In a new study from the University of Cambridge, researchers found obesity increases the risk of developing cancers of the digestive system and it is the person’s fat mass, rather than size, that is the main obesity-related risk factor for these cancer types.
Previous studies have shown that a high BMI (body mass index) is linked to several cancer types.
In the current study, the team used data from the UK Biobank and large international consortia to examine which cancers are causally linked to body size and how components such as fat mass, BMI and height affect this risk.
They studied whether genetic variants that predispose a person to have increased fat mass, BMI or being taller also predisposed them to have a higher risk of 22 different cancer types.
The researchers found genetic predisposition to being tall was consistently linked to slightly increased risk across the different cancer types.
Genetic predisposition to high BMI was linked to increased risk of cancers of the digestive system, particularly liver, stomach, esophageal and pancreatic cancer, but not with increased risk of overall cancer.
The increased risk of digestive system cancers was primarily attributable to genes that influence the fat mass.
This means that fat mass is a more important risk factor than body size and that high BMI is not necessarily a risk factor for many different cancer types, but mainly for cancers of the digestive system.
Moreover, genetic predisposition to increased BMI was linked to a higher risk of endometrial, ovarian, and lung cancer, but with a lower risk of breast and prostate cancer.
The study did not provide evidence about the mechanisms behind the associations, but the team thinks that tall people have a higher cancer risk because they have more cells in their bodies.
According to the researchers, the link between fat mass and digestive cancers may be driven by increased consumption of cancer-causing substances in fatty food, or increased levels of fatty tissue increasing inflammation in the digestive tract.
Links between obesity and gender-specific cancers are likely driven by the production of reproductive hormones in fatty tissue.
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The study is published in PLOS Medicine. One author of the study is Susanna Larsson.
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