The study also found that, contrary to common clinical belief, diabetes may not be directly associated with small vessel ischemic disease, where the brain does not receive enough oxygenated blood.
"We found that patients having more severe diabetes had less brain tissue, suggesting brain atrophy," said lead author R Nick Bryan, professor of radiology at the Perleman School of Medicine at the University of Pennsylvania.
"They did not seem to have more vascular disease due to the direct effect of diabetes," said Bryan.
Type 2 is the most common form of diabetes. In it, either the pancreas does not produce enough insulin or the cells ignore the insulin that is produced.
"As diabetes becomes more common, better understanding of the disease and its management becomes even more important in order to minimise its effect on patient health," Bryan said.
For the study, Bryan and colleagues used magnetic resonance imaging (MRI) to investigate the association between severity and duration of type 2 diabetes mellitus and brain structure in 614 patients.
The mean duration of disease in the study group was 9.9 years. The researchers specifically tested whether more severe diabetes was inversely correlated with brain volumes and positively correlated with ischemic lesion volumes.
The results showed that longer duration of diabetes was associated with brain volume loss, particularly in the gray matter.
However, the study found no association of diabetes characteristics with small vessel ischemic disease in the brain.
"Diabetes duration correlated primarily with brain atrophy," Bryan said.
"Our results suggested that, for every 10 years of diabetes duration, the brain of a patient with diabetes looks approximately two years older than that of a non-diabetic person, in terms of gray matter volume," said Bryan.
The researchers noted that their findings may have implications for future decline of cognitive function in patients with diabetes and raise the possibility that such cognitive changes might not be strongly related to vascular dementia but to neurodegenerative disorders, like Alzheimer's.