The association between measures of adulthood obesity, regional weight gain, and colorectal cancer risk: An Analysis of the NSW Cancer Lifestyle and Evaluation of Risk Study.

Abstract

Adulthood obesity is a known risk factor for colorectal cancer (CRC), but little is known about the effect of the duration of obesity on CRC risk. We studied the link between CRC risk and adulthood obesity, using body mass index (BMI) and regional weight gain, as proxies for overall and abdominal obesity, respectively. We analyzed all CRC cases (483 men and 373 women) and associated cancer-free controls (907 men and 965 women), from the NSW Cancer, Lifestyle and Evaluation of Risk Study. BMI was based on self-reported weight and height (kg/m2), at age 20 and before cancer diagnosis. Regional weight gain during participant's 20s and 30s and after age 50 was self-reported. Those with a BMI <25kg/m2 and >25kg/m2 were grouped as normal (reference) and overweight/obese, respectively. Regional weight gain was grouped as those who reported any weight gain in the abdomen, or in other regions versus no weight gain (reference). BMI at age 20 and before diagnosis were combined to derive the time course of obesity. We conducted a complete case analysis using logistic regression, adjusting for age, socioeconomic factors, alcohol intake, smoking status and physical activity, for the sexes separately. Although not seen in women, CRC risk was raised in men (odds ratio(OR)=1.48; 95% confidence interval(CI):1.13,1.93) who were overweight/obese before diagnosis compared to men with a normal BMI. Men who also were overweight/obese at age 20 had the highest CRC risk (OR=1.69;95%CI:1.22,2.34), men who had a normal BMI at age 20 had a lower, but still raised, CRC risk (OR=1.39;95%CI:1.04,1.87) compared to men with a normal BMI at both ages. Regional weight gain was not a CRC risk predictor in men or women. Health professionals should particularly encourage men to maintain a healthy weight, and for men who are overweight/obese at age 20 to monitor their weight during adulthood, and lose weight if they can, as early and prolonged exposure to obesity increases their CRC risk considerably.