Women who go up a skirt size over a decade between their mid-20s and mid-60s increase their chances of developing breast cancer by a third, research suggests.
A study found expanding waistlines in women were linked to a 33 per cent greater risk of developing breast cancer after the menopause, while going up two sizes increased the chances by 77 per cent.
The researchers, writing in the British Medical Journal Open, said that while overall weight gain during adulthood was a known risk factor for breast cancer, a thickening waist seems to be particularly harmful, indicating the importance of staving off a midriff bulge.
More than 4,500 cases of breast cancer are diagnosed in Scotland each year, with more than 1,000 deaths annually. At least one in four women in the country is also considered obese.
The latest findings, by researchers from University College London (UCL), were based on almost 93,000 women taking part in the UK Collaborative Trial of Ovarian Cancer Screening.
The women were all aged over 50, had gone through the menopause, and had no known breast cancer when they entered the study between 2005 and 2010.
The participants provided detailed information on height and weight, reproductive health, fertility, family history of breast and ovarian cancer, and use of hormonal contraceptives and hormone replacement therapy (HRT) – all of which can influence breast cancer risk.
The women were asked about their current skirt size, and what this had been in their 20s.
After three to four years, the participants were again asked about their continued use of HRT, their general health, any cancer diagnosis and lifestyle, including how much they smoked and drank.
The researchers discovered that 1,090 women developed breast cancer, giving an absolute risk of just over 1 per cent of the total number examined.
As had been expected, infertility treatment, family history of breast or ovarian cancer and use of HRT were all significantly linked to a heightened risk of breast cancer, while having had a baby gave some protection against the disease.
After taking account of other factors, increases in skirt size emerged as the strongest predictor of breast cancer risk. At the age of 25, the women’s average skirt size had been a UK 12, and when they entered the study at the average age of 64, it was a 14.
The team said as it was an observational study, no definitive conclusions could be drawn about cause and effect.
They said: “Although the exact mechanism of these relationships needs to be better understood, there is a suggestion that body fat around the waist is more metabolically active than adipose [fatty] tissue elsewhere.”
James Jopling, director for Scotland at Breakthrough Breast Cancer, said: “We know that 40 per cent of breast cancers could be prevented by changes to lifestyle such as being regularly active and maintaining a healthy weight.
“This study highlights an easy way to monitor your weight gain over time. Women are more likely to remember their skirt size when they were younger than their body mass index.”