Cognitive dysfunction in older subjects with diabetes mellitus: impact on diabetes self-management and use of care services
Introduction
Several studies have suggested that poor cognitive performance may be associated with Type 2 diabetes mellitus although an investigation of the aetiology or nature of this impairment or its clinical significance was not undertaken [1], [2], [3]. However, recent population-based cohort studies have suggested that older subjects with diabetes may be at increased risk of dementia [4], [5] whilst impaired glucose tolerance has also been linked to poor cognitive performance [6], [7].
In contrast, several studies of cognitive performance have reported little or no differences in subjects with Type 2 diabetes compared with control non-diabetic subjects [8], [9]. A preliminary study by our group using a neuropsychological battery of tests has also cast doubt on this association [10]. In this latter study, the lack of difference may have been due to a small group sample size (<30 subjects), and relatively good metabolic control (including control of blood pressure in those with hypertension) of study subjects with Type 2 diabetes. A recent community-based study with a more representative group of subjects found that those with known diabetes were more likely than non-diabetic subjects to have a low mental state examination score [11], and a critical review of 19 controlled studies concluded that sufficient evidence exists to link cognitive dysfunction with Type 2 diabetes [12].
Irrespective of the cause of cognitive impairment, its presence is likely to lead to changes in the ability of individual patients with diabetes to self-manage. This may compromise their empowerment role and co-operation with educational approaches which are important keys to effective management [13].
The purpose of the present study was, therefore, to determine whether diabetes mellitus (predominantly Type 2) in older subjects is associated with cognitive impairment of clinical importance which is likely to have an impact on day to day functioning and diabetes self-management. We used two simple but well-validated screening measures in a large community-based cohort of British subjects.
Section snippets
Research design
Subjects were recruited as part of the All Wales Research into Elderly (AWARE) Diabetes Study. This used a case control design to comprehensively evaluate morbidity, disability and quality of life and organisation of health care for elderly patients with diabetes mellitus living in both urban and rural sites in Wales.
The cohort of patients identified were aged 65 years or over and included all known cases of diabetes mellitus [14] in a sample of general practices in North, South and Mid-Wales.
Study population
Of the 571 subjects with diabetes mellitus, initially identified from general practice records, 96 were found to be ineligible (mainly because they were deceased, had moved out of the area or diagnosis of diabetes was not confirmed). Of the 475 eligible subjects, 16 were too ill to be interviewed, 49 refused consent, seven could not be contacted despite repeated efforts and seven could not attempt cognitive assessments because of severe visual impairment. Thus 396 (83%) of the eligible subjects
Discussion
Compared with an age- and sex-matched group of non-diabetic control subjects, this cross-sectional general practice study demonstrated the presence of greater prevalence of cognitive dysfunction (based on two simple cognitive screening tests) in an elderly group of subjects with predominantly Type 2 diabetes. A substantial excess of diabetic subjects had cognitive scores compatible with moderate to severe dementia. Evidence of significant underperformance in both measures of cognition in the
Acknowledgements
This study was supported by a grant from the Department of Health funded via the Welsh Office. Our special gratitude goes to Catherine Davies, Christine Corbett and Carys Brisbane for their commitment to the project, to the willing and supportive general practitioners and to Heather Copeland for help with data entry.
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