New research indicates that women who gain weight and become mothers at an older age might face a considerably higher risk of developing breast cancer.

Experts in the United Kingdom discovered that a big weight gain after the age of 20, plus having a first child after 30 or not having children at all, meant women were almost three times more likely to develop breast cancer than those who gave birth earlier and whose weight remained stable.

The research, which has not yet been published in a peer-reviewed journal, was presented at the European Congress on Obesity in Malaga.

Lead researcher Lee Malcomson, from the University of Manchester, said more women in the UK are now overweight or obese than around a decade ago, while giving birth later in life has been steadily increasing over the past 50 years.

At the same time, diagnoses of breast cancer in women are at their highest ever rate, he said.

He stated, “Additional data regarding how the timing of motherhood and weight gain influences the likelihood of developing breast cancer could help us more accurately determine who is at highest risk for this illness and tailor preventive lifestyle recommendations appropriately.”

In the study, Malcomson and her team examined information from 48,417 women generally aged 57 with a body mass index within the overweight category, approximately 26.3.

The groupings for the women were based on whether they experienced their initial pregnancy before turning 30 years old, after reaching 30 years old, or never having given birth at all. Additionally, adult weight gain was examined across these categories.

Weight gain was calculated by asking women to recall their weight at the age of 20 and subtracting it from their current weight.

The women were followed up for an average of 6.4 years, during which 1,702 were diagnosed with breast cancer.

The findings indicated that women who experienced their first pregnancy at an earlier age tended to have increased weight gain throughout adulthood compared to those whose initial pregnancies happened later. Specifically, for each year sooner the pregnancy took place, these women gained about 0.21 kg more weight.

An early first pregnancy also seemed to protect against post-menopausal breast cancer, which confirms previous research, while weight gain pushed up the risks, which has also been found before.

However, the study found no evidence that having a first pregnancy at an early age managed to offset the increased risk of breast cancer caused by weight gain.

Overall, women who had over a 30% increase in weight during adulthood and either had their first child after age 30, or did not have children, were nearly three times more likely (2.73 times) to develop breast cancer compared with women who had an early first pregnancy and less than a 5% increase in adult weight.

Malcomson stated, “This research is pioneering as it illustrates the way in which weight gain and the age at first childbirth jointly influence a woman’s likelihood of developing breast cancer.”

“It is vital that GPs are aware that the combination of gaining a significant amount of weight and having a late first birth – or, indeed, not having children – greatly increases a woman’s risk of the disease.”