Causal association of childhood obesity with cancer risk in adulthood: A Mendelian randomization study.

In observational studies of children and adolescents, higher body weight has been associated with distinct disease outcomes, including cancer, in adulthood. Therefore, we performed a two-sample Mendelian randomization (MR) study to evaluate the causal effect of childhood obesity on long-term cancer risk. Single-nucleotide polymorphisms associated with higher childhood body mass index (BMI) from large-scale genome-wide association studies were used as genetic instruments. Summary-level data for 24 site-specific cancers were obtained from UK Biobank. We found that a 1-SD increase in childhood BMI (kg/m2 ) was significantly associated with a 60% increase in risk of pancreatic cancer (odds ratio [OR]: 1.60; 95% confidence interval [CI]: 1.12-2.28; P < 0.01) and a 47% increase in risk of esophageal cancer (OR: 1.47; 95% CI: 1.09-1.97; P < 0.01) in adults. In contrast, there was an inverse association of genetic predisposition to childhood obesity with throat (OR: 0.46; 95% CI: 0.27-0.79; P < 0.01) and breast cancer (OR: 0.77; 95% CI: 0.64-0.94; P < 0.01) in adult life. For the other 20 cancers studied, no statistically significant association was observed. Our MR analyses found causal effects of childhood obesity on several cancers. Maintaining a healthy weight should be emphasized during childhood and adolescence to prevent cancer risk later in life.