Accounting for close to 10% of all cancer cases, bowel cancer is the third most common cancer worldwide and represents a major cause of sickness and death across the globe. While little is known about the precise cause of this disease, a number of risk factors have been identified over the years, like a diet rich in red meat, smoking, inflammation, alcohol, lack of exercise and a family history of bowel cancer, to name a few.
Now, to add to this list, scientists have found that being obese during your teenage years could double your chances of developing this cancer later in life. But this finding hasn’t exactly come as a total shock: Scientists already knew that this type of cancer was linked with adult obesity, but the research hadn’t been extended to adolescents before.
In order to do so, an international team of researchers from Orebro University Hospital in Sweden and Harvard University enrolled almost quarter of a million young Swedish men into a long-term study aiming to evaluate the associations of adolescent body mass index (BMI) and inflammation with colorectal, or bowel, cancer risk.
At the point of enrollment, which took place over several years, all of the men were between the ages of 16 and 20. A variety of measurements were taken at the start, including weight, height and a measure of inflammation called erythrocyte sedimentation rate (ESR), which revealed that the vast majority were considered of a normal weight. Only 1.5% were classified as very overweight at the start of the study, with a BMI of between 27.5 and 29.9, and 1% were considered obese with BMIs greater than 30.
Using national cancer registry data, the men were then followed for an average of 35 years in order to monitor the incidence of colorectal cancer. As described in the journal Gut, 885 of the men included in the study went on to develop bowel cancer, almost half of which were cases of rectal cancer. But these incidences were not evenly distributed among the different body weight groups: Those falling in the very overweight category during adolescence were twice as likely to develop bowel cancer later on, and those classed as obese had a risk 2.38 times greater than those of normal weight.
By indirectly measuring the degree of inflammation present throughout the body using the ESR test, the researchers also discovered that inflammation above a certain threshold during adolescence significantly raised the risk of developing bowel cancer during adulthood. The inflammatory response is essential to our bodies in that it helps guide tissue repair and defenses to infection, but on the flip side there seems to be a clear link between this response and the onset of cancer. The relationship is complex and not well understood, but scientists think that long-term inflammation could possibly bring about cellular environments that foster DNA damage and thus the formation of tumor cells.
Of course, as with any observational study, it’s not possible to assert that either systemic inflammation or obesity cause bowel cancer, but rather that an association exists. Further studies are therefore warranted to probe this link further, which seems to be justified given the fact that both obesity and bowel cancer are increasing among this age group.
1