Heidelberg – Obesity is a known risk factor for colorectal cancer. Scientists at the German Cancer Research Center (DKFZ) have now proven that this connection has probably been significantly underestimated so far. The reason: Many people unintentionally lose weight in the years before a colorectal cancer diagnosis. If studies only take into account body weight at the time of diagnosis, this obscures the real connection between obesity and colorectal cancer risk. In addition, the current research shows that unintentional weight loss can be an early indicator of colorectal cancer.
Obesity is a risk factor for a number of cancers. This connection is particularly clear, for example, in the case of uterine cancer, kidney cancer and also colon cancer. According to previous estimates, obese people have about a third higher risk of developing colon cancer than people of normal weight.
“However, these studies have not yet taken into account the fact that many people affected lose weight in the years before their colorectal cancer diagnosis,” says Hermann Brenner, epidemiologist and prevention expert at the German Cancer Research Center has been underestimated.”
In order to estimate the magnitude of this distortion, the researchers led by Brenner evaluated the data from the DACHS study*. The almost 12,000 study participants who were included in the current analysis provided information about their body weight at the time of diagnosis and also their weight in the years of their earlier milestone birthdays.
Based on body weight at the time of diagnosis, there was no evidence of an association between body weight and colorectal cancer risk. However, it looked very different when the researchers looked at the previous body weight of the participants: Here there was a strong connection between obesity and the probability of developing colorectal cancer, which was most pronounced 8 to 10 years before the diagnosis. Study participants who were very overweight – known as obesity** or obese – during this period were twice as likely to develop bowel cancer as people of normal weight. “If, as in many previous studies, we had only looked at the weight measured at the start of the study, we would have completely overlooked the connection between obesity and an increased risk of colorectal cancer,” says Marko Mandic, the first author of the study.
In their analyses, Brenner’s team was able to identify another trend: a striking number of the study participants affected by colorectal cancer had unintentionally lost weight before the diagnosis. Unintentional weight loss of five pounds or more in the two years prior to diagnosis (or study entry) was 7.5 times more common among cancer patients than controls. “During this period, the cancer is already there, but not yet noticed by symptoms. GPs should therefore regularly ask their patients about unintentional weight loss,” says Brenner, adding: “Unintentional weight loss could also be an early indicator of other types of cancer or other diseases and should be carefully investigated.”
Marko Mandic, Fatemeh Safizadeh, Tobias Niedermaier, Michael Hoffmeister, Hermann Brenner: Association of Overweight, Obesity, and Recent Weight Loss With Colorectal Cancer Risk.
JAMA Network Open. 2023, doi:10.1001/jamanetworkopen.2023.9556
* DACHS stands for: “Colon cancer: chances of prevention through screening” and is one of the world‘s largest case-control studies on colon cancer, which it has been carried out at the German Cancer Research Center since 2003. Between 2003 and 2020, a total of 6,602 people affected by colon cancer took part and 7,950 people without colorectal cancer.
** Being overweight with a body mass index of ≥30 kg/m2 is considered adiposity or obesity
With more than 3,000 employees, the German Cancer Research Center (DKFZ) is the largest biomedical research facility in Germany. More than 1,300 scientists at the DKFZ research how cancer develops, record cancer risk factors and search for new strategies to prevent people from developing cancer. They are developing new methods with which tumors can be diagnosed more precisely and cancer patients can be treated more successfully. At the Cancer Information Service (KID) of the DKFZ, those affected, interested citizens and specialist groups receive individual answers to all questions on the subject of cancer. Together with partners from the university clinics, the DKFZ operates the National Center for Tumor Diseases (NCT) at the Heidelberg and Dresden sites, and the Hopp Children’s Cancer Center KiTZ in Heidelberg. In the German Consortium for Translational Cancer Research (DKTK), one of the six German Centers for Health Research, the DKFZ maintains translation centers at seven university partner locations. The combination of excellent university medicine with the top-class research of a Helmholtz center at the NCT and DKTK locations is an important contribution to transferring promising approaches from cancer research to the clinic and thus improving the chances of cancer patients. The DKFZ is funded 90 percent by the Federal Ministry of Education and Research and 10 percent by the state of Baden-Württemberg and is a member of the Helmholtz Association of German Research Centers.