Norfolk was chosen because few people in our age group of interest move out of the county, making it easier to follow our participants. Also, it is served mainly by one district general hospital, the Norfolk and Norwich University Hospital NHS Trust.

If a study is carried out on people who already had cancer, this may affect the way they reported what they have eaten in the past. Regardless of this, it is always difficult to describe what you were eating several years ago. A more accurate way of examining the effect of diet is to gather a great deal of lifestyle and nutritional information from a very large number of people. As time goes by, more and more information about this group is collected. If anybody in the group develops one of the diseases being studied, this is recorded. This type of investigation is called a cohort study. Using this study design, we should be able to make precise comparisons of how food intake can increase the risk of disease or – more interestingly – reduce it.

The original aim was to identify a cohort of 25,000 men and women from the general population of Norfolk. This cohort size was a compromise between the large numbers needed to get enough observations on people who developed cancer or other diseases, and the expense of making detailed measurements on everybody in the cohort. In fact, we recruited over 30,000 people to EPIC-Norfolk.

Cohort studies as large as EPIC are expensive to set up and run, though the results make the effort worthwhile. Other large cohort studies taking place at the moment include the Nurses’ Health Study, the Million Women Study, the Tomorrow Project. the Iowa Women’s Health Study and the Women’s Health Initiative.

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