A new study, published in the International Journal of Obesity and funded by Cancer Research and the Medical Research Council (MRC), found that women who breastfed their children have a lower body mass index (BMI) than women who did not.

The research consisted of 740,000 post-menopausal UK women. Scientists found that long-term weight was affected in both childbearing and breastfeeding women, but the effects were significantly different.

The women's BMI increased according to how many children they had. However, those who breastfed had a considerably lower average BMI, no matter how many children they conceived.

Women had a 1 percent decrease in their BMI with every 6 months they breastfed. Other factors that are highly associated with obesity such as smoking, exercise and social deprivation did not have an effect on women's BMI.

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

"Our research suggests that just six months of breastfeeding by UK women could reduce their risk of obesity in later life. A one percent 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, leading author of the paper, explained how this research shows mothers how breastfeeding not only benefits their babies, but also themselves, even 20 years after they give birth. Now that they are aware of these benefits, she wants this information to help pregnant women make an informed decision whether or not to breastfeed.

According to previous studies, women lose weight within months of giving birth with the help of breastfeeding. However, there has not been much research acknowledging the relationship with long-term BMI.

Director of the MRC/Chief Scientist Office Social and Public Health Sciences Unit, Professor Dame Macintyre, 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."

Researchers used participants for their cross-sectional study who were also involved in the Million Women Study, which explores the relationship between numerous reproductive and lifestyle factors and women's health. Questions about the women's weight, height, reproductive history, and other applicable factors were investigated.

The majority of the women in the study (88 percent) had at least one child. 70 percent of these women had breastfed for about 7.7 months on average. The average age was about 57.5 with a mean BMI of 26.2kg/m2.

The authors explain that more research needs to be done to find out if other populations experience the same effect, especially in developing countries where breastfeeding and childbearing are unlike those in the UK.

Written by Sarah Glynn