Combination of type 2 diabetes and smoking increases total cancer mortality in Japanese men using competing risk analysis: the Tanno-Sobetsu study

Aims: We assessed the impact of the combination of type 2 diabetes (T2DM) and smoking on total cancer mortality using cohort data of a general Japanese population. Methods: Of 1908 residents who received health checkups in two towns in 1994, 794 males were included as study participants. Smoking status was defined as three categories: never smoker, ex-smoker and current smoker. Individuals with T2DM were defined as individuals with fasting plasma glucose ≥7.0 mmol/l and/or receiving medication for T2DM. Participants were divided into six groups according to T2DM and smoking status: non-DM (NDM) and never smoker, NDM and ex-smoker, NDM and current smoker, DM and never smoker, DM and ex-smoker, and DM and current smoker groups. All participants were followed up for a maximum of 13 years. We calculated the hazard ratio (HR) using Cox’s proportional hazard model and subhazard ratio (SHR) using competing risk regression analyses in each group. Results: During the follow-up period, there were 169 all-cause deaths (62 cancer deaths and 40 CVD deaths). When using Cox regression analysis, HRs were higher in the ex-smoker and current smoker groups than in the never-smoker group, and HRs were also higher in the DM groups than in the NDM groups. When using competing risk analysis, SHRs were almost the same as the HRs of Cox regression analysis (DM and ex-smoker 6.06, DM and current smoker 10.12). Conclusions: The combination of T2DM and smoking is a strong risk factor for total cancer mortality in Japanese men. © 2015, The Japan Diabetes Society.