Colorectal cancer risk increases with every year of overweight

Numerous types of cancer occur more frequently in overweight people than in people of normal weight. These include breast cancer, cancer of the uterus, kidney or esophagus - and also colorectal cancer. This has now been confirmed by numerous studies.

But in most of these studies, the body weight of the participants was only determined once. "Our consideration, however, was that it should play an even greater role in the risk of colorectal cancer how long a person carries around the excess kilos," explains Hermann Brenner, an epidemiologist at the German Cancer Research Center. Scientists assume that obesity is a driver of colorectal cancer because fatty tissue constantly releases growth factors, hormones or pro-inflammatory substances. So it must make a difference whether the body is exposed to this influence only over a comparatively short period of time or whether the obesity persists for decades, possibly even since adolescence.

To test this hypothesis, Brenner and colleagues used data from the DACHS study*. Since 2003, DKFZ researchers have followed and interviewed colorectal cancer patients and randomly selected control participants without a colorectal cancer diagnosis for this case-control study in the Rhine-Neckar region.

The DACHS participants were asked about their weight at different ages since the age of 20. Using this information, DKFZ epidemiologists calculated the number of years of life with obesity** for each of the 5635 patients and 4515 control participants recruited into the study between 2003 and 2017. In addition, the researchers also considered the extent of excess pounds.

The result: compared with permanently normal-weight participants, overweight people have a higher risk of developing colorectal cancer. And this risk increases with the number of overweight years of life and the extent of the excess weight: those participants who had been carrying around many pounds over the long term were two and a half times more likely to develop colorectal cancer than those with a permanently normal weight. Thus, this value has a higher predictive power and correlates much better with the actual risk of colorectal cancer than a one-time determination of overweight.

"It is clear from our study that obesity has an even greater impact on colorectal cancer risk than previously thought. It can be assumed that this is also true for many other diseases for which obesity is a known risk factor. This underlines once again how important it is to prevent obesity from occurring in childhood and adolescence," Brenner emphasizes.

Scientists also apply the concept of "cumulative lifetime exposure" when assessing other primary cancer risk factors. For example, to determine the harmful influence of tobacco, they determine the lifetime "package-years" of smoking as a metric.

Xiangwei Li, Lisa Jansen, Jenny Chang-Claude, Michael Hoffmeister, Hermann Brenner: Risk of Colorectal Cancer According to Lifetime Excess Weight. Jama Oncology 2022, DOI: 10.1001/jamaoncol.2022.0064

* DACHS study: colorectal cancer: chances of prevention through screening. More on this at:
DACHS .::. Homepage (dkfz.org)

** In adults, scientists speak of overweight from a Body Mass Index (BMI) of 25, and of obesity from a BMI of 30. BMI is a person's weight in kilograms divided by the square of height in meters.