Language problems in women and insulin resistance – could it be a new dependency?

Dictionary Series - Health: diabetesFinnish researchers suggest that there is a link between insulin resistance (typical for type 2 diabetes) and language difficulties in women (a sign of cognitive disorders in dementia). The study included both men and women belonging to different age groups and was conducted by Laura Ekblad Ph.D. and colleagues from the University Hospital in Turku, Finland. The results of the research were published in “Diabetes”, journal of the European Association for the Study of Diabetes.

Both type 2 diabetes and Alzheimer’s disease are among the common diseases. There has been a constant increase in the number of patients with type 2 diabetes. Moreover, it is an independent risk factor for cognitive impairment and Alzheimer’s disease. There are various mechanisms that explain the effect of insulin resistance on the formation of cognitive disorders. Insulin has specific effects on the brain, and its transport across the blood-brain barrier is actively regulated. It undergoes a reduction in the case of peripheral hyperinsulinemia. Reduced insulin level in the brain can directly contribute to cognitive disorders and pathophysiology of Alzheimer’s in many ways. An example can be reducing the level of insulin-degrading enzyme in the brain, which plays an important role in the clearance of β-amyloid. Thus, lowered levels of these enzymes lead to excessive accumulation of β-amyloid in the brain. Insulin resistance, which occurs in middle age may increase the risk of cognitive impairment in later stages of life. Furthermore, alleles of apolipoprotein are well known risk factor for progression of Alzheimer’s disease and memory disorders in patients with mild cognitive impairment.

The authors of the hypothesis that insulin resistance is associated with cognitive decline and that gender and APOEε4 can modulate them, conducted a survey on a representative group of the Finnish adult population in a broad age range (30-97 years). Insulin was measured by the HOMA-IR method (Homeostasis Model Assessment). This group was also examined when it comes to verbal fluency to assess executive function, language and semantic memory. It was checked with a simple test. In this case participants were asked to provide the names of as many animals in 60 seconds as they could. The overall result of the test was the number of animals that have been mentioned. The authors of the test concluded that increased insulin resistance associated with poorer verbal fluency exists only in women.

Finnish researchers report that one of the possible causes of the different results for the two sexes are previously demonstrated lesions in the brain, which may indicate hyperintensivity of white matter (WMH) seen on functional magnetic resonance imaging. They are common in people with metabolic problems such as insulin resistance and are more common in women than in men. Scientists add that WMH seems to play a role in the pathology of Alzheimer’s disease. Therefore, the relationship between insulin resistance and cognitive disabilities can attest to the fact that it is a risk factor for Alzheimer’s disease. The risk may be regulated by several mechanisms. These include vascular damage and WMH or a direct effect of insulin resistance on the accumulation of β-amyloid peptide, the functional changes in the regional cerebral blood flow and glucose metabolism, or by combinations of these methods.

In conclusion, the researchers point out that the test results show that insulin resistance is strongly associated with poorer verbal fluidity among women, which reinforces previous reports of gender-specific action of insulin on cognitive function. Scientists emphasize, however, that although the verbal fluency is not the most sensitive means to identify early cognitive decline in adults, however, it binds well with insulin resistance in women and brain regions, that are under its negative impact.

Furthermore, the proportion of young and middle-aged adults in the study suggests that the relationship of insulin resistance and impaired cognitive function appears long before the emergence of serious defects in cognition. Scientists suggest that in the future the subject of long-term studies should be the causal relationship of insulin resistance and cognition.

Ph.D. Ekblad stresses that due to the fact that the results show that women may be more susceptible to the effects of insulin resistance on the cognitive functions than men, it is important to pay particular attention to preventive treatment, such as lifestyle changes for women at risk of type 2 diabetes or to the women with obesity. The results of the study seem to be promising.

Written by: Agata Zwierz, Klaudia Zyzak, Katarzyna Gałaszkiewicz

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