dame Valerie Beral, Director of the Cancer Epidemiology Unit at the University of Oxford and study co-author, said:
“Our research suggests that just six months of breastfeeding by UK women could reduce their risk of obesity in later life. A one per cent reduction in BMI may seem small, but spread across the population of the UK that could mean about 10,000 fewer premature deaths per decade from obesity-related conditions, such as diabetes, heart disease and some cancers.”
Dr Kirsty Bobrow, also from the University of Oxford and lead author of the paper, said:
“We already know breastfeeding is best for babies, and this study adds to a growing body of evidence that the benefits extend to the mother as well – even 30 years after she’s given birth. Pregnant women should be made aware of these benefits to help them make an informed choice about infant feeding.”
Sara Hiom, Director of Information at Cancer Research UK, said:
“We already know that breastfeeding can reduce a woman’s risk of developing breast cancer. And this study highlights that breastfeeding may also be linked to weight. Weight in turn influences the likelihood of developing some cancers as well as other diseases. Too few people know about the significant cancer risks associated with being very overweight.”
Professor Dame Sally Macintyre, Director of the MRC/Chief Scientist Office Social and Public Health Sciences Unit, said:
“The obesity epidemic is one of the biggest challenges facing both high income and, increasingly, low and middle income countries. Rates of obesity are continuing to rise. Studies such as this one, which look at broad trends within a large population, can help us to develop effective strategies to prevent obesity and its related diseases.”
Previous research has shown that breastfeeding can help women lose weight accumulated during pregnancy in the months immediately after birth, but fewer studies have addressed the relationship with long-term BMI.
The researchers carried out a cross-sectional study of women who were participants in the Million Women Study, which investigates how various reproductive and lifestyle factors affect women’s health. Women were asked about their height, weight, reproductive history and other relevant factors.
The average age of the women in the study was 57.5 and the mean BMI was 26.2 kg/m2. Most of the women had had at least one child (88 per cent) and of these 70 per cent had breastfed, on average for 7.7 months.
More research is needed to find out whether this effect is observed in other populations – particularly in developing countries where childbearing and breastfeeding patterns are very different to those in the UK.
Notes to editors
For more information or to speak to Prof Valerie Beral, please contact:
Senior Press Officer, Medical Research Council
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1. The paper: ‘Persistent effects of women’s parity and breastfeeding histories on their body mass index: results from the Million Women Study’, by Bobrow et al, is published in the International Journal of Obesity, (2012).
2. The Million Women Study, funded by Cancer Research UK and the Medical Research Council, is a prospective study of 1.3 million women aged between 50 and 64 years when they were invited for screening by the NHS Breast Screening Programme in England and Scotland between 1996 and 2001.
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