Nutritional and Lifestyle Factors for Cancer Incidence and Survival

Background: The association between meat consumption and breast cancer risk and the relationship between vitamin D and colorectal cancer risk have been examined in numerous studies, but questions still remain. For colorectal cancer survival, research into diet has been sparse. Methods: Chapter one is a pooled analysis of 22 prospective cohort studies examining meat and egg consumption and breast cancer risk overall and by estrogen and progesterone receptor (ER/PR) status using Cox proportional hazards models to estimate study-specific relative risks which were then pooled using random effects models. Chapter two is a pooled analysis of 17 prospective cohort studies in which the relationship between prediagnostic circulating 25-hydroxyvitamin D [25(OH)D] and colorectal cancer risk was explored using conditional logistic regression to calculate study-specific relative risks which were then pooled using random effects models. In Chapter three, the association between pre- and post-diagnosis sugar-sweetened beverage (SSB) and sugar intake and mortality among colorectal cancer patients was assessed using Cox proportional hazards models to estimate relative risks in two prospective cohort studies. Results: There were no significant associations between red and processed meat, seafood, and egg consumption and breast cancer risk, regardless of hormone receptor status. For poultry intake, there was a marginally statistically significant increased risk of ER+ and ER+PR- breast cancers only. We found that 25(OH)D concentrations were significantly inversely associated with colorectal cancer risk, with significant decreased risks for levels beyond current recommendations. These inverse associations were stronger in women than men. Pre-diagnosis total fructose, glucose, sucrose, and added sugar intakes were positively associated with mortality, but no association was observed for SSBs. In post-diagnosis analyses, there were marginally significant increases in all-cause mortality with higher intakes of fructose and glucose only. Conclusion: The results of the pooled analysis of meat and egg consumption and breast cancer risk provide some clarification on the inconsistent findings for these associations in individual studies, while the findings of the pooled analysis of 25(OH)D and colorectal cancer risk should be considered in developing public health guidelines on vitamin D. For colorectal cancer survival, future studies should explore pre- and post-diagnosis sugar intake and mortality.