Overweight women could slash their risk of breast cancer by nearly a third by shedding some pounds, research suggests.
Scientists from the American Cancer Society looked at more than 180,000 women aged 50 or over.
Among those that needed to lose weight, shedding at least 19.8lbs (9kg) - and keeping it off - reduced the risk of developing the disease over the next nine years by 32%.
Even losing 4.6-to-9.9lbs (2.1-to-4.5kg) dashed the odds by 19%, the results show.
“Our results suggest even a modest amount of sustained weight loss is associated with lower breast cancer risk for women over 50,” lead author Dr Lauren Teras said.
One in eight women in the UK and US will develop breast cancer at some point in their lives, statistics show.
Being overweight or obese is “clearly linked” with the disease, as well as tumours of the colon, rectum, womb lining, oesophagus, kidneys and pancreas, according to the American Cancer Society.
This is concerning given that 58% of women in England alone were overweight or obese in 2015, NHS Digital statistics show.
The scientists felt most studies investigating weight and breast cancer were in younger women.
“Studies of weight loss from early to middle-to-later adulthood have mostly been null,” Dr Teras said.
They therefore analysed the risk among middle-aged participants of the Pooling Project of Prospective Studies of Diet and Cancer.
Three surveys over the nine years determined any changes to the women’s weight.
“Sustained weight loss” was defined as shedding at least 4.4lbs (2kg) in the first five years, which was not regained in the following four years.
Results - published in the Journal of the National Cancer Institute - reveal that compared to those with a “stable weight”, the women who lost between 10.1lbs (4.6kg) and 19.6lbs (8.9kg) were 25% less likely to develop breast cancer.
“These findings may be a strong motivator for the two-thirds of American women who are overweight to lose some of that weight,” Dr Teras said.
“It is not too late to lower your risk of breast cancer if you have gained weight after age 50.
“Prevention of the most common cancer worldwide may be a particularly motivating factor for the near epidemic numbers of overweight women.”
Even gaining back some of the weight they lost still left the women less at risk than they were to start off with.
“Women who regained some of the weight after losing 19.8lbs (9kg) were still at a lower risk of breast cancer than women with stable weight,” Dr Teras said.
The overall results were specific to women not on hormone replacement therapy (HRT).
This aims to prevent unpleasant menopausal symptoms by replacing levels of the naturally-declining hormones oestrogen and progesterone.
If HRT is taken for five years, up to one “extra” case of breast cancer could develop in every 50 women on the therapy, the NHS reports.
Exactly why this occurs is unclear. Higher levels of oestrogen may help some tumours grow, according to Breast Cancer Now.