Countries with lower death rates from infectious diseases have higher incidences of type 1 diabetes, researchers from the University of Malta explained at the Society for Endocrinology annual conference in Harrogate, UK. Their study was also published in Acta Diabetologica.

The researchers explained that type 1 diabetes rates have been steadily increasing by 3% annually for over a decade. This increase in reported cases has occurred mainly in rich nations. However, so far nobody has understood why.

Experts have offered various theories, including the hygiene hypothesis, which suggests we are genetically designed to be in contact with micro-organisms – if babies and young children are over-protected from germs and dirt their immune system does not develop properly and the likelihood of auto-immunity increases. In other words, evolution has made us the way we are; we are animals that need to be in contact with micro-organisms such as parasites, viruses and bacteria early in life for our immune systems to develop and work properly.

Type 1 diabetes occurs when our immune system destroys the insulin-producing beta cells in the pancreas, leaving the patient unable to control his/her own blood sugar.

At some stage of a type 1 diabetes person’s life (usually before 20 years of age), their immune system confused the healthy beta cells with foreign, undesirable, dangerous pathogens (disease-causing micro-organisms), and attacked and destroyed them. Swedish scientists have managed to stop the immune system from destroying beta cells in animal experiments.

Professor Stephen Fava and Prof. Alexia-Giovanna Abela set out to determine whether infectious disease burden might be linked to the local incidence of type 1 diabetes. They collected data from three large international studies:

  • WHO (World Health Organization) DiaMond Project
  • WHO Global burden of disease
  • The Alexander Project

The data were used to correlate type 1 diabetes rates by country with infectious disease mortality and bacterial antibiotic susceptibility (which indicates the quantity of antibiotics being used as well as people’s exposure to bacterial infection).

The authors found that:

  • Countries with low mortality from infectious disease (rich countries) had the highest incidences of type 1 diabetes
  • This held true for both infectious disease mortality, as well as deaths caused by TB (tuberculosis), other respiratory diseases, diarrhea, and parasitic disease.

  • They also found positive associations between the incidence of type 1 diabetes and antibiotic susceptibilities of Strep. Pneumoniae, but not to those of Haem. Influenza.

Prof. Fava said that their findings suggest that there may well be a reverse association between type 1 diabetes incidence and the burden of infectious disease – the more infectious diseases there are in a country, the lower their rate of type 1 diabetes.

The rising rate of type 1 diabetes worldwide may be associated with low exposure to pathogens during a person’s first years of life, the team believe.

The data gathered and examined by Alexia-Giovanna Abela and Stephen Fava support the hygiene hypothesis, but do not prove it. This is a study of simple association; the increase in type 1 diabetes incidence is a complex problem.

The authors say they wish to utilize additional studies to find out whether there are other environmental factors which may impact on type 1 diabetes risk.

Prof. Fava said:

“The global rise in type 1 diabetes is an unexplained phenomenon. Many suggest that the exposure, or rather the lack of exposure, to infectious disease when young might be linked to the development of autoimmunity. Our data show that type 1 diabetes rates were highest in countries where markers of exposure to infectious disease were lowest.

Incidence of type 1 diabetes was significantly linked to mortality from a variety of infectious diseases and to the local susceptibility of a common bacterium to antibiotics.

He added:

“These data provide support for the notion that the immune system can somehow become disordered and attack the body’s own cells if it is not trained by regular exposure to micro-organisms – the so called hygiene hypothesis. More research is needed to try to identify other environmental factors that may be linked to the continuing conundrum of rising type 1 diabetes rates.”

A study published in the BMJ (September 2011 issue) revealed that although type 1 diabetes patients are living longer compared to thirty years ago, more are dying from alcohol-related problems.

The authors also found that while patients who developed type 1 before the age of 14 have better survival rates today compared to the early 1980s, those who developed the disease from ages 15 to 29 years have not.

Written by Christian Nordqvist