Overweight and obese individuals with early stage type 2 diabetes had more severe and progressive abnormalities in brain structure and cognition compared to normal-weight study participants, according to a new study.
Chronic type 2 diabetes (T2D) is already known to increase the risk of a range of health problems in multiple organs throughout the body. Complications in the brain caused by the disease may accelerate cognitive dysfunction, and even increase the risk of dementia.
While the exact mechanism underlying how T2D alters the brain is not fully understood, several metabolic side effects including insulin resistance, poor blood sugar control, and inflammation have been suggested as playing a role.
Brain Effects Of Obesity And Diabetes
Obesity is linked to an increased risk of type 2 diabetes and can often precede its onset. Additionally, being overweight has been linked to metabolic dysfunction, which is independently associated with brain alterations, as well as carrying a risk of further exacerbating metabolic abnormalities arising from T2D.
Little is known, however, about the effect on the brain of excess weight or obesity in the presence of T2D.
The study recruited 150 Koreans between the ages of 30 and 60, comprising 50 overweight/obese individuals with T2D, 50 normal-weight individuals with T2D, and 50 normal-weight control individuals without diabetes. Participants were matched for age and sex across the three groups, and diabetic individuals were also matched for disease duration.
Individuals with chronic diabetic complications or major medical, neurological, or psychiatric disorders were excluded from the study, and all those with diabetes had been diagnosed within the previous 5 years and had not received stable insulin therapy.
Data about the structure of participants' brains were acquired using magnetic resonance imaging (MRI), which allowed the mean thickness of the cerebral cortex to be measured across its entirety. Participants also underwent cognitive assessments consisting of tests of memory, psychomotor speed, and executive function, as these are known to be affected in people with type 2 diabetes.
Grey Matter Thinning
The study found that grey matter was significantly thinner in clusters in the temporal, prefrontoparietal, motor and occipital cortices of the brains of diabetic study participants when compared to the non-diabetic control group. Further thinning of the temporal and motor cortices was also observed in the overweight/obese diabetic group, compared to normal-weight diabetics.
The team also discovered region-specific changes which suggested that the temporal lobe has a particular vulnerability to the combined effects of having type 2 diabetes and being overweight or obese.
Previous studies have already found that being overweight/obese or having T2D both increase the risk of dementia independently of one another. Atrophy of the temporal lobe has also been identified as one of the earliest observable changes in the large-scale structure of the brain in patients with Alzheimer’s disease.
The alterations to that region of the brain which were observed in this study may be an indication of how being overweight/obese, having T2D, and the risk of developing dementia are linked.
While the study notes that current WHO guidelines that use Body Mass Index (BMI) to classify individuals as overweight or obese do not differ according to ethnic origin, people of Asian ethnicity tend to be more vulnerable to slight increases in BMI, and are at higher risk of type 2 diabetes than other ethnicities. This vulnerability may be linked to differences at the cellular level as well as a tendency toward insulin resistance, even in lean individuals.
The authors note that the potential for ethnic differences in brain vulnerability to type 2 diabetes and/or obesity may need to be taken into account when interpreting their results.
The authors conclude:
“An increased awareness of overweight/obesity-related risk is necessary to prevent and manage type 2 diabetes-related brain atrophy and cognitive dysfunction from early stage T2D onward."
Yoon, S., Cho, H., Kim, J. et al. Brain changes in overweight/obese and normal-weight adults with type 2 diabetes mellitus Diabetologia (2017). doi:10.1007/s00125-017-4266-7
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