Women who put on weight from early adulthood are less likely to develop breast cancer before they reach menopause, a landmark international study has found.
Those who gain 22lb between their 20s and early 50s reduce their risk by 8 per cent, compared with women whose weight remained stable, according to scientists.
An analysis of data from more than 620,000 women worldwide revealed a reduction in risk of around 4% for each 11lb gained between ages 18 to 24 and 45 to 54.
The research, led by scientists at the Institute of Cancer Research (ICR) in London, found the likelihood of developing breast cancer fell as long as the weight gain began before the age of 35.
Being heavier as a young adult is known to lower the risk of premenopausal breast cancer, but it has until now been unclear what impact any subsequent weight change might have.
Experts believe that the extra weight gives some women a “protective effect”, which means they are less prone to breast tumours.
Dr Minouk Schoemaker, a senior researcher at the ICR, told The Telegraph: “Women who are heavier in early adulthood tend to have been heavier in early childhood. So, it is possible that early changes that happen to breast composition during property could influence your risk later in life, as heavier girls have more fat tissues compared to breast tissues because they have larger breasts, which seem to be protective.”
Breast cancer is the UK’s most common cancer, with around 55,000 women and 370 men being diagnosed with the disease each year in the UK.
It is hoped the findings, published in the International Journal of Cancer, could help doctors target when individuals may benefit most from breast screening.
A personalised NHS screening programme based on changes in patients’ body mass index (BMI) could also be introduced in the future.