Background Inflammatory bowel disease (IBD) is a chronic inflammatory disorder. Systemic inflammation increases the risk of atherosclerosis and ischaemic heart disease (IHD).

Objective To examine the impact of IBD, including its duration and treatment, on the risk of IHD.

Methods In a nationwide population-based cohort of 4.6 million Danes aged ≥15 years, we compared people diagnosed with IBD during 1997–2009 (n=28 833) with IBD-free individuals. Subjects with IHD were identified in the National Patient Register. Using Poisson regression, we estimated the incidence rate ratios (IRRs) for IHD with 95% CI with adjustment for age, gender, socioeconomic status, calendar year and use of drugs for comorbidities.

Results A markedly increased risk of IHD was seen within the first year after IBD diagnosis (IRR=2.13 95% CI 1.91 to 2.38). During 1–13 years of follow-up after IBD diagnosis, the risk of IHD was 1.22 (95% CI 1.14 to 1.30). The risk of IHD was lower among patients with IBD using 5-aminosalicylic acids (IRR=1.16; 95% CI 1.06 to 1.26) than among non-users (IRR=1.36; 95% CI 1.22 to 1.51) (p=0.02), in particular among oral corticosteroid users, used as a proxy for disease severity. Likewise patients treated surgically or with thiopurines and tumour necrosis factor α antagonists tended to have reduced IRRs for IHD.

Conclusions The risk of IHD was highest in the first year after IBD diagnosis, possibly owing to ascertainment bias. The increased long-term risk of IHD in IBD may be related to chronic inflammation, and interventions reducing the inflammatory burden may attenuate this risk.