Methodological approaches to compile and validate a food composition database for methyl-group carriers in the European Prospective Investigation into Cancer and Nutrition (EPIC) study

•Standardised procedures were developed to compile a methyl-group carrier database.•The EPIC nutrient database was extended with choline, betaine and methionine.•The relative validity of the compiled methyl-group carrier database was confirmed.•The database is available for studying methyl-group carriers and cancer. A standardised methodology was used to compile and validate a methyl-group carrier database (MGDB) including folate, choline, betaine and methionine, for use in the European Prospective Investigation into Cancer and Nutrition (EPIC) study. Compilation was performed by following structured guidelines to match the EPIC dietary intake data to food items from four food composition databases, according to their assigned priority of use. To assess relative validity, calculated dietary folate intakes were compared between the MGDB and the EPIC nutrient database (ENDB), used as the reference database. Folate intakes based on the MGDB and those generated using the ENDB showed good agreement (weighted κ = 0.63) and were strongly correlated (r = 0.81). This MGDB can be used for investigating potential associations between methyl-group carrier intakes and risk or prognosis of cancer and other diseases in the EPIC study population.