Chronic Inflammatory Disease, Lifestyle and Risk of Disease (PROCID-DCH)

Chronic inflammatory diseases (CID) - including inflammatory bowel diseases (Crohn's disease and ulcerative colitis), rheumatic conditions (rheumatoid arthritis, axial spondyloarthritis, psoriatic arthritis), inflammatory skin diseases (psoriasis) and multiple sclerosis are diseases of the immune system that have some shared genetic and environmental predisposing factors, but still little is known on the effects of lifestyle as a prognostic factor on disease risk. This observational study will contribute to preexisting research on lifestyle factors by identifying diet factors associated with risk of developing CID, using prospective register data.

The study will use data from all of the 57,053 participants in the Danish cohort "Diet, Health and Cancer (DHC)" together with registry data. Blood samples, anthropometric measures and questionnaire data on diet and lifestyle were collected at the DHC study entry. The National Patient Registry (NPR) will be used to obtain to identify patients with CID during follow-up. Follow-up information on death and immigration will be collected in March 2018 from the Danish Civil Registration Register.

The outcome CID is defined as at least one of the following CIDs: Crohn's disease, ulcerative colitis, psoriasis/psoriatic arthritis, rheumatoid arthritis/ankylosing arthritis, or multiple sclerosis, during the follow-up period from 1993 to March 2018.

The primary hypothesis is that "the risk of CID will be significantly higher among those with a low fibre/high red and processed meat intake compared to those with a high fibre/low red and processed meat intake." Based on previous research on a shared etiology in CIDs a second hypothesis is that "the postulated causality between low fibre/high red and processed meat intake and risk of developing CID is applicable for each of the CID-diagnoses."

The core study is an open register-based cohort study. The study does not need approval from the local Ethics committee or Institutional Review Board by Danish law. The study was approved by the Danish Data Protection Agency (2012-58-0018) Study findings will be disseminated through peer-reviewed journals, patient associations and presentations at international conferences.