Type 2 diabetes, when coupled with obesity, has a significant adverse effect on the temporal lobe of the brain.
The new research was the result of a collaboration between Dr. Sunjung Yoon and Dr. In Kyoon Lyoo, both of the Ewha Brain Institute at the Ewha Womans University in Seoul, South Korea, and Hanbyul Cho, of The Brain Institute at the University of Utah in Salt Lake City. Their findings were published in Diabetologia.
For example, type 2 diabetes is known to be associated with the progression of cognitive dysfunction and may amplify the risk of developing dementia. Scientists suggest that metabolic dysfunctions such as insulin resistance, inflammation, and poor sugar level control may all play a role in the brain alterations linked with type 2 diabetes, although exactly how this happens is not yet fully understood.
Obesity can potentially pave the way for the development of further conditions, and it is connected with a greater risk of developing type 2 diabetes. Moreover, obesity has a relationship with metabolic dysfunction and may worsen the metabolic abnormalities that are associated with type 2 diabetes. Furthermore, the metabolic dysfunction that is linked to obesity may be responsible for brain alterations and cognitive impairment, regardless of the presence of type 2 diabetes.
Previous studies have found independent links between obesity and type 2 diabetes and changes in the brain. However, little is known about how obesity and type 2 diabetes jointly affect the brain.
Yoon, Lyoo, Cho, and colleagues set out to explore the combined effects of obesity and type 2 diabetes on brain structure and cognitive function; they say that the rising prevalence of obesity may contribute to the global epidemic of type 2 diabetes.
The team focused on people who were in the early stages of type 2 diabetes and had received a diagnosis within the last 5 years. The recruited participants had not received stable insulin treatment.
Study participants included 150 people aged between 30 and 60 years. The participants were divided into three subgroups that were matched for age and sex. People with type 2 diabetes were matched for the duration of their condition. The three groups comprised 50 overweight or obese people with type 2 diabetes, 50 individuals of a healthy weight with type 2 diabetes, and 50 people of healthy weight without type 2 diabetes.
Temporal lobe particularly vulnerable to type 2 diabetes, obesity
Participants' brains were analyzed using MRI to evaluate the thickness of the cerebral cortex. Cognitive assessments to test memory, executive function, and psychomotor speed were also conducted, given the fact that these abilities are often affected by type 2 diabetes.
The researchers revealed that when compared with people of a healthy weight, individuals with type 2 diabetes exhibited significant thinning of gray matter in the temporal, prefrontoparietal, motor, and occipital cortices of the brain.
Gray matter of the temporal and motor cortices was thinner still in the obese diabetic group than in the group comprising healthy-weight diabetics. The temporal lobe, in particular, was found to be vulnerable in people with a combination of obesity and type 2 diabetes.
Wasting of the temporal lobe has previously been shown to be an early indicator of Alzheimer's disease. The region-specific changes that the researchers observed in the study may partly explain the mechanism linking obesity, type 2 diabetes, and the development of dementia.
"These findings suggest that weight status may play additive roles in type 2 diabetes-related brain and cognitive alterations," note the researchers.
"Our findings also highlight the need for early intervention aimed to reduce risk factors for overweight or obesity in type 2 diabetic individuals to preserve their brain structure and cognitive function."
While the specific factors that contribute to the brain alterations are not clear, managing insulin resistance during the early stages of type 2 diabetes could potentially make a difference.
The researchers point out that the study did not include people who were overweight or obese without diabetes. "Therefore, we could not determine the potential effects of overweight/obesity that are completely independent of type 2 diabetes on metabolic, brain, and cognitive measures," the authors conclude.