Impact of overweight and obesity on gastric and colorectal cancer incidence in the older adults: a nationwide cohort study

In the era of population ageing, research on age-related diseases, including cancers in the older adults, is important. This study aims to evaluate the impact of obesity on the risk of gastric cancer (GC) and colorectal cancer (CRC), particularly in the older adults. This is nationwide, population-based cohort study used on data from the Korean National Health Insurance Service (NHIS), including individuals aged ≥ 75 years who underwent national health screening between 2012 and 2015, followed-up until 2022. Risk factors and cumulative incidence curves for GC and CRC in this population were evaluated using the Fine-Gray method. Among total of 1,353,658 individuals, 21,853 (1.93%) GC and 30,685 (2.72%) CRC were diagnosed during the follow-up. Compared to normal weight, individuals in the highest body mass index (BMI) category showed positive correlation with increased risks of GC, CRC, and composite cancer (GC + CRC; adjusted hazard ratio 95% confidence interval: 1.113 1.024–1.210, 1.212 1.134–1.295, and 1.1621.101–1.226 for GC, CRC, and composite cancer, respectively). In contrast, underweight individuals showed decreased risks of GC, CRC, and composite cancer (0.858 0.803–0.917, 0.798 0.751–0.846, and 0.825 0.788–0.863, respectively). The cumulative incidence of GC and CRC was higher among individuals with overweight and class I obesity (BMI 25.0–29.99 kg/m2), particularly CRC. Furthermore, the co-existence of general obesity and abdominal obesity estimated using waist circumference was associated with an even greater risk of both GC and CRC. Overweight or obesity are modifiable risk factors for gastrointestinal cancers in the older adults. Maintaining a normal weight through appropriate weight control may have a beneficial effect on the prevention of gastrointestinal cancers in the older adults.