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Estimates of the severity of impairments in cognition per domain expressed in standardized effect sizes (Cohen's d) based on meta-analyses by Brands (43), Awad (49), Stewart (50) and their coworkers. The Cohen's d is defined as the difference between the means of two groups divided by the pooled standard deviation of the two groups. By expressing test performances of an experimental group relative to controls in Cohen's d standardized effect sizes, the results of different test that access the same domain can be pooled. It also facilitates comparison across different studies. In neuropsychological studies an effect size of 0.2 is generally considered to correspond to small effects, 0.5 to medium, and 0.8 to large effects (106).

Indeed several studies in elderly subjects with type 2 diabetes or "prediabetic" conditions such as impaired glucose tolerance, have detected cognitive impairment with relatively crude tests, such as a mini mental state examination, suggesting that the impairments may be more pronounced than in younger individuals (56,57). In a study of 400 type 2 diabetic patients and 400 nondiabetic controls with an average age of 75, for example, 29% of diabetic subjects scored below a mini mental state examination cut-of point of 24, compared with 12% of the controls (57). In the diabetic subjects a score lower than this cut-of point proved to have an impact on diabetes self-care and monitoring, and was also associated with higher hospitalisation, reduced ADL (activities of daily living) ability, and increased need for assistance in personal care.

During the past decade several large longitudinal population based studies have provided clear evidence that the incidence of dementia is increased among elderly patients with diabetes (Table 2). This appears to be related to both AD (relative risk 1.5-2) and vascular dementia (relative risk 2-2.5), although it can be difficult to distinguish between these types of dementia based on the clinical criteria that were used in these studies.

Depression

The next section of this chapter will address structural and neurophysiological changes in the brain that are likely to underlie changes in cognition. However, it should be noted that other factors can also influence cognitive function in diabetic patients. For example, the prevalence of psychiatric disorders in particular depressive and anxiety disorders, is increased in both type 1 and type 2 diabetes (58,59). A recent systematic review showed that the odds for the prevalence of depression among type 1 and type 2 diabetic patients are twice as high as in nondiabetic subjects (odds ratio [OR] 2, 95% CI 1.8-2.2) odd rate (59). The significance of clinical depression in diabetic patients should not be underestimated.

Dementia

Table 2

The Relative Risk of Incident Dementia in Diabetic Patients

Table 2

The Relative Risk of Incident Dementia in Diabetic Patients

References

Follow-up (years)

n Tot/DMa

Diagnosis6

Relative risk dementiac

107 (Japan)

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