Diabetes may be an immune disease
There is growing evidence that type 2 (adult-onset) diabetes is related to an underlying inflammatory process, suggesting that it is fundamentally a disease of the immune system.
The results of a large US study, reported in today's Journal of the American Medical Association, add weight to the theory. It showed that middle-aged women with higher blood levels of two chemical signals of inflammation were more likely to go on to develop diabetes.
Type 2 diabetes affects about 700,000 Australians, half of them undiagnosed, and is the nation's seventh-largest cause of death. It occurs when the body is unable to properly control blood sugar levels - not because the body does not produce enough insulin (as in juvenile-onset diabetes), but because the tissues become 'resistant' to it.
Family history, obesity, smoking, and lack of exercise increase the risk of type 2 diabetes, but its basic causes are not fully known. Better understanding could lead to earlier detection and prevention.
The US study, by Dr Aruna Pradhan and colleagues at the Brigham and Women's Hospital and Harvard Medical School, was part of the long-term Women's Health Study, involving female health professionals aged 45 years and older.
When the women enrolled in the study in 1992, the researchers measured their blood levels of two important chemicals. Called interleukin-6 (IL-6) and C-reactive protein (CRP), these chemicals are produced by the body as part of the the inflammatory process.
Four years later, 188 women who had developed diabetes were matched with 362 healthy women of similar age. When their original blood samples were compared, those with diabetes had higher levels of both IL-6 and CRP.
This adds to the results of previous studies, which have found higher levels of these marker chemicals in people with established diabetes. The new study shows an increase before the disease sets in, suggesting that the inflammatory process - in which the body reacts to injury by sending white blood cells and particular proteins to the damaged site - may be integral to disease progression.
The results are significant because inflammation is also thought to play a role in atherosclerosis - the build-up of plaques on arterial walls, which can eventually lead to a heart attack. Type 2 diabetes is known to increase the risk of heart disease.
However, it is too early to say that inflammation causes diabetes, the researchers point out. Both inflammation and diabetes could result from damage to the lining of blood vessels, for example, or from stored fat cells, especially those around the waist and stomach.