Diabetes mellitus and risk of dementia: A meta-analysis of prospective observational studies

Degeneration of Dopaminergic Neurons Due to Metabolic Alterations and Parkinson's Disease

The rates of metabolic diseases, such as type 2 diabetes mellitus (T2DM), obesity, and cardiovascular disease (CVD), markedly increase with age. In recent years, studies have reported an association between metabolic changes and various pathophysiological mechanisms in the central nervous system (CNS) in patients with metabolic diseases. Oxidative stress and hyperglycemia in metabolic diseases lead to adverse neurophysiological phenomena, including neuronal loss, synaptic dysfunction, and improper insulin signaling, resulting in Parkinson’s disease (PD). In addition, several lines of evidence suggest that alterations of CNS environments by metabolic changes influence the dopamine neuronal loss, eventually affecting the pathogenesis of PD. Thus, we reviewed recent findings relating to degeneration of dopaminergic neurons during metabolic diseases. We highlight the fact that using a metabolic approach to manipulate degeneration of dopaminergic neurons can serve as a therapeutic strategy to attenuate pathology of PD.

Factors Associated with Changes in Brain Atrophy during a Three-Year Observation in Elderly Diabetic Patients: Effect of Renal Impairment on Hippocampal Atrophy

BACKGROUND/AIMS

We conducted a 3-year longitudinal study concerning factors associated with changes in brain atrophy in elderly diabetic patients.

METHODS

We evaluated hippocampal and global brain atrophy using automatic voxel-based morphometry of structural magnetic resonance images, 4 cognitive function tests, and cerebral small vessel disease (SVD) in 66 diabetic patients.

RESULTS

During the 3-year follow-up, hippocampal and global brain atrophy advanced, and cognitive functions worsened. For changes in hippocampal atrophy, changes in estimated glomerular filtration rate (eGFR), albuminuria, and being an ApoE ε4 carrier were independent factors; change in the number of silent brain infarctions was an independent factor for changes in global brain atrophy. A significant association of changes in eGFR and albuminuria with hippocampal atrophy remained after adjusting for confounders including SVD. Both types of brain atrophy at baseline were significantly correlated with cognitive impairment at baseline and especially associated with changes in delayed word recall during the follow-up after adjusting for confounders.

CONCLUSION

Changes in eGFR and albuminuria during follow-up were independent risk factors for hippocampal atrophy, which was associated with decline in delayed word recall, suggesting that management of chronic kidney disease may prevent the progression of hippocampal atrophy.

Type 2 Diabetes as a Risk Factor for Dementia in Women Compared With Men: A Pooled Analysis of 2.3 Million People Comprising More Than 100,000 Cases of Dementia

OBJECTIVE

Type 2 diabetes confers a greater excess risk of cardiovascular disease in women than in men. Diabetes is also a risk factor for dementia, but whether the association is similar in women and men remains unknown. We performed a meta-analysis of unpublished data to estimate the sex-specific relationship between women and men with diabetes with incident dementia.

RESEARCH DESIGN AND METHODS

A systematic search identified studies published prior to November 2014 that had reported on the prospective association between diabetes and dementia. Study authors contributed unpublished sex-specific relative risks (RRs) and 95% CIs on the association between diabetes and all dementia and its subtypes. Sex-specific RRs and the women-to-men ratio of RRs (RRRs) were pooled using random-effects meta-analyses.

RESULTS

Study-level data from 14 studies, 2,310,330 individuals, and 102,174 dementia case patients were included. In multiple-adjusted analyses, diabetes was associated with a 60% increased risk of any dementia in both sexes (women: pooled RR 1.62 [95% CI 1.45-1.80]; men: pooled RR 1.58 [95% CI 1.38-1.81]). The diabetes-associated RRs for vascular dementia were 2.34 (95% CI 1.86-2.94) in women and 1.73 (95% CI 1.61-1.85) in men, and for nonvascular dementia, the RRs were 1.53 (95% CI 1.35-1.73) in women and 1.49 (95% CI 1.31-1.69) in men. Overall, women with diabetes had a 19% greater risk for the development of vascular dementia than men (multiple-adjusted RRR 1.19 [95% CI 1.08-1.30]; P < 0.001).

CONCLUSIONS

Individuals with type 2 diabetes are at ∼60% greater risk for the development of dementia compared with those without diabetes. For vascular dementia, but not for nonvascular dementia, the additional risk is greater in women.

2015 Alzheimer's disease facts and figures

This report discusses the public health impact of Alzheimer’s disease (AD), including incidence and prevalence, mortality rates, costs of care and the overall effect on caregivers and society. It also examines the challenges encountered by health care providers when disclosing an AD diagnosis to patients and caregivers. An estimated 5.3 million Americans have AD; 5.1 million are age 65 years, and approximately 200,000 are age <65 years and have younger onset AD. By mid-century, the number of people living with AD in the United States is projected to grow by nearly 10 million, fueled in large part by the aging baby boom generation. Today, someone in the country develops AD every 67 seconds. By 2050, one new case of AD is expected to develop every 33 seconds, resulting in nearly 1 million new cases per year, and the estimated prevalence is expected to range from 11 million to 16 million. In 2013, official death certificates recorded 84,767 deaths from AD, making AD the sixth leading cause of death in the United States and the fifth leading cause of death in Americans age 65 years. Between 2000 and 2013, deaths resulting from heart disease, stroke and prostate cancer decreased 14%, 23% and 11%, respectively, whereas deaths from AD increased 71%. The actual number of deaths to which AD contributes (or deaths with AD) is likely much larger than the number of deaths from AD recorded on death certificates. In 2015, an estimated 700,000 Americans age 65 years will die with AD, and many of them will die from complications caused by AD. In 2014, more than 15 million family members and other unpaid caregivers provided an estimated 17.9 billion hours of care to people with AD and other dementias, a contribution valued at more than $217 billion. Average per-person Medicare payments for services to beneficiaries age 65 years with AD and other dementias are more than two and a half times as great as payments for all beneficiaries without these conditions, and Medicaid payments are 19 times as great. Total payments in 2015 for health care, long-term care and hospice services for people age 65 years with dementia are expected to be $226 billion. Among people with a diagnosis of AD or another dementia, fewer than half report having been told of the diagnosis by their health care provider. Though the benefits of a prompt, clear and accurate disclosure of an AD diagnosis are recognized by the medical profession, improvements to the disclosure process are needed. These improvements may require stronger support systems for health care providers and their patients.

Insulin resistance-induced hyperglycemia decreased the activation of Akt/CREB in hippocampus neurons: Molecular evidence for mechanism of diabetes-induced cognitive dysfunction

Several previous studies have indicated that diabetic have higher risk of suffering from Alzheimer's disease, which severely induced cognitive dysfunction. However, the underlying molecular mechanism and more details on the cognitive deficits induced by hyperglycemia have not been elucidated. Here in our present study, on the basis of Goto-Kakizaki (GK) rats and streptozotocin (STZ)-induced diabetic model, we detected the variation of dendritic spine density in hippocampus as well as the differential expression of some important signal transduction molecules that were of relevance in learning and memory function. We found that the magnitude of escape latency time was significantly increased in such diabetic animals; the phosphorylated Akt/CREB; SYP and BDNF as well as other downstream molecules in hippocampus neurons were also downregulated in both diabetic groups compared to the normal groups. Thus, all of these data indicate the obstacle of neuronal pathology and the Akt/CREB signaling pathway caused by hyperglycemia that may suppress cognitive behavior, which may provide a novel way for the prevention of diabetic encephalopathy and the cognitive deficits of Alzheimer's disease.

Impact of Type 2 Diabetes and Postmenopausal Hormone Therapy on Incidence of Cognitive Impairment in Older Women

OBJECTIVE

In older women, higher levels of estrogen may exacerbate the increased risk for cognitive impairment conveyed by diabetes. We examined whether the effect of postmenopausal hormone therapy (HT) on cognitive impairment incidence differs depending on type 2 diabetes.

RESEARCH DESIGN AND METHODS

The Women's Health Initiative (WHI) randomized clinical trials assigned women to HT (0.625 mg/day conjugated equine estrogens with or without [i.e., unopposed] 2.5 mg/day medroxyprogesterone acetate) or matching placebo for an average of 4.7-5.9 years. A total of 7,233 women, aged 65-80 years, were classified according to type 2 diabetes status and followed for probable dementia and cognitive impairment (mild cognitive impairment or dementia).

RESULTS

Through a maximum of 18 years of follow-up, women with diabetes had increased risk of probable dementia (hazard ratio [HR] 1.54 [95% CI 1.16-2.06]) and cognitive impairment (HR 1.83 [1.50-2.23]). The combination of diabetes and random assignment to HT increased their risk of dementia (HR 2.12 [1.47-3.06]) and cognitive impairment (HR 2.20 [1.70-2.87]) compared with women without these conditions, interaction P = 0.09 and P = 0.08. These interactions appeared to be limited to women assigned to unopposed conjugated equine estrogens.

CONCLUSIONS

These analyses provide additional support to a prior report that higher levels of estrogen may exacerbate risks that type 2 diabetes poses for cognitive function in older women. The role estrogen plays in suppressing non-glucose-based energy sources in the brain may explain this interaction.

Hippocampal insulin resistance and cognitive dysfunction

Clinical studies suggest a link between type 2 diabetes mellitus (T2DM) and insulin resistance (IR) and cognitive dysfunction, but there are significant gaps in our knowledge of the mechanisms underlying this relationship. Animal models of IR help to bridge these gaps and point to hippocampal IR as a potential mediator of cognitive dysfunction in T2DM, as well as in Alzheimer disease (AD). This Review highlights these observations and discusses intervention studies which suggest that the restoration of insulin activity in the hippocampus may be an effective strategy to alleviate the cognitive decline associated with T2DM and AD.

Bridging the Translation Gap: From Dementia Risk Assessment to Advice on Risk Reduction

Dementia risk reduction is a global health and fiscal priority given the current lack of effective treatments and the projected increased number of dementia cases due to population ageing. There are often gaps among academic research, clinical practice, and public policy. We present information on the evidence for dementia risk reduction and evaluate the progress required to formulate this evidence into clinical practice guidelines. This narrative review provides capsule summaries of current evidence for 25 risk and protective factors associated with AD and dementia according to domains including biomarkers, demographic, lifestyle, medical, and environment. We identify the factors for which evidence is strong and thereby especially useful for risk assessment with the goal of personalising recommendations for risk reduction. We also note gaps in knowledge, and discuss how the field may progress towards clinical practice guidelines for dementia risk reduction.

Glycemia, Diabetes Status, and Cognition in Hispanic Adults Aged 55-64 Years

OBJECTIVES

To examine the association of glycemia and diabetes status with cognition among 600 Hispanics aged 55 to 64 years from Northern Manhattan.

METHODS

Diabetes was ascertained by history or hemoglobin A1c. Normal glucose tolerance and prediabetes were ascertained with hemoglobin A1c. Memory was assessed with the Selective Reminding Test. Executive abilities were assessed using the Color Trails 1 and 2 and verbal fluency test. The cross-sectional association of glycemia and diabetes status with cognitive performance was examined using linear regression.

RESULTS

Participants had a mean age of 59.2 (2.9) years, 76.7% were women, and more than 65% had prediabetes or diabetes. HbA1C (β = -0.97, p < .001) and diabetes (β = -2.06, p = .001) were related with lower Selective Reminding Test total recall after adjustment for demographics, education, and vascular risk factors. Prediabetes was associated with worse performance in Color Trail 2 (β = -6.45 p = .022) after full adjustment.

CONCLUSIONS

Higher glycemia and diabetes are related to worse memory and executive abilities in late middle age, whereas prediabetes is related only to worse executive abilities. Longitudinal follow-up is needed to understand the order and progression of these deficits.

Tangzhining exhibits a protective effect against cognitive dysfunction in diabetic rats

Previous studies have suggested that diabetes significantly impairs the cognitive function. Tangzhining (TZN), as a kind of Traditional Chinese Medicine (TCM), has been widely used to treat diabetes in China. However, the effect of TZN on treatment of diabetes-induced learning and memory deficits has not been well documented. The present study was to investigate the effect of TZN on diabetes-induced learning and memory deficits and delineate the underlying molecular mechanism. Diabetic rats were randomly grouped and treated with various doses of TZN (0.47, 0.94 and 1.4 g/kg) by intraperitoneal injection. Using the Morris water maze, TZN treatment (0.94 g/kg and 1.4 g/kg) reduced markedly the escape latency and path length of diabetic rats. The morphological changes of pyramidal cells in hippocampus of diabetic rats were apparently reversed and improved by TZN treatment, in comparison with that in diabetic rats without TZN treatment. Moreover, the results of Western blot analysis showed that TZN treatment significantly increased the protein expression of glutamic acid decarboxylase (GAD) and excitatory amino acid carrier 1 (EAAC1) in hippocampus of diabetic rats. Furthermore, TZN treatment increased the protein expression of N-methyl-D-aspartic acid (NMDA) receptor subunits including NR1 and NR2B. Taken together, our data suggest that TZN sustains the balance between glutamate (Glu) and GABA by regulating GAD and EAAC1, and maintains the NMDA receptors activity for learning and memory function through regulating the subunits NR1 and NR2B.

Risk of dementia in patients hospitalised with type 1 and type 2 diabetes in England, 1998-2011: a retrospective national record linkage cohort study

AIMS/HYPOTHESIS

Type 2 diabetes increases the risk of subsequent dementia. Our objective was to determine whether a similar risk of subsequent dementia is associated with type 1 diabetes in a large defined population.

METHODS

This retrospective cohort study examined national administrative record-linked statistical data on hospital care and mortality in England, 1998-2011. Cohorts of people admitted to hospital when aged 30 or over were constructed: 343,062 people with type 1 diabetes; 1,855,141 people with type 2 diabetes; and a reference cohort. Results were expressed as rate ratios (RR) comparing each diabetes cohort with the control cohort.

RESULTS

The overall RR for dementia in people admitted to hospital with type 1 diabetes was 1.65 (95% CI 1.61, 1.68), and for people admitted to hospital with type 2 diabetes was 1.37 (1.35, 1.38). Young age at admission for diabetes appeared to confer a greater rate of subsequent dementia; the RR for dementia in people admitted to hospital with type 1 diabetes aged 30-39 years was 7.10 (4.65, 10.6), which reduced to 4.40 (3.55, 5.40) in those aged 40-49 at admission, and further reduced with increasing age to 1.16 (1.11, 1.20) in those aged 80 or over at admission. A similar pattern was seen with type 2 diabetes.

CONCLUSIONS/INTERPRETATION

Type 1 diabetes, as well as type 2 diabetes, may be associated with an elevated risk of subsequent dementia. The risk of dementia varies with age at admission to hospital with diabetes, and appears to be much greater in the young.

Link between type 2 diabetes and Alzheimer's disease: from epidemiology to mechanism and treatment

The aim of this paper is to provide a comprehensive review of the epidemiological evidence linking type 2 diabetes mellitus and its related conditions, including obesity, hyperinsulinemia, and metabolic syndrome, to Alzheimer’s disease (AD). Several mechanisms could help to explain this proposed link; however, our focus is on insulin resistance and deficiency. Studies have shown that insulin resistance and deficiency can interact with amyloid-β protein and tau protein phosphorylation, each leading to the onset and development of AD. Based on those epidemiological data and basic research, it was recently proposed that AD can be considered as “type 3 diabetes”. Special attention has been paid to determining whether antidiabetic agents might be effective in treating AD. There has been much research both experimental and clinical on this topic. We mainly discuss the clinical trials on insulin, metformin, thiazolidinediones, glucagon-like peptide-1 receptor agonists, and dipeptidyl peptidase-4 inhibitors in the treatment of AD. Although the results of these trials seem to be contradictory, this approach is also full of promise. It is worth mentioning that the therapeutic effects of these drugs are influenced by the apolipoprotein E (APOE)-ε4 genotype. Patients without the APOE-ε4 allele showed better treatment effects than those with this allele.

Prevalence and risk factors of development of peripheral diabetic neuropathy in type 2 diabetes mellitus in a tertiary care setting

AIMS/INTRODUCTION

The study was carried out to assess the prevalence of diabetic peripheral neuropathy (DPN), compare the prevalence between known diabetes mellitus (KDM) and newly detected diabetes mellitus (NDDM), identify risk factors associated, its prevalence pattern and to assess if any sex-specific differences are present.

MATERIALS AND METHODS

A cross-sectional study was carried out in a tertiary care hospital. Patients with duration of diabetes ≤6 months were considered to be NDDM. DPN was diagnosed by the combination of more than one abnormal result of 10-g monofilament, pinprick sensations and ankle reflexes, and categorized according to the severity level using vibration perception threshold. The study included 1,637 KDM and 369 NDDM patients.

RESULTS

A total of 586 participants were found to have DPN, accounting for 29.2% (95% confidence interval [CI] 27.2-31.2) prevalence. The higher prevalence was observed in KDM compared with NDDM 33.7% (95% CI 31.42-36.01) vs 9.2% (95% CI 6.3-12.2; P < 0.001). Prevalence of mild, moderate, and severe neuropathies was 8.06, 14.55 and 6.63%, respectively. Regression analysis showed age (P < 0.001), duration of diabetes (P < 0.001), dyslipidemia (P = 0.03), glycated hemoglobin (P < 0.001), the presence of other microvascular complications (P < 0.001), macrovascular complications (P = 0.003) and alcoholic status (P < 0.033) to be associated. No sex-specific differences were observed in the mean age at diagnosis of diabetes, mean age at the diagnosis of neuropathy, and duration taken for the DPN development among females and males.

CONCLUSIONS

The study showed a high prevalence (29.2%) of DPN among north Indian type 2 diabetes mellitus patients. Thus, timely screening with earlier detection and intervention would be useful in preventing the progression of neuropathy.

Non-communicable diseases in South Asia: contemporary perspectives

INTRODUCTION

Non-communicable diseases (NCDs) such as metabolic, cardiovascular, cancers, injuries and mental health disorders are increasingly contributing to the disease burden in South Asia, in light of demographic and epidemiologic transitions in the region. Home to one-quarter of the world's population, the region is also an important priority area for meeting global health targets. In this review, we describe the current burden of and trends in four common NCDs (cardiovascular disease, diabetes, cancer and chronic obstructive pulmonary disease) in South Asia.

SOURCES OF DATA

The 2010 Global Burden of Disease Study supplemented with the peer-reviewed literature and reports by international agencies and national governments.

AREAS OF AGREEMENT

The burden of NCDs in South Asia is rising at a rate that exceeds global increases in these conditions. Shifts in leading risk factors-particularly dietary habits, tobacco use and high blood pressure-are thought to underlie the mounting burden of death and disability due to NCDs. Improvements in life expectancy, increasing socioeconomic development and urbanization in South Asia are expected to lead to further escalation of NCDs.

AREAS OF CONTROVERSY

Although NCD burdens are currently largest among affluent groups in South Asia, many adverse risk factors are concentrated among the poor, portending a future increase in disease burden among lower income individuals.

GROWING POINTS

There continues to be a notable lack of national surveillance data to document the distribution and trends in NCDs in the region. Similarly, economic studies and policy initiatives addressing NCD burdens are still in their infancy.

AREAS TIMELY FOR DEVELOPING RESEARCH

Opportunities for innovative structural and behavioral interventions that promote maintenance of healthy lifestyles-such as moderate caloric intake, adequate physical activity and avoidance of tobacco-in the context of socioeconomic development are abundant. Testing of health care infrastructure and systems that best provide low-cost and effective detection and treatment of NCDs is a priority for policy researchers.