BACKGROUND: Allergic and autoimmune diseases have been suggested to be inversely associated. We investigated the association between atopy and development of any and specific types of autoimmune disease.

METHODS: We included a total of 14,849 individuals from five population-based studies with measurements of atopy defined as specific IgE positivity against inhalant allergens. We followed the participants by linkage to the Danish National Patient Register (median follow-up time 11.2 years). Hazard ratio (HR) and 95% confidence interval (CI) of autoimmune disease were estimated by Cox regression.

RESULTS: The risk for atopics versus non-atopics was: for any autoimmune disease (HR = 0.99, 95% CI: 0.83, 1.18), thyrotoxicosis (HR = 0.69, 95% CI: 0.34, 1.37), type 1 diabetes (HR = 1.16, 95% CI: 0.84, 1.60), multiple sclerosis (HR = 1.97, 95% CI: 0.95, 4.11), iridocyclitis (HR = 0.82, 95% CI: 0.38, 1.74), Crohn's disease (HR = 1.03, 95% CI: 0.47, 2.25), ulcerative colitis (HR = 0.93, 95% CI: 0.52, 1.69), psoriasis vulgaris (HR = 1.50, 95% CI: 0.86, 2.62), seropositive rheumatoid arthritis (HR = 0.74, 95% CI: 0.48, 1.14) and polymyalgia rheumatica (HR = 0.79, 95% CI: 0.44, 1.44).

CONCLUSIONS: We found no statistically significant associations between atopy and autoimmune disease, but we cannot exclude relatively small to moderate effects - protective or promotive - of atopy on autoimmune disease.