British scientists have discovered that breastfeeding for at least six months may help mothers remain slimmer in their 50s, according to a recent study published in the International Journal of Obesity.

Researchers from the University of Oxford have found that the more babies a woman had, the higher her Body Mass Index (BMI) decades later. However, the study also showed that mothers who breastfed had a significantly lower BMI compared to those who did not.

The study states that for every six months of breastfeeding, there is an associated 1% reduction in BMI. Previous studies have shown that only a modest 1% decrease in BMI in western countries could considerably diminish the number of obesity related illnesses and their costs.

‘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’, said Professor Dame Valerie Beral, study co-author and Director of the Cancer Epidemiology Unit at the University of Oxford.

This weight-control benefit of breastfeeding appeared to be independent of risk factors for obesity, such as physical activity, smoking and socioeconomic status.

‘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 has given birth’, said lead author Dr Kirsty Bobrow, from the University of Oxford.

The BMI is an index relating weight to height and is used as a guideline to determine whether an individual is underweight, overweight, obese or has a normal weight. It is calculated by dividing a person’s weight in kilograms by the height in metres, squared. An individual with a BMI between 25 and 30kg/m2 is considered overweight, while one whose BMI is 30kg/m2 or greater is obese.

Study details

The study was supported by Cancer Research UK and the Medical Research Council. It consisted of 740,628 post-menopausal women who had also participated in the Million Women Study. The subjects’ mean age was 57.5 years and they had an average BMI of 26.2kg/m2. Most of these women (88%) had given birth at least once and of these, 70% had breastfed for an average of 7.7 months.

Up to now, only two small studies have investigated the link between BMI or a related measure later in life, and breastfeeding history. The studies’ findings are consistent with this research: among middle-aged Swedish women the incidence of abdominal obesity decreased with their duration of breastfeeding and among Dutch middle-aged women (an atypical population born during the 1944/46 Dutch famine), the BMI of mothers who had breastfed was lower compared to those who had not.

While the exact reason behind this weight-control benefit of breastfeeding was not investigated, it remains that this practice may not only set mothers on a healthier trajectory that is long-lasting but may also reduce their risk of developing breast cancer.


    Bobrow et al (2013) Persistent effects of women's parity and breastfeeding patterns on their body mass index: results from the Million Women Study. Int J Obes (Lond). 37(5):712-7.