The risk of colorectal cancer is known to increase with obesity. According to research by the German Cancer Research Center (DKFZ), this association has so far been severely underestimated. This is because many people mistakenly lose weight before receiving a diagnosis of colon cancer.
When studies only take into account body weight at the time of diagnosis, the true link between obesity and colorectal cancer risk becomes unclear. The new study also suggests that unintentional weight loss may serve as a precursor to colorectal cancer. There is a risk of many types of cancer due to obesity. For example, this connection is particularly evident in cases of colorectal, kidney and endometrial cancers. Previous estimates indicated that the risk of colon cancer in obese people was about a third higher than in people of normal weight.
“However, these studies have so far not taken into account that many affected people lose weight in the years before colorectal cancer diagnosis,” says Hermann Brenner, epidemiologist and prevention expert at the German Cancer Research Center. “This has led to a substantial underestimation of the risk contribution of obesity in many trials.” To assess the magnitude of this bias, the Brenner researchers evaluated data from the DACHS study*. The nearly 12,000 study participants included in the current evaluation provided information about their body weight at the time of diagnosis and also reported their weight in the years prior to diagnosis (measured at 10-year intervals).
Based on body weight at the time of diagnosis, no association could be established between body weight and colorectal cancer risk. The picture was quite different, however, when the researchers looked at participants’ earlier body weight: Here, a strong association was found between overweight and the likelihood of developing colorectal cancer, which was highest 8 to 10 years before diagnosis. was clear. Study participants who were excessively overweight — referred to as obese — were twice as likely to develop colorectal cancer during this period as those of normal weight. Marko Mandić, first author of the study, said, “If we had only looked at weight at baseline, as has been done in many previous studies, we may have completely missed the link between obesity and an increased risk of colorectal cancer. “