The association between colorectal cancer (CRC) and overweight and obesity may be underestimated because body mass index (BMI) is typically measured too near the time of CRC diagnosis and so would not reflect prediagnostic weight loss linked to the condition, a new analysis suggests.
Obesity, assessed using BMI, was associated with twofold higher risk of CRC 8 to 10 years prior to diagnosis, while weight loss of 2 kg or more within 2 years of diagnosis was associated with a “dramatic” 7.52-fold increased risk of CRC, the researchers said.
The results “illustrate the dramatic change of BMI as a risk factor associated with CRC, depending on whether the period of potential prediagnostic weight loss is accounted for or not,” Hermann Brenner, MD, MPH, of the German Cancer Research Center, Heidelberg, and colleagues conclude.
The study was published online on April 21 in JAMA Network Open.
Recent evidence suggests that obesity is associated with an estimated 30% greater risk of CRC. But the extent to which excess body weight influences CRC risk may be underestimated because prediagnostic weight loss has historically been overlooked.
To understand how prediagnostic weight loss could affect the associations found between excess weight and CRC risk, the researchers examined weight data on almost 6500 patients newly diagnosed with CRC and more than 5400 control persons who were matched for age, sex, and country of residence. The median age of the cohort was 69 years, and 60.3% were men.
At the time of recruitment, 62% of case patients and 66% of control patients were overweight or obese. No association was found between current BMI and CRC risk.
However, when using patients’ weight from 8 to 10 years before CRC diagnosis, the researchers found a significant positive association between overweight or obesity and CRC risk (adjusted odds ratio [OR], 1.27 for overweight and 2.09 for obesity). The risk for CRC increased significantly for every 5-unit increase in BMI (OR, 1.35). These results were similar when the patients were stratified by sex and CRC subsites.
The researchers also found that weight loss of 2 kg or more within 2 years of CRC diagnosis or interview was associated with a 7.52-fold increased risk for CRC.
“While we demonstrated that prediagnostic weight loss is a major concern for CRC,” such prediagnostic weight loss “may play a similarly important role for other cancers and noncancer diseases associated with overweight and obesity,” the authors note.
“Most importantly, however, our results emphasize the importance of interventions aimed at preventing and managing overweight and obesity…and which may factor more substantially into CRC risk and other obesity-related diseases than suggested by existing epidemiological evidence,” they write.
The study was supported in part by grants from the German Research Council and the German Federal Ministry of Education and Research. The authors have disclosed no relevant financial relationships.
JAMA Netw Open. Published online April 21, 2023. Full text
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