Background: International multicentre studies on diet and cancer are relatively new in epidemiological research. They offer a series of challenging methodological issues for the evaluation of the association between dietary exposure and disease outcomes, which can both be quite heterogeneous across different geographical regions. This requires considerable work to standardize dietary measurements at the food and the nutrient levels.
Methods: Within the European Prospective Investigation into Cancer and Nutrition (EPIC), a calibration study was set up to express individual dietary intakes according to the same reference scale. A linear regression calibration model was used to correct the association between diet and disease for measurement errors in dietary exposures. In the present work, we describe an approach for analysing the EPIC data, using as an example the evaluation of the association between fish intake and colorectal cancer incidence.
Results: Sex- and country-specific attenuation factors ranged from 0.083 to 0.784, with values overall higher for men compared with women. Hazard ratio estimates of colorectal cancer for a 10 g/day increase in fish intake were 0.97 [95% confidence interval (CI): 0.95-0.99] and 0.93 (0.88-0.98), before and after calibration, respectively.
Conclusions: In a multicentre study, the diet/disease association can be evaluated by exploiting the whole variability of intake over the entire study. Calibration may reduce between-centre heterogeneity in the diet-disease relationship caused by differential impact of measurement errors across cohorts.