Joint association of the Mediterranean diet and smoking with all-cause mortality in the Seguimiento Universidad de Navarra (SUN) cohort

Although low-quality diets and smoking are independently associated with higher mortality risk, a joint analysis of both risk factors in relation to mortality has not been sufficiently studied. The aim of this study was to explore the effect modification between level of adherence to a Mediterranean dietary pattern (MedDiet) and smoking status on all-cause, cancer, and cardiovascular mortality. We conducted a prospective analysis to assess the association between diet and smoking status in the SUN (Seguimiento Universidad de Navarra) cohort study. Deaths were confirmed by review of the National Death Index. Participants were classified into six categories according to the MedDiet (adherence/non-adherence) and their exposure to smoking (never/former/current smoker). Multivariate-adjusted Cox regression models were fitted to estimate hazard ratios (HR) and 95% confidence intervals (CIs) for mortality. During a mean follow-up of 11.5 y (SD 4.5), we observed 18 948 participants (mean age 38.4 y; SD 12.4) and 431 deaths (51.3% cancer deaths). A higher risk for death was found among smokers with a low adherence to the MedDiet (HR, 2.20; 95% CI, 1.45–3.34) compared with never smokers with high adherence to the MedDiet. The P value for supra-multiplicative effect modification was not statistically significant, meaning that the effect of both factors is multiplicative. A higher risk for premature death from cancer was found in smokers and in those non-adherent with the MedDiet. Smoking and poor adherence to the MedDiet exerted a multiplicative effect in increasing all-cause mortality and cancer-related mortality in a Spanish population of university graduates.