[Controversies in the association between type 1 diabetes and asthma]. / Controvérsias na associação entre diabetes mellitus tipo 1 e asma.

OBJECTIVE: Critical review of the literature to investigate the relationship between asthma and type 1 diabetes mellitus (DM1). SOURCE OF DATA: Bibliography search in MEDLINE and LILACS databases in the last twenty years. SUMMARY OF DATA: Several studies demonstrate an inverse relationship between asthma, atopic diseases and the risk to develop DM1. According to the "Hygiene Hypothesis", the risk of allergic diseases decreases with infections early in childhood, towards distance of Th2 profile, common at birth, to the Th1 phenotype. Other articles described lack of association or positive association between DM1 and allergies. There is a possibility of environmental factors interfering in the development of disorders mediated by Th1 and Th2 cells, in the same individual, due to the absence of immunomodulatory mechanisms mediated by interleukin-10 and regulatory cells. CONCLUSION: The existing information about the inverse association between Th1-mediated diseases (e.g., DM1), and those that are Th2-mediated (e.g., allergies) are conflicting requiring more investigation to explain this question.