The mediating effect of Mediterranean diet on the relation between smoking and colorectal cancer: a case-control study

Background: The protective role of Mediterranean diet (MD) and the detrimental effect of smoking on colorectal cancer (CRC) have already been shown. The aim of this work was to evaluate the potential mediating effect of MD on the association between the aforementioned factor (smoking) and CRC. Methods: It is a case-control study. Two hundred fifty consecutive patients with CRC (63 +/- 12 years, 59% males) and 250 age-sex group-matched controls, both from the area of Attica, were studied. Various socio-demographic, clinical, lifestyle (including detailed smoking habits) and dietary characteristics were measured. Adherence to the MD was evaluated using the MedDietScore (theoretical range 0-55). Results: Each unit increase in the MedDietScore was associated with 13% lower likelihood of CRC (P < 0.001). Smoking habits were associated with 2.9-fold the likelihood of CRC among participants who were away from the MD (i.e. MedDietScore < 29) and with 2.1-fold the likelihood of CRC among those who were close to the MD (P < 0.05). Conclusions: Adherence to the MD was associated with a less detrimental association of smoking habits with CRC, suggesting indirect benefits of adherence to this dietary pattern with regards to CRC morbidity and mortality.