Prediagnosis body mass index and waist–hip circumference ratio in association with colorectal cancer survival

The association of obesity on survival among patients with colorectal cancer (CRC) has not been well characterized. We investigated the association of prediagnostic body mass index (BMI)/waist–hip ratio (WHR) and total/cause‐specific mortality in CRC patients. Our study included 1,452 patients who participated in two large cohort studies and were diagnosed with CRC during follow‐up period. Participants were measured for anthropometrics and interviewed to collect relevant information at baseline, prior to any cancer diagnosis. Data on site‐specific cancer incidence and cause‐specific mortality were obtained via in‐person surveys and annual record linkage with cancer and vital statistics registries. Cox proportional hazard models were used to evaluate the associations of BMI and WHR with survival. A total of 547 participants died during the follow‐up period, including 499 who died of CRC. Relative to normal BMI (18.5 to <25.0 kg/m²), obesity (BMI ≥ 30 kg/m²) was associated with increased mortality resulting from all causes hazard ratio (HR) = 1.5, 95% confidence interval (CI): 1.1–2.1] and CRC (HR = 1.5, 95% CI: 1.1–2.1). Elevated risk of death was also found among underweight patients (BMI < 18.5 kg/m²), although not all risk estimates were statistically significant. Overweight BMI (25.0 to <30.0 kg/m²) was not associated with risk of death among CRC patients, nor was WHR. In conclusion, prediagnostic BMI was associated with survival among CRC patients following a U‐shape pattern; obesity was associated with high mortality after CRC diagnosis. These findings provide support for maintaining healthy weight to improve the survival of CRC patients.