Background: Rheumatoid arthritis (RA) is a typical inflammatory arthritic disease that increases morbidity and mortality of cardiovascular diseases worldwide. Previous observational studies have shown potential for risk reduction through dietary factors modification, but associations between most of dietary factors and RA incidence are still uncertain, and evidence in United Kingdom populations is limited. Therefore, this study aims to assess associations between diet and RA incidence in the United Kingdom Women's Cohort.
Research plan and methods: The dietary and lifestyle data from the United Kingdom Women's Cohort, which recruited 35,372 middle-aged women between 1995-1998, will be used. These data were linked to Hospital Episode Statistics to provide data on the incidence of RA in participants.
Cox regression models will be applied to explore potential associations between dietary factors and RA incidence. Dietary factors will be modelled both as categorical and continuous variables so that models can be fit comparing the risk of RA between categories of intakes and per increment increase in exposure intake (linear dose-response). Restricted cubic splines will be used to model non-linear associations for dietary intake of alcohol, fruits, vegetables, tea, and coffee, since previous research has suggested possible non-linear associations for these variables.
