MONDAY, May 1, 2023 (HealthDay News) — The association between excess weight and colorectal cancer (CRC) risk may be underestimated because of prediagnostic weight loss, according to a study published online April 21 in JAMA Network Open.

Marko Mandic, from the German Cancer Research Center in Heidelberg, Germany, and colleagues evaluated the association of body mass index (BMI) and weight change with CRC risk when considering BMI at different time frames. The analysis included 6,434 cases with a first diagnosis of CRC and 5,453 controls matched by age, sex, and county.

The researchers found that at the time of diagnosis, there was an inverse association between excess weight and CRC risk. When using BMI measured eight to 10 years before diagnosis, there was a significant positive association for overweight (adjusted odds ratio [aOR], 1.27), obesity (aOR, 2.09), and a 5-unit increase in BMI (aOR, 1.35) with CRC risk. As earlier periods before diagnosis were examined, high BMI as a risk factor for CRC increased, with the association particularly pronounced using BMI at least eight years before diagnosis. For weight loss (≥2 kg), an opposite trend was seen with CRC, with the greatest effect sizes occurring for weight loss within two years before diagnosis (aOR, 7.52) and gradually decreased for earlier intervals.

“These findings suggest that prediagnostic weight loss bias can lead to a considerable underestimation of the association of BMI with CRC,” the authors write.

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