In the UK, 4.3 million people live with diabetes, while a further 850 000 could be living with the condition and be unaware of it (Diabetes UK, 2023). Type 2 diabetes mellitus is a chronic metabolic disorder, characterised by hyperglycaemia, and is associated with greater risks of heart disease, stroke, peripheral neuropathy, renal disease, blindness and amputation (Hurtado and Vella, 2019). Middle-aged and older adults with diabetes have a higher prevalence of frailty (Hanlon et al, 2018), an increased vulnerability associated with ageing, and experience a decline in the body's physical and psychological reserves (Turner, 2014). Both diabetes and frailty are independently associated with low self-rated health, depressive symptoms and low quality of life (O'Donovan et al, 2021).
In addition to physical frailty, cognitive impairment is increasingly recognised as a potential complication of diabetes, which may reflect a direct effect on the brain of hyperglycaemia or the effects of associated comorbidities such as hypertension (Luchsinger et al, 2018). Diabetes that is poorly controlled in older adults is also associated with double the risk of cognitive impairment no dementia (CIND) and triple the risk of CIND progressing to dementia (Dove et al, 2021).
Cognitive frailty is a clinical condition defined by the presence of both mild cognitive impairment and physical frailty (Yoshiura et al, 2022). Older adults with cognitive frailty are at higher risk of adverse health outcomes including death, disability, hospitalisation and incident dementia (Sugimoto et al, 2022). In older people with diabetes, cognitive frailty is also associated with an increased risk of mortality, greater than from either physical frailty or cognitive impairment alone (Abdelhafiz and Sinclair, 2019). A systematic review and meta-analysis by Lyu et al (2023) aimed to identify the prevalence of cognitive frailty and associated risk factors in community-dwelling older adults with diabetes.
Aim
This commentary aims to critically appraise the methods used within the review (Lyu et al, 2023) and expand upon the findings in the context of clinical practice and further research.
Methods
This systematic review and meta-analysis used a specific multi-database search from date of inception until 10 February 2022. Additional hand searching was undertaken of included studies and relevant systematic reviews. Only cross-sectional, longitudinal and cohort studies that reported the prevalence of cognitive frailty in community-dwelling older adults (aged 60+ years), with a diagnosis of diabetes, were included. Screening of included studies and assessment of quality were independently carried out by two reviewers. It was indicated that two reviewers carried out data extraction, but it was not stipulated that this was independent. A random effects meta-analysis was used to estimate the prevalence rates for cognitive frailty. Individual moderating risk factors were assessed using a pooled odds ratio (OR). Heterogeneity was assessed using the I2 statistic. Subgroup and meta-regression were undertaken to explore causes of heterogeneity. Publication bias was examined using visual inspection of funnel plot and relevant statistical tests.
Results
After duplicate removal, 1295 citations were identified; 15 full papers were included after screening. Studies included 6391 community-dwelling older adults with diabetes and took place in China (n=6), Italy (n=1), Japan (n=2), Malaysia (n=1), Mexico (n=1), Singapore (n=2) and the US (n=2). Most included studies were deemed to be of high quality (n=11) and the remaining four studies were classified to be of moderate quality.
The pooled prevalence of cognitive frailty within community-dwelling older adults with diabetes was 11% (95% confidence interval (CI=7.9% to 14%). There was statistically significant heterogeneity across studies (I2=95%). Using a take one away analysis, there was no significant difference from the removal of any single study for the estimated prevalence of cognitive frailty. There was no evidence of publication bias for both Eggers and Becks tests. When assessed using either subgroup analysis or meta-regression, there was no evidence of significant association for the factors of study design, sex, frailty instrument, cognition instrument, geographic region and study quality.
Exploration of the risk factors of cognitive frailty in community-dwelling adults with diabetes showed an increased odds for those who: have depression (OR 3.18, 95% CI=1.99–5.07), average blood glucose level (HbA1c) of ≥8.5% (OR=2.13; 95% CI=1.13-4.01), are aged >75 years (OR=2.10; 95% CI=1.15-3.82), or have sleep duration <5h (OR=1.98; 95% CI=1.08-3.61). Furthermore, there was a reduced odds of cognitive frailty for individuals who exercised (OR=0.56; 95% CI=0.36-0.88). There was no evidence of increased odds of cognitive frailty for sex, educational level, unmarried status, living alone, body mass index of ≥24kg/m2, disease duration greater than 10 years, HbA1c <7.0%, smoking and night sleep duration >8h.
Commentary
Using the Joanna Briggs critical appraisal checklist for systematic reviews and research syntheses (Joanna Briggs Institute, 2017), 10 out of 11 criteria were judged to be satisfactory for this review (Table 1). In the criterion for data extraction, it was unclear if the two reviewers undertook this task independently. The authors also note that due to limitations within the included study methodology, results should be treated cautiously due to the high heterogeneity between studies; for example, several assessment tools for cognitive frailty were used across studies. Furthermore, a limited number of studies reported risk factors in a uniform format and some studies failed to specify between type 1 or type 2 diabetes, or whether participants were on medications. However, the overall systematic review can be deemed to provide a comprehensive synthesis of the available evidence.
Table 1. Using the Joanna Briggs critical appraisal checklist for systematic reviews and research syntheses, 10 out of 11 criteria were judged to be satisfactory for this review
| Checklist | Criteria met |
|---|---|
| Is the review question clearly and explicitly stated? | Yes |
| Were the inclusion criteria appropriate for the review question? | Yes |
| Was the search strategy appropriate? | Yes, the search was conducted using Medical Subject Headings (MeSH) and free terms including frail, cognition and diabetes. Manual searching of relevant studies was also undertaken |
| Were the sources and resources used to search for studies adequate? | Yes, systematic searches of: PubMed, Web of Science, Cochrane Library, Embase, Cumulative Index of Nursing and Allied Health, Proquest, China National Knowledge Infrastructure and China Biology Medicine |
| Were the criteria for appraising studies appropriate? | Yes, the quality of included studies was assessed using Hoy et al's tool for assessing risk of bias in prevalence studies (Hoy et al, 2012) |
| Was critical appraisal carried out by two or more reviewers independently? | Yes, quality assessment was undertaken by two independent investigators and disagreements settled by discussion |
| Were there methods to minimize errors in data extraction? | Unclear, data extraction by two reviewers is stated but it is unclear if this was undertaken independently |
| Were the methods used to combine studies appropriate? | Yes, a random-effects model was used to combine data because of the heterogeneity present |
| Was the likelihood of publication biased assessed? | Yes, publication bias was assessed using funnel plot inspection, Begg's test and Egger's test |
| Were recommendations for policy and/or practice supported by the reported data? | Yes, recommendations for screening of cognitive frailty, standardisation of assessments, and targeted interventions were supported by the data |
| Were the specific directives for new research appropriate? | Yes, recommendations were made for future high-quality study to explore risk factors for cognitive frailty |
The pooled prevalence of cognitive frailty was estimated at 11%, highlighting the substantial burden of this condition within the older adult population with diabetes. It has previously been identified that cognitive frailty is a significant predictor of dementia and mortality in older adults living in the community and yet, there is no uniform assessment available to evaluate this condition (Bu et al, 2021). Therefore, evidence suggests there is a need for a comprehensive and multi-dimensional geriatric assessment that helps identify cognitive frailty in vulnerable older adults, in both clinical and community settings (Sugimoto et al, 2022). In the absence of a gold standard, community practitioners can utilise validated tools to assess for cognitive impairment such as the Mini-Mental State Examination (Creavin et al, 2016) or the Montreal Cognitive Assessment (Wei et al, 2022) in combination with a measure of physical frailty tests such as the Fatigue, Resistance, Ambulation, Illnesses and Loss of Weight (FRAIL) scale (Thompson et al, 2020), the Clinical Frailty Scale (Rockwood et al, 2020) or Fried's Frailty Phenotype Approach (Fried et al, 2001). Identifying cognitive frailty early, besides prevention and intervention measures, is recommended to reduce the occurrence of adverse outcomes caused by cognitive frailty (Bu et al, 2021).
Several factors were found to be associated with an increased risk of cognitive frailty. Individuals with depression, HbA1c ≥8.5%, aged over 75 years and with a sleep duration at night of <5 hours exhibited higher odds of cognitive frailty. These findings highlight the importance of addressing comorbidities such as depression and optimising glycaemic control, in the community setting. Given the association between depression and cognitive frailty in older adults with diabetes, it may be beneficial to integrate mental health assessments routinely through standardised depression scales, such as the Patient Health Questionnaire–9 (Levis et al, 2019) or the 15-item Geriatric Depression Scale (Shin et al, 2019).
The association between HbA1c levels ≥8.5% and cognitive frailty underscores the importance of glycaemic control in mitigating the risk of cognitive decline. Diabetic patients aged over 50 years old with uncontrolled blood glucose levels are at a higher risk of cognitive decline than individuals with controlled blood glucose levels (Koh et al, 2022). As such, community professionals should aim to educate patients about the relevance and importance of glycaemic control and testing for it, as there is a positive association between HbA1c self-awareness and blood glucose control (Almutairi et al, 2022). The National Institute for Health and Care Excellence guidelines (NICE, 2022) recommends measuring HBA1c in adults with type 2 diabetes every 3–6 months until stable and subsequently, every 6 months. Additionally, they recommend targets of 6.5% for individuals whose diabetes is managed by lifestyle/diet and 7.0% for those who take medication associated with hypoglycaemia.
Older adults with diabetes and those with shorter sleep durations also demonstrated increased odds of cognitive frailty. There is a bidirectional relationship between mild cognitive impairment and sleep disorders (Randhi et al, 2023). In addition to increased odds of cognitive frailty, later sleep timing and greater sleep variability may also be associated with other adverse health outcomes, including risk to cardiometabolic health (Chaput et al, 2020). There is a need to identify sleep disorders in older adults as soon as possible and not just regard them as a sign of aging (Randhi et al, 2023). To address difficulties with sleeping, patients in the community could be supported through information on maintaining good sleep hygiene, the importance of sleep (Randhi et al, 2023), and keeping sleep diaries or questionnaires to be more aware of sleep habits and sleep quality (Ibanez et al, 2018).
The review also found that individuals who exercised showed a decreased odds of cognitive frailty, although it was unclear whether the act of exercising provided protection or some aspect of a physical lifestyle. The World Health Organiaztion (WHO) have recommended that older adults aged 65 years and above should do at least 150 minutes of moderate intensity aerobic physical activity throughout the week (WHO, 2010). This includes recreational, leisure, transport, occupational, household or exercise activities. A higher level of physical activity is also associated with lower odds of frailty in community-dwelling older adults (Zhao et al, 2022). Furthermore, physical exercise for community-dwelling older adults with frailty promotes benefits in global cognition and mental flexibility (Rossi et al, 2021). Promotion of the benefits of physical activity to those in the community is therefore supported. NICE guidance suggests that tailored exercise and physical activity programmes of moderate intensity, including walking schemes, are recommended in the community setting to promote mental well-being in those aged over 65 years (NICE, 2008).
Future research would benefit from a focus on longitudinal studies that explore the trajectory of cognitive frailty and its relationship with diabetes management strategies. Such studies would enable the identification of temporal associations and causal relationships between cognitive frailty and risk factors such as glycaemic control, depression, sleep duration and exercise, helping to inform targeted interventions. A focus on developing a uniform assessment for cognitive frailty would also be welcomed.
Key points
- The pooled prevalence of cognitive frailty among community-dwelling older adults with diabetes was estimated at 11%, indicating a substantial burden of this condition
- The risk factors of depression, HbA1c (average blood glucose level) ≥8.5%, being aged over 75 years and sleep duration <5 hours were associated with cognitive frailty
- To support timely identification of cognitive frailty and treatment in the community, integrated mental health assessments, optimisation of glycaemic control and promoting good sleep hygiene may be beneficial
- There is a need for a comprehensive geriatric assessment for cognitive frailty in the community.
CPD reflective questions
- Which assessments for cognitive impairment and frailty could be integrated into practice?
- How could patient self-awareness of glycaemic control be improved?
- Are there any exercise or physical activity groups in the local area for older adults?