Impact of obesity on the increasing incidence of type 1 diabetes.

Published estimates of the incidence of type 1 diabetes (T1D) in children in the last decade varies between 2% and 4% per annum. If this trend continued, the disease incidence would double in the next 20 years. The risk of developing T1D is determined by a complex interaction between multiple genes (mainly human leukocyte antigens) and environmental factors. Notwithstanding that genetic susceptibility represents a relevant element in T1D risk, genetics alone cannot explain the increase in incidence. Various environmental factors have been suggested as potential triggers for T1D, including several viruses and the hygiene hypothesis; however, none of these seems to explain the large increase in T1D incidence observed over the last decades. Several studies have demonstrated that the prevalence of childhood/adolescence overweight and obesity has risen during the past 30 years in T1D. Currently, at diagnosis, the majority of patients with T1D have normal or elevated body weight and ~50% of patients with longstanding T1D are either overweight or obese. The growing prevalence of obesity in childhood and adolescence offers a plausible explanation for the increase in T1D incidence observed in recent decades. Possible mechanisms of the enhancement of β-cell autoimmunity by obesity include: a) insulin resistance-induced β-cell secretory demand triggering autoimmunity through cytokine release, neo-epitope antigen formation and increase in β-cell apoptosis, and b) obesity-induced low-grade inflammation with pro-inflammatory cytokines secreted by locally infiltrating macrophages, which contribute to the presentation by islet cells of autoantigens generally not accessible to T cells. Further studies are needed to clarify whether the control of body weight can prevent or delay the current and continuing rise in T1D incidence.