Putting on weight can increase women's risk of ovarian cancer, researchers have found.
Ovarian cancer has a poor prognosis because it has few symptoms and usually is caught at a late stage. If it is caught early more than 90 per cent of women will survive for at least five years, but at the late stage that drops to less than 10 per cent.
The World Cancer Research Fund (WCRF), which works on the prevention of cancer, has published an update of the risks for ovarian cancer. For the first time, it says that overweight and obesity are a probable cause.
Weight is known to be an issue in some other cancers, including breast and bowel cancer.
The WCRF says that maintaining a healthy weight is one of its 10 recommendations for avoiding cancer.
"We can now say with certainty that being overweight or obese increases the risk of developing ovarian cancer, just as it does with a number of other cancers such as breast, bowel and womb cancer," said Dr Rachel Thompson. "This means that women can make lifestyle changes to reduce their chances of getting ovarian cancer.
"Previously we only knew about risk factors that are fixed, such as age and family history of the disease, but now we can say that keeping to a healthy weight helps reduce the risk of getting ovarian cancer."
The increased risk is fairly small.
The British charity Target Ovarian Cancer highlighted the benefits of healthier lifestyles.
"This new study supports earlier work that a healthy lifestyle can reduce your risk of ovarian cancer," said Dr Simon Newman, head of research. "For someone without a family history of ovarian cancer, their lifetime risk of developing the disease is 2 per cent. The findings of this latest study suggest this increases to 2.24 per cent for an obese person, which is still a low risk."