Abstract
Evidence is inconclusive regarding the associations of body size and occupational physical activity (PA) during the life course with gastrointestinal cancers. We analyzed data from the Golestan Cohort Study, a population-based, prospective cohort study from Iran, with 50 045 individuals aged 40-75 years enrolled during 2004-2008 and followed through April 2023. Body size during adolescence, early adulthood, and at cohort baseline was assessed using validated pictograms. Large adolescent body size was associated with total gastrointestinal cancers (hazard ratio [HR] = 1.09; 95% CI, 1.02-1.16) and liver cancer (HR = 1.49; 95% CI, 1.11-2.01). Large early-adulthood body size was associated with liver cancer (HR = 1.85; 95% CI, 1.35-2.52). Compared with normal weight during all stages, overweight or obesity during adolescence only or early adulthood only were associated with stomach cancer, esophageal squamous cell carcinoma, and liver cancer. Lower levels of adolescent occupational PA were associated with colon cancer (HR = 1.39; 95% CI, 1.10-1.75), whereas lower levels at cohort baseline were positively associated with colon cancer and inversely associated with rectal cancer. Our findings suggest that timing of obesity during the life course might differently affect risk of gastrointestinal cancers, whereas occupational PA was associated with colon cancer only.