My research has primarily focused on nutrition and cancer epidemiology. Main themes of my research have been determination of the role of plant-based diets, particularly fruit and vegetable intake, alcohol consumption, and more recently, vitamin D in the development of both common and less common cancers. Much of my research has been conducted in two international consortia that I have been leading/co-leading for over 16 years: the Pooling Project of Prospective Studies of Diet and Cancer (DCPP) and the Circulating Biomarkers and Breast and Colorectal Cancer Consortium (BBC3). Additionally, I have participated in several analyses of dietary factors including dietary patterns, anthropometric factors, and biomarkers within the Nurses' Health Study, Nurses' Health Study II, and Health Professionals Follow-Up Study, three large prospective cohort studies.