Height, body mass index, physical activity, and risk of colorectal cancer in relation to expression of insulin receptor: The Japan Public Health Center-based Prospective Study

To ascertain the involvement of insulin receptors (IRs) in colorectal carcinogenesis, we investigated the association of height, body mass index (BMI), and physical activity with colorectal cancer (CRC) and two subtypes of CRC according to the expression level of IR. We utilized data from a large-scale, population-based prospective cohort study of 18,158 middle-aged and elderly subjects in Akita and Okinawa, Japan. In the statistical analysis, we used the Cox proportional hazards model and estimated hazard ratios (HRs) and 95% confidence intervals (CIs) for the risk of CRC and its subtypes as defined by immunohistochemistry of IR beta, a transmembrane subunit of IR. In the IR beta-defined subtypes, height showed no apparent association with the risk of IR beta-positive CRC. In contrast, a multivariable HR of IR beta-positive CRC was 1.77 (95% CI = 1.04-3.03) with a BMI of >= 30.0 kg/m(2) (i.e., obesity), compared to a BMI of <25.0 kg/m(2). Further, an increase in physical activity was significantly associated with decreased risk of IR beta-positive CRC (multivariable HR per 5 METs-hour/day = 0.93, 95% CI = 0.88-0.99). Meanwhile, we found no significant association between any exposure and IR beta-negative CRC. Likewise, heterogeneity between the two subtypes of CRC was not statistically significant. These findings imply that obesity and physical activity exert promoting and suppressing effects on the development of CRC expressing IRs, respectively.