Putting on weight could lead to an 11 per cent higher risk of certain cancers, including bowel, breast and pancreatic cancer.
Being overweight or obese is known to raise the risk of at least 13 types of cancer.
But experts have been less clear on whether it is people’s weight that is the major problem, or their obesity-related illnesses including cardiovascular disease and type 2 diabetes.
Now a study of almost 600,000 people has found every five-point increase in body mass index (BMI) is linked to an 11 per cent higher risk of obesity-related cancer, even in people without cardiovascular disease or type 2 diabetes.
This casts doubt on the theory that you can be ‘fat but fit’ – carrying extra weight, without heart problems or diabetes, with little impact on your risk of illness.
A study of almost 600,000 people has found every five-point increase in body mass index (BMI) is linked to an 11 per cent higher risk of obesity-related cancer
A sub-group of 344,000 people from the UK, included in the study, were found to have a 23 per cent higher risk of obesity-related cancers if they were overweight or obese, compared to a normal weight, even when they did not have cardiovascular disease.
Carrying too much weight can cause inflammation in the body, or an excess of the hormone insulin, which may help tumours to grow.
Dr Heinz Freisling, senior author of the study from the International Agency for Research on Cancer, said: ‘We have often talked about people who are overweight but metabolically healthy, meaning they don’t have type 2 diabetes or cardiovascular disease.
‘But this study shows these people still have a higher risk of cancer, so may want to maintain a healthy weight.
‘However their risk goes higher if they also have cardiovascular disease.’
The study, published in the journal BMC Medicine, focused on 13 obesity-related cancers.
These included breast cancer in post-menopausal women only, ovarian and womb cancer, which can be fuelled by hormones produced by fat in the body when people are overweight.
The cancers also included bowel, pancreatic, kidney and gullet cancer.
The risk of getting these obesity-related cancers was 11 per cent higher for every five-point increase in BMI, but 17 per cent higher in people with cardiovascular disease.
This was worked out by looking at the BMI of 577,343 middle-aged people in the UK and Europe, whose BMI was measured, before they were followed up for an average of almost 11 years to see if they got cancer.
The results suggest anyone who is overweight may need to consider their cancer risk, but that people with cardiovascular disease may need to be particularly careful when it comes to their weight.
In the study, someone with cardiovascular disease was defined as anyone who had suffered a heart attack, a stroke caused by loss of blood flow, who had heart failure or coronary heart disease, or irregular heartbeat.
If these people were also overweight or obese, with a BMI over 25, they had 3.4 times the risk of developing obesity-related cancer.
That was compared to someone of a normal weight without cardiovascular disease.
But that result was based only on a group of people from the UK Biobank health study who were analysed by the researchers.
A second group of people, from the EPIC cancer study involving several European countries including the UK, did not produce the same finding.
The researchers reassure people that being overweight or obese, even with cardiovascular disease, is linked to only 50 extra cases of cancer in every 100,000 people per year.
But, although obesity-related cancers make up less than half of total cancers, they include types like bowel and breast which are very common.
As a result, being overweight or obese, with cardiovascular disease, was found to raise the risk of being diagnosed with any type of cancer by 68 per cent, compared to being a normal weight without cardiovascular disease.
Dr Helen Croker, assistant director of research and policy at World Cancer Research Fund, which funded the study, said: ‘We already know that obesity is an important risk factor for cancer, but these striking findings show that the risk differs depending on whether people also have cardiovascular disease.
‘Therefore, maintaining a healthy weight can offer even greater benefits for particular groups.’
