Why do some people get type 1 diabetes? Researchers are still trying to figure it out. It's possible that combined genetic susceptibility and an environmental trigger -- perhaps a virus -- may cause this serious autoimmune disease.

When our bodies are humming along smoothly, we rarely think about all the complex processes that are going on. But when we don't feel well and we're unable to perform our usual activities, we want to know what's causing the problem and how it can be fixed. Type 1 diabetes is an autoimmune disease. Something triggers the body to mount an immune system attack against itself, in the same way the immune system normally attacks harmful bacteria and viruses.

In type 1 diabetes, the immune system produces antibodies that attack and destroy the insulin-secreting beta cells in the pancreas. As the number of beta cells decreases, the amount of insulin that is produced decreases as well. Fortunately, the immune system attack doesn't affect the body's ability to respond to insulin. That's why people with type 1 diabetes can compensate for the lack of insulin production by injecting insulin.

The cause of type 1 diabetes remains poorly understood, but a recent study reported in the journal Diadabetologia (volume 49, page 900) lends support to one leading theory. Some experts speculate that infections trigger type 1 diabetes in people who are genetically susceptible to diabetes. They believe that exposure to certain viruses may cause the immune system to mistakenly attack the pancreas and to destroy cells that produce insulin. If that's true, then outbreaks of viral infections within a community would likely cause "clusters" of new type 1 diabetes patients -- that is, an unusually large number of new diabetes diagnoses that arise over a brief period.

In the largest study of its kind to date, a group of British researchers examined the medical histories of more than 4,000 people under age 30 who were diagnosed with type 1 diabetes in Yorkshire, United Kingdom, between 1978 and 2002. The team discovered that new cases of type 1 diabetes often occurred in bunches, within confined sections of Yorkshire, specifically among youths ages 10-19. The study's findings suggest that something in the environment that people encounter on an irregular basis -- such as a virus -- may be more likely to cause type 1 diabetes than a more consistent environmental factor such as diet.