Obesity increases the risk of cancer of the digestive tract and it is the amount of body fat rather than the size of the person that is the main obesity-related risk factor for these types of cancer. This is shown by a new study published in the journal PLOS Medicine by researchers at the University of Cambridge and Karolinska Institutet.
Previous observational studies have shown that a high BMI (body mass index) is linked to several cancers.
In the new study, researchers have used data from UK Biobank and large international consortia and a method called Mendelian randomization to investigate which types of cancer have a causal relationship between body size and cancer risk and how different components such as body fat, BMI and height affect this risk.
The researchers studied whether individuals with gene variants that are linked to high BMI, high body fat or above-average body length also have an increased risk of developing 22 different types of cancer.
– Body weight is often affected by the presence of cancer or by cancer treatment. Looking at genes rather than an individual’s height or weight reduces the risk of finding connections in observational data that are not causal, says Susanna Larsson , associate professor at the Institute of Environmental Medicine at Karolinska Institutet and shared last author of the article.
BMI and cancer of the digestive tract
Genetic propensity to be long was associated with a slightly increased risk for all different categories of cancer. Genetic predisposition to high BMI was mainly linked to an increased risk of cancer of the digestive organs, especially cancer of the liver, stomach, esophagus and pancreas.
The increased risk of cancer of the digestive organs could mainly be explained by gene variants that give an increased tendency to a lot of body fat.
– This means that body fat is a more important risk factor than body size and that high BMI is not necessarily a risk factor for many different types of cancer, but mainly for cancer of the digestive organs, says Susanna Larsson.
Genetic predisposition to high BMI was also linked to an increased risk of cancer of the uterus, ovaries and lungs, but a reduced risk of breast and prostate cancer.
Higher risk with more cells in the body
The study does not show the mechanisms behind the associations, but one hypothesis is that tall people have a higher risk of cancer because they have more cells in the body. According to the researchers, the link between body fat and cancer in the digestive organs may be due to greater consumption of carcinogens in fatty foods, or that more adipose tissue causes increased inflammation in the gastrointestinal tract.
The link between obesity and sex-specific cancers is likely to be affected by the production of sex hormones in adipose tissue.
The study was conducted in collaboration with researchers at the University of Cambridge and Bristol, UK. The researchers have not received any specific funding for the study.
Featured image: Illustration: Getty Images.
“Body size and composition and risk of site-specific cancers in UK Biobank and large international consortia: a Mendelian randomization study” . Mathew Vithayathil, Paul Carter, Siddhartha Kar, Amy M. Mason, Stephen Burgess, and Susanna C. Larsson. PLOS Medicine , online July 29, 2021, doi: 10.1371 / journal.pmed.1003706.
Provided by Karolinska Institute