Nutritional Epidemiology

Both diabetes and obesity are major public health problems, with an alarming increase in the numbers of people with these conditions. It has long been known that there is an important balance between energy intake in the form of food intake, and energy expenditure. However, the nature of the association between food intake and the risk for diabetes and obesity is poorly understood. There are confusing messages about what type of diets to eat, and what types of food to consume in what quantities, and what their effect is on the risk for diabetes or weight gain. Dietary intake is very difficult to measure, compounded by the limitations of the methods that have been used in the past to ascertain intake. Our research is important because it will help to address some of these pertinent issues by (1) using improved methods to assess dietary intake including measurement of blood-markers (called biomarkers) of food intake which are more accurate, (2) studying the association between diet and diabetes/obesity in large well conducted studies such as the EPIC-Norfolk cohort study, and (3) by collaborating with other scientists and groups who are doing similar research to increase further the size of studies and the resources available to adequately answer these questions. Examples of such collaboration include the InterAct Study with 12,403 cases of diabetes, making it the largest study in the world of these associations.

The aim of the nutritional epidemiology programme is to understand the aetiological associations between dietary and nutritional factors and the risk of type 2 diabetes, obesity and related metabolic disorders in order to inform preventive action. The contribution of dietary factors to the risk for diabetes and obesity is acknowledged to be important but major uncertainties exist about the nature of the relationship. This has often been the result of limitations in methods used to assess dietary intake, and has led to mixed, and often confusing messages about the role of dietary factors in promoting disease risk. Our objectives are to study the association of food intake and nutritional content with the risk for diabetes and related endpoints using dietary assessment instruments with greater precision as well as using biomarkers of dietary intake. Our methods include detailed dietary assessment by the self-reported semi-quantitative food frequency questionnaire as well as by the more precise 7-day prospective food diary. From these we derive key nutritional factors. To overcome issues of measurement error and reporting bias we have also measured candidate biomarkers of nutritional status such as plasma vitamin C, serum ferritin (body iron stores), and also serum vitamin D (a hormone, partly derived from the diet). We also await completion of measurement of serum fatty acids in the large EPIC-InterAct Study in European populations, which should provide invaluable information on the association between different types of dietary fat intake, which is particularly difficult to quantify from self-report because of the “invisible” fat in the diet. We use large-scale observational epidemiological studies including EPIC-Norfolk Study, the Fenland Study and InterAct, a case-cohort study of 12,403 incident cases of type 2 diabetes nested within the EPIC-Europe cohort. We also address the critical problems of confounding by using genetic variants as instrumental variables to assess the causal nature of the relationship between nutritional biomarkers and outcomes including diabetes, obesity and quantitative metabolic traits. We have also initiated a randomised double blind placebo controlled trial of the supplementation of vitamin D among people at high risk of diabetes, to assess whether vitamin D might be causally related to diabetes risk. In order to translate the findings of this programme into preventive action, we will also work as part of the Centre of Excellence in Diet and Activity Research (CEDAR) to develop collaborative work on understanding the determinants of dietary behaviour, and the development and evaluation of individual and collective dietary interventions.