Adults who gain a considerable amount of weight between their teenage years and retirement can raise their risk of developing cancer by up to 50%.
Experts said the study reiterates why it’s so vital for people to maintain a healthy weight as they age.
“While there are no guarantees against the disease, keeping a healthy weight can help you stack the odds in your favour and has lots of other benefits too,” said Sir Harpal Kumar, Cancer Research UK’s chief executive.
For the study, researchers at The University of Manchester and The Health eResearch Centre looked at the weight gain of 300,000 people over many years and assessed the risk of developing obesity-related cancers.
They categorised the population into five different lifetime weight trajectories and then looked at changes in BMI between the ages of 18 and 65 years old.
Some people gained a little weight between this period, while others became morbidly obese.
Researchers then followed up for an average of 15 years to see who went on to develop obesity-related cancers.
Men who went from a BMI of around 22 to 27 had a 50% increased risk of developing obesity-related cancer compared to a man who stayed within a healthy weight range. This BMI increase is equivalent to an extra 2st 7Ibs increase for the average height man of 177cm.
In men who went from being overweight to morbidly obese, the risk went up by 53% compared to the same group.
Women who went from a BMI of 23 to around 32 had a 17% increased risk in comparison to women whose weight started off in the healthy bracket and remained stable.
Of the 300,000 people in the study, there were around 9,400 women and 5,500 men who were diagnosed with obesity-related cancers after the age of 65.
Being overweight has been linked to bowel, breast and pancreatic cancer. In women, it can also raise the risk of womb and ovarian cancer.
Dr Hannah Lennon, lead author and researcher at The University of Manchester, said: “This research shows how important it is to look at weight gain over a person’s lifetime – to give a clearer picture of cancer risk through life compared to assessing someone’s BMI at a single point.
“This study could also be really useful in public health. It could help identify people who would benefit the most from taking action to control their weight before any health problems arise – including a cancer diagnosis.”
Sir Harpal Kumar, Cancer Research UK’s chief executive, said: “It’s important that people are informed about ways to reduce their risk of cancer. And while there are no guarantees against the disease, keeping a healthy weight can help you stack the odds in your favour and has lots of other benefits too.
“Making small changes in eating, drinking and taking exercise that you can stick with in the long term is a good way to get to a healthy weight – and stay there.”
Dr Karen Kennedy, director of the National Cancer Research Institute (NCRI), said: “This study provides a deeper understanding of the health implications caused by the obesity epidemic.
“It helps paint the picture of how risk could accumulate over time for different people, and could provide health professionals with a means to asses an individual’s risk.”