Being Overweight Could Protect Against Dying From CRC, Says Kaiser Study

Men and women diagnosed with colorectal cancer (CRC) who were class I obese had the lowest risk of dying due to their cancer, according to a new study published in JAMA Oncology.

The study investigated the association between body mass index (BMI) and all-cause and cancer-specific mortality in more than 3400 men and women diagnosed with stage I to III CRC between 2006 and 2011. The authors of this study wanted to confirm the “obesity paradox,” namely individuals with higher BMI are more likely to be diagnosed with cancer, but once diagnosed, their prognosis is often better than normal-weight patients.

Candyce H. Kroenke, ScD, research scientist with the Kaiser Permanente Division of Research in Oakland, California, explained the hypothesis of their study in a statement. “Overweight and obesity have been identified as risk factors for many health conditions, but for people with colorectal cancer, some extra weight may provide protection against mortality,” she said.

For this retrospective study, the authors evaluated the electronic health records of 3408 men and women, 18 to 80 years of age, diagnosed with CRC and who had undergone surgery. These were Kaiser Permanente enrollees in Northern California. At diagnosis, a nonlinear association between BMI and all-cause mortality was observed, the authors report. Patients who were underweight (BMI <18.5; hazard ratio (HR), 2.65; 95% CI, 1.63-4.31) and patients who were class II or III obese (BMI ≥35; HR, 1.33; 95% CI, 0.89-1.98) exhibited elevated risk of mortality, compared with patients who were low-normal weight (BMI 18.5 to <23). However, patients who were high-normal weight (BMI 23 to <25; HR, 0.77; 95% CI, 0.56-1.06), low-overweight (BMI 25 to <28; HR, 0.75; 95% CI, 0.55-1.04), and high-overweight (BMI 28 to <30; HR, 0.52; 95% CI, 0.35-0.77) had lower mortality risks, and patients who were class I obese (BMI 30 to <35) showed no difference in risk.

While association with post diagnosis BMI and mortality were similar, patients who were class I obese had significantly lower all-cause and cancer-specific mortality risks.

“Our study, which represents the largest cohort of colorectal cancer patients with the most comprehensive data regarding patient weight before, at time of, and following diagnosis, supports the notion of the 'obesity paradox’,” Kroenke said.

Senior study author Bette J. Caan, DrPH, explained that similar to different treatments based on cancer, ideal weight recommendations may vary based on cancer site.

Reference

Kroenke CH, Neugebauer R, Meyerhardt J, et al. Analysis of body mass index and mortality in patients with colorectal cancer using causal diagrams [published online May 19, 2016]. JAMA Onc.