Weight gain in middle-aged men, about 2st 7lb from their teenage years to retirement can increase their cancer risk by 50% while in women the risk of cancer rises by almost 20 per cent over a lifetime if they put on 3st 7lb.
In the study of 300,000 people in the US, researchers from Manchester University looked at changes in men and women's body mass index (BMI) between the ages of 18 and 65. By recording those who developed obesity-related cancers, they were able to determine the risk from their weight.
‘Breast and bowel cancer are the two most common obesity-related cancers and pancreatic, oesophageal and gallbladder are the most difficult to treat.’
It is not known exactly why piling on the pounds can lead to the disease, although excess fat is believed to produce hormones which help cancer to develop.
Lead author Dr Hannah Lennon 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."
Being overweight is the second biggest preventable cause of cancer in the UK after smoking and can cause 13 different cancers. Middle-aged men with 'beer bellies' and 'apple-shaped' women are particularly at risk, with too much fat stored around the middle linked to bowel, kidney, oesophageal, pancreatic and breast cancer.
The men in the study at 50 percent greater risk of cancer were not obese, which is classed as a BMI of above 30, but had gone from a BMI of 22 to 27 - within the overweight bracket.
For a man of average weight, this equated to putting on 2st 7lbs over a lifetime. Women who went from a BMI of 23 to 32 had a 17 percent increased risk of cancer in comparison to those whose weight stayed stable and healthy.
Sir Harpal Kumar, chief executive of Cancer Research UK, said, "This is a really interesting way to look at lifetime risk of obesity-related cancers and helps us understand the effects of weight gain over time.
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."
Dr Karen Kennedy, director of the National Cancer Research Institute, 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."