Negative association between occurrence of type 1 diabetes and tuberculosis incidence at population level

In the last decades of the 20th century, the incidence rate of type 1 diabetes increased in affluent countries. The pattern of occurrence of this autoimmune disease over time could provide helpful information to discriminate between alternative aetiologic hypotheses. In addition to genetic disposition, the incidence of type 1 diabetes seems to be conditioned by environmental factors and lifestyle. One theory proposes that the increase in the prevalence of autoimmune diseases is a result of the decrease in the incidence of childhood infections. To investigate the relationship between the incidence of type 1 diabetes and the decline of infectious diseases, we calculated the correlation between the occurrence of type 1 diabetes and tuberculosis in several European and non-European countries. The results of our analysis demonstrate an inverse correlation between the occurrences of type 1 diabetes and tuberculosis. A possible interpretation of this negative association is that a high socio-economic status and a westernised way of life imply a reduced or delayed exposure to infectious agents and so a reduced or delayed "pressure" on the immune system, which is free to mount inappropriate responses against self-antigens, as happens in type 1 diabetes.