The waistlines of more than half of women are too big, experts have said, as they warned those who are overweight they are increasing their risk of cancer and infertility.
Researchers found that the average waist measurement for women is 4.9cm larger than the healthy size of less than 80cm.
Larger waists could lead to an increased chance of fertility problems, cancers, type 2 diabetes and heart disease.
Research by the health charity Nuffield Health examined data from more than 30,000 women and found that 57% have a waist larger than the healthy size.
It said women in the north of England have the largest waists, with an average circumference of 87cm. In London the average size is 81.9cm.
Researchers also said that 52.5% of the women have a body mass index in excess of the healthy range, while 16.2% have scores which found they were moderately or morbidly obese.
Dr Davina Deniszczyc, professional head of physicians and diagnostics at Nuffield Health, said: "Whilst waist size may seem like a cosmetic issue, this isn't about women fitting into their skinny jeans. Rather, it's an important indicator of overall health and well-being, particularly when taken into account with other health measurements.
"The results for women highlight a worrying problem as fat being stored around the waist can contribute to significant health issues, such as breast cancer and infertility."