Adiposity and risks of gastrointestinal cancers: A 10‐year prospective study of 0.5 million Chinese adults

Associations of adiposity with risks of oesophageal squamous cell carcinoma (ESCC) and non-cardia stomach cancer, both prevalent in China, are still inconclusive. While adiposity is an established risk factor for colorectal cancer, the relevance of fat-free mass and early-adulthood adiposity remains to be explored. The prospective China Kadoorie Biobank study included 0.5 million adults (aged 30-79 years) from 10 areas in China. Participants' body size and composition were measured at baseline and at resurveys (amongst a subset). After >10 years of follow-up, 2350, 3345 and 3059 incident cases of oesophageal (EC), stomach (SC) and colorectal (CRC) cancers were recorded, respectively. Cox regression was used to estimate hazard ratios (HRs) for these cancers in relation to different adiposity traits. General and central adiposity were inversely associated with EC (primarily ESCC) risk, with HRs of 0.81 (95% CI 0.77-0.85), 0.76 (0.72-0.81) and 0.87 (0.83-0.92) per SD increase in usual levels of BMI, body fat percentage (BF%) and waist circumference (WC), respectively. Adiposity was also inversely associated with SC risk [HR = 0.79 (0.75-0.83) and 0.88 (0.84-0.92) per SD increase in usual BF% and WC], with heterogeneity by cardia and non-cardia subsites, and positively associated with CRC [HR = 1.09 (1.03-1.15) and 1.17 (1.12-1.22) per SD higher usual BF% and WC]. Fat-free mass was inversely associated with EC [HR = 0.93 (0.89-0.98) per SD increase] but positively associated with CRC [1.09 (1.04-1.14)], while BMI at age 25 was positively associated with all three cancers. After mutual adjustment, general adiposity remained inversely associated with EC and SC, while central adiposity remained positively associated with CRC.