“This is a huge cohort with a minimum follow-up of 10 years, and all individuals had measured BMI, not just reported or recalled,” Zohar Levi, MD, of the Rabin Medical Center and Tel Aviv University in Israel, said in a press release. “This is the largest study ever, including both men and women, and it had the power to prove the importance of BMI at age 17 on events later in life.”

Researchers observed a greater risk for colon cancer in men who were overweight (HR = 1.53; 95% CI, 1.28-1.84) and obese (HR = 1.54; 95% CI, 1.15-2.06) and women who were overweight (HR = 1.54; 95% CI, 1.22-1.93) and obese (HR = 1.51; 95% CI, 0.89-2.57).

The trend became significant after a BMI of 23.4 kg/m² in men and 23.6 kg/m² in women.

A greater risk for rectal cancer only occurred for obese men (HR = 1.71; 95% CI, 1.11-2.65) and women (HR = 2.03; 95% CI, 0.9-4.58). The trend became significant after a BMI of 29.6 kg/m² in men and 30.6 kg/m² in women.

The main limitation, Dr. Levi said, is that the cohort was still young, with the median age at colorectal cancer diagnosis of 49.4 years. The study also lacked data on diet, physical activity, and smoking, which might affect risk estimates. Family history of colorectal cancer was also unknown. Some Jewish populations are at higher risk for colorectal cancer as a baseline.

“Several explanations have been suggested for the association of a higher BMI with colorectal cancer,” the researchers wrote. “These include downregulation of adiponectin; upregulation of leptin, interleukin-6 and tumor necrosis factor alpha; increased insulin and insulin-like growth factor 1; the impact of nonalcoholic steatohepatitis; low-grade inflammation; and an altered immune response.”