Risk factors for Alzheimer's disease: a case-control study

Comorbidity and dementia: A nationwide survey in Taiwan

BACKGROUND

Comorbid medical diseases are highly prevalent in the geriatric population, imposing hardship on healthcare services for demented individuals. Dementia also complicates clinical care for other co-existing medical conditions. This study investigated the comorbidities associated with dementia in the elderly population aged 65 years and over in Taiwan.

METHODS

We conducted a nationwide, population-based, cross-sectional survey; participants were selected by computerized random sampling from all 19 Taiwan counties between December 2011 and March 2013. After exclusion of incomplete or erroneous data, 8,456 subjects were enrolled. Of them, 6,183 were cognitively normal (control group), 1,576 had mild cognitive impairment (MCI), and 697 had dementia. We collected information about types of comorbidities (i.e., vascular risk factors, lung diseases, liver diseases, gastrointestinal diseases, and cancers), Charlson comorbidity index score, and demographic variables to compare subjects with normal cognition, MCI, and dementia.

RESULTS

Regardless of the cognitive condition, over 60% of the individuals in each group had at least one comorbid disease. The proportion of subjects possessing at least three comorbidities was higher in those with cognitive impairment (MCI 20.9%, dementia 27.3%) than in control group (15%). Hypertension and diabetes mellitus were the most common comorbidities. The mean number of comorbidities and Charlson comorbidity index score were greater in MCI and dementia groups than in control group. Logistic regression demonstrated that the comorbidities significantly associated with MCI and dementia were cerebrovascular disease (OR 3.35, CI 2.62-4.28), cirrhosis (OR 3.29, CI 1.29-8.41), asthma (OR 1.56, CI 1.07-2.27), and diabetes mellitus (OR 1.24, CI 1.07-1.44).

CONCLUSION

Multiple medical comorbid diseases are common in older adults, especially in those with cognitive impairment. Cerebrovascular disease, cirrhosis, asthma, and diabetes mellitus are important contributors to cognitive deterioration in the elderly. Efforts to lower cumulative medical burden in the geriatric population may benefit cognitive function.

EVALUATION OF HOW CIGARETTE SMOKE IS A DIRECT RISK FACTOR FOR ALZHEIMER'S DISEASE

Cigarette smoking is a risk for Alzheimer's disease (AD), the pathological hallmark of which is amyloid-β (Aβ) brain deposits. We found the adjusted risk of AD was significantly increased among medium level smokers (RR = 2.56; 95% CI = 1.65-5.52), with an even higher risk in the heavy smoking group (RR = 3.03; 95% CI = 1.25-4.02). This systematic review and original data further support this association. We searched Pubmed, Google scholar, and PsyINFO for original population study articles, meta-analyses, and reviews published between 1987 and 2011. Some studies were excluded due to design flaws including survivor bias. We performed analyses of: 1) amyloid precursor protein (APP) processing in N2a cells overexpressing Swedish mutant APP (SweAPP N2a) exposed to cigarette smoke condensate (CSC), 2) microglial inflammatory response to CSC, and 3) CSC exposed microglial phagocytosis of Aβ(1-42). CSC significantly promotes neuronal Aβ generation, increases microglial IL-1β and TNF-α production, and decreases microglial Aβ(1-42) phagocytosis. The mechanism underlying the epidemiological association of cigarette smoking with AD might involve the effect of cigarette smoke on APP processing, a reduction of Aβ clearance by microglia, and/or an increased microglial proinflammatory response. In vivo studies are required to fully elucidate how cigarette smoke promotes AD.

Cigarette smoking is a risk factor for Alzheimer's Disease: an analysis controlling for tobacco industry affiliation

To examine the relationship between smoking and Alzheimer's disease (AD) after controlling for study design, quality, secular trend, and tobacco industry affiliation of the authors, electronic databases were searched; 43 individual studies met the inclusion criteria. For evidence of tobacco industry affiliation, http://legacy.library.ucsf.edu was searched. One fourth (11/43) of individual studies had tobacco-affiliated authors. Using random effects meta-analysis, 18 case control studies without tobacco industry affiliation yielded a non-significant pooled odds ratio of 0.91 (95% CI, 0.75-1.10), while 8 case control studies with tobacco industry affiliation yielded a significant pooled odds ratio of 0.86 (95% CI, 0.75-0.98) suggesting that smoking protects against AD. In contrast, 14 cohort studies without tobacco-industry affiliation yielded a significantly increased relative risk of AD of 1.45 (95% CI, 1.16-1.80) associated with smoking and the three cohort studies with tobacco industry affiliation yielded a non-significant pooled relative risk of 0.60 (95% CI 0.27-1.32). A multiple regression analysis showed that case-control studies tended to yield lower average risk estimates than cohort studies (by -0.27 +/- 0.15, P=0.075), lower risk estimates for studies done by authors affiliated with the tobacco industry (by -0.37 +/- 0.13, P=0.008), no effect of the quality of the journal in which the study was published (measured by impact factor, P=0.828), and increasing secular trend in risk estimates (0.031/year +/- 0.013, P=0.02). The average risk of AD for cohort studies without tobacco industry affiliation of average quality published in 2007 was estimated to be 1.72 +/- 0.19 (P< 0.0005). The available data indicate that smoking is a significant risk factor for AD.

Nicotinic effects on cognitive function: behavioral characterization, pharmacological specification, and anatomic localization

RATIONALE

Nicotine has been shown in a variety of studies in humans and experimental animals to improve cognitive function. Nicotinic treatments are being developed as therapeutic treatments for cognitive dysfunction.

OBJECTIVES

Critical for the development of nicotinic therapeutics is an understanding of the neurobehavioral bases for nicotinic involvement in cognitive function.

METHODS

Specific and diverse cognitive functions affected by nicotinic treatments are reviewed, including attention, learning, and memory. The neural substrates for these behavioral actions involve the identification of the critical pharmacologic receptor targets, in particular brain locations, and how those incipient targets integrate with broader neural systems involved with cognitive function.

RESULTS

Nicotine and nicotinic agonists can improve working memory function, learning, and attention. Both alpha4beta2 and alpha7 nicotinic receptors appear to be critical for memory function. The hippocampus and the amygdala in particular have been found to be important for memory, with decreased nicotinic activity in these areas impairing memory. Nicotine and nicotinic analogs have shown promise for inducing cognitive improvement. Positive therapeutic effects have been seen in initial studies with a variety of cognitive dysfunctions, including Alzheimer's disease, age-associated memory impairment, schizophrenia, and attention deficit hyperactivity disorder.

CONCLUSIONS

Discovery of the behavioral, pharmacological, and anatomic specificity of nicotinic effects on learning, memory, and attention not only aids the understanding of nicotinic involvement in the basis of cognitive function, but also helps in the development of novel nicotinic treatments for cognitive dysfunction. Nicotinic treatments directed at specific receptor subtypes and nicotinic cotreatments with drugs affecting interacting transmitter systems may provide cognitive benefits most relevant to different syndromes of cognitive impairment such as Alzheimer's disease, schizophrenia, and attention deficit hyperactivity disorder. Further research is necessary in order to determine the efficacy and safety of nicotinic treatments of these cognitive disorders.

Nicotinic receptor mechanisms and cognition in normal states and neuropsychiatric disorders

Cigarette smoking rates in the American population are approximately 23%, whereas rates of smoking in clinical and population studies of individuals with neuropsychiatric disorders are typically two- to four-fold higher. Studies conducted in a variety of neuropsychiatric populations [e.g. attention-deficit hyperactivity disorder (ADHD), Alzheimer's disease, schizophrenia] have collectively suggested that nicotine may be efficacious in remediating selected cognitive deficits associated with these disorders, thus providing a framework for understanding the specific vulnerability of these patients to smoking initiation and maintenance. However, the specific gain in cognitive performance produced by nicotine administration in healthy subjects with normal cognitive function is less clear. This article reviews our current understanding of central nicotinic acetylcholine receptor (nAChRs) systems in normal and neuropsychiatric disease states and, specifically, their role with respect to cognitive dysfunction and clinical symptoms in several specific neuropsychiatric populations, including ADHD, Alzheimer's disease, Parkinson's disease, Tourette's Disorder, schizophrenia and affective disorders. The potential benefits of nicotinic agents for therapeutic use in neuropsychiatric disorders is discussed, as well as directions for further research in this area.

Effect of repeated nicotine exposure on high-affinity nicotinic acetylcholine receptor density in spontaneously hypertensive rats

Spontaneously hypertensive rats (SHRs) are often used as a model of attention deficit hyperactivity disorder (ADHD) and to investigate the effects of hypertension on cognitive function. Further, they appear to have reduced numbers of central nicotinic acetylcholine receptors (nAChRs) and, therefore, may be useful to model certain aspects of Alzheimer's disease (AD) and other forms of dementia given that a decrease in nAChRs is thought to contribute to cognitive decline in these disorders. In the present study, based on reports that chronic nicotine exposure increases nAChRs in several mammalian models, we tested the hypothesis that repeated exposures to a relatively low dose of the alkaloid would ameliorate the receptor deficits in SHR. Thus, young-adult SHRs and age-matched Wistar-Kyoto (WKY) control rats were treated with either saline or nicotine twice a day for 14 days (total daily dose = 0.7 mg/kg nicotine base) and then sacrificed. Quantitative receptor autoradiography with [125I]-IPH, an epibatidine analog, revealed: (1) that high-affinity nAChRs were higher in saline-treated WKY (control) rats compared to saline-treated SHRs in 18 of the 19 brain region measured, although statistically different only in the mediodorsal thalamic nuclei, (2) that nicotine significantly increased nAChR binding in WKY rats in six brain areas including cortical regions and the anterior thalamic nucleus, (3) that there were no cases where nicotine significantly increased nAChR binding in SHRs. These results indicate that subjects deficient in nAChRs may be less sensitive to nAChR upregulation with nicotine than normal subjects and require higher doses or longer periods of exposure.

Nicotinic receptor mechanisms and cognition in normal states and neuropsychiatric disorders

Cigarette smoking rates in the American population are approximately 23%, whereas rates of smoking in clinical and population studies of individuals with neuropsychiatric disorders are typically two- to four-fold higher. Studies conducted in a variety of neuropsychiatric populations [e.g. attention-deficit hyperactivity disorder (ADHD), Alzheimer's disease, schizophrenia] have collectively suggested that nicotine may be efficacious in remediating selected cognitive deficits associated with these disorders, thus providing a framework for understanding the specific vulnerability of these patients to smoking initiation and maintenance. However, the specific gain in cognitive performance produced by nicotine administration in healthy subjects with normal cognitive function is less clear. This article reviews our current understanding of central nicotinic acetylcholine receptor (nAChRs) systems in normal and neuropsychiatric disease states and, specifically, their role with respect to cognitive dysfunction and clinical symptoms in several specific neuropsychiatric populations, including ADHD, Alzheimer's disease, Parkinson's disease, Tourette's Disorder, schizophrenia and affective disorders. The potential benefits of nicotinic agents for therapeutic use in neuropsychiatric disorders is discussed, as well as directions for further research in this area.

Alcohol and tobacco consumption as risk factors of dementia: a review of epidemiological studies

The association between dementia and smoking or alcohol use has been examined in several epidemiological studies. In many case-control studies, a decreased risk of dementia or Alzheimer's disease (AD) was observed among smokers. However, when this association was analysed in prospective studies, an increased risk of AD was observed. In addition, in the PAQUID study, we showed that the decreased risk disappeared after adjustment for educational level and occupation. These factors are strong confounders in the association between dementia and tobacco use. We also showed that moderate consumption of wine was associated with a lower risk of developing AD. This result remains unchanged after adjustment for many potential confounders. The association between moderate alcohol consumption and risk of developing a dementia or AD was recently confirmed by prospective studies. In some studies, wine consumption was more specifically associated with a decreased risk, whereas beer or spirit consumption was not associated. These results suggest that tobacco consumption is not associated with a lower risk of dementia and that moderate alcohol intake does not increase the risk of developing dementia.

Head injury as a risk factor for Alzheimer's disease: the evidence 10 years on; a partial replication

OBJECTIVE

To determine, using a systematic review of case-control studies, whether head injury is a significant risk factor for Alzheimer's disease. We sought to replicate the findings of the meta-analysis of Mortimer et al (1991).

METHODS

A predefined inclusion criterion specified case-control studies eligible for inclusion. A comprehensive and systematic search of various electronic databases, up to August 2001, was undertaken. Two independent reviewers screened studies for eligibility. Fifteen case-control studies were identified that met the inclusion criteria, of which seven postdated the study of Mortimer et al.

RESULTS

We partially replicated the results of Mortimer et al. The meta-analysis of the seven studies conducted since 1991 did not reach significance. However, analysis of all 15 case-control studies was significant (OR 1.58, 95% CI 1.21 to 2.06), indicating an excess history of head injury in those with Alzheimer's disease. The finding of Mortimer et al that head injury is a risk factor for Alzheimer's disease only in males was replicated. The excess risk of head injury in those with Alzheimer's disease is only found in males (males: OR 2.29, 95% CI 1.47 to 2.06; females: OR 0.91, 95% CI 0.56 to 1.47).

CONCLUSIONS

This study provides support for an association between a history of previous head injury and the risk of developing Alzheimer's disease.

Smoking as a risk factor for Alzheimer's disease: contrasting evidence from a systematic review of case-control and cohort studies

AIMS

To investigate the risk of Alzheimer's disease (AD) associated with smoking.

DESIGN

Meta-analyses of case-control and cohort studies.

DATA SOURCE

Index Medicus-Medline (1966-April 2000) and PsycINFO (1984-April 2000) databases were systematically consulted for the retrieval of references. This search was supplemented by manual search of relevant references quoted by other studies and reviews.

STUDY SELECTION

Irrelevant abstracts and articles were identified by one of the authors. These papers were retrieved and examined by at least two of the authors, who initially assessed them for the relevance of the exposure (smoking), outcome (AD) and study-design (case-control or cohort study).

DATA EXTRACTION

Two reviewers rated independently the quality of selected papers. Whenever possible, raw data were extracted and the crude odds ratio (OR) calculated using the Cornfield method. The pooled risk ratios were estimated using a fixed-effects model.

FINDINGS

Twenty-one case-control studies reported data on 5323 subjects. The estimated pooled odds ratio (OR) was 0.74 [95% confidence interval (CI) = 0.66-0.84]. In another analysis incorporating ORs adjusted for confounding variables (such as age, sex, schooling and alcohol use), the pooled odds ratio was 0.82 (95% CI = 0.70-0.97). Finally, in a analysis that included only the four case-control studies that used matched design the pooled odds ratio was 0.82 (95% CI = 0.53-1.27). Eight cohort studies reported data on 43 885 people at risk-the overall relative risk (RR) of AD among ever smokers was 1.10 (95% CI = 0.94-1.29). Restricting the analysis to the two cohort studies that described the number of subjects who were smokers at baseline and later developed AD produced a RR of 1.99 (95% CI = 1.33-2.98).

CONCLUSIONS

Case-control and cohort studies produce conflicting results as to the direction of the association between smoking and AD. Survival bias and other methodological problems associated with case-control studies may partly explain this difference. Access to information collected by ongoing follow-up studies may contribute to clarify the role of smoking in AD. If new results confirm that smoking is associated with increased risk of AD, then smoking prevention and cessation should become public health priorities in the fight against dementia.

Risk factors for Alzheimer's disease: a population-based, longitudinal study in Manitoba, Canada

BACKGROUND

Current knowledge of risk factors for Alzheimer's disease (AD) is limited. Data from a longitudinal, population-based study of dementia in Manitoba, Canada were used to investigate risk factors for AD.

METHODS

Cognitively intact subjects completed a risk factor questionnaire assessing sociodemographic, genetic, environmental, medical and lifestyle exposures. Five years later, 36 subjects had developed AD and 658 remained cognitively intact.

RESULTS

Older subjects or those who had fewer years of education were at greater risk of AD. After adjusting for age, education and sex, occupational exposure to fumigants/ defoliants was a significant risk factor for AD (relative risk [RR] = 4.35; 95% CI : 1.05--17.90). A history of migraines increased the risk of AD (RR = 3.49; 95% CI : 1.39--8.77); an even stronger effect was noted among women. Self-reported memory loss at baseline was associated with subsequent development of AD (RR = 5.15; 95% CI : 2.36--11.27). Vaccinations and occupational exposure to excessive noise reduced the risk of AD.

CONCLUSIONS

Some well-known risk factors for AD were confirmed in this study and potential new risk factors were identified. The association of AD with a history of migraines and occupational exposure to defoliants/fumigants is of particular interest because these are biologically plausible risk factors.

Effects of combined exposure to aluminium and ethanol on food intake, motor behaviour and a few biochemical parameters in pubertal rats

Combined daily administration of aluminium chloride (260 mg/kg, oral) and ethanol (2 g/kg, oral), to pubertal male rats for 30 days was found to significantly decrease food intake, body weight gain and serum protein levels. Spontaneous motor activity and rota-rod motor coordination were also significantly impaired. Acetylcholinesterase activity was significantly diminished in the cerebrum and cerebellum. The results obtained in the present study are suggestive of a potentiation of cholinotoxic effects of the two compounds when administered together. Thus, when combined, ethanol may increase pubertal rat's susceptibility to the toxic effects of aluminium.

Is smoking associated with the risk of developing Alzheimer's disease? Results from three Canadian data sets

PURPOSE

To determine whether smoking is associated with Alzheimer's disease (AD).

METHODS

Analyses were conducted using three Canadian data sets: the University of Western Ontario Dementia Study (200 cases, 163 controls), the Canadian Study of Health and Aging (258 cases, 258 controls), and the patient database from the Clinic for Alzheimer Disease and Related Disorders at the Vancouver Hospital and Health Sciences Centre (566 cases, 277 controls). The association between smoking and AD was investigated using bivariate analyses and multiple logistic regression models adjusted for the potential confounders age, sex, educational level, family history of dementia, head injury, and hypertension.

RESULTS

The results of bivariate analyses were inconsistent across the three data sets, with smoking status a significant protective factor, a significant risk factor, or not associated with AD. The results of multiple logistic regression models, however, were consistent: any association between smoking status and AD disappeared in all three data sets after adjustment for confounders.

CONCLUSIONS

Smoking status was consistently not associated with AD across all three data sets after adjustment for confounders. Failure to adjust for relevant confounders may explain inconsistent reports of the influence of smoking on AD. Any protective effect of smoking may be limited to specific AD subtypes (e.g., early onset AD).

Does an interaction between smoking and drinking influence the risk of Alzheimer's disease? Results from three Canadian data sets

Investigation of the relationship of smoking and drinking to Alzheimer's disease (AD) may advance research on the cause of AD and provide a basis for treatment. Pharmacological mechanisms for an involvement of smoking and drinking are plausible but epidemiologic reports are inconsistent. Evidence of behavioural and physiological interactions suggests that tobacco and alcohol use may not only individually affect AD, but may also modify each other's effects. A modelling strategy was developed to examine the interaction between smoking and drinking on the risk of AD. Three Canadian data sets were analysed: the University of Western Ontario Dementia Study (UWODS) (n=363); the Canadian Study of Health and Aging (CSHA) (n=516), and the database from the Clinic for Alzheimer Disease and Related Disorders at the Vancouver Hospital and Health Sciences Centre, University of British Columbia site (UBC) (n=843). Multiple logistic regression models were adjusted for the potential confounders age, age squared, sex, education, family history of dementia, head injury and hypertension. Analysis of the CSHA provided evidence consistent with the hypothesis that smoking and drinking influence each other's effects on AD, with smoking reducing the risk of AD among drinkers. A similar interaction was marginally significant (p=0.052) in the UWODS data set, but not significant in the UBC data. Extension of these analyses, particularly in longitudinal studies and within genetic risk groups, is needed to determine whether this interaction can be replicated. If so, research on the biological interactions of nicotine and alcohol may provide a basis for the development of therapeutic interventions as well as providing clues to the cause of this disorder.

A unifying hypothesis of Alzheimer's disease. III. Risk factors

Normal ageing and Alzheimer's disease (AD) have many features in common and, in many respects, both conditions only differ by quantitative criteria. A variety of genetic, medical and environmental factors modulate the ageing-related processes leading the brain into the devastation of AD. In accordance with the concept that AD is a metabolic disease, these risk factors deteriorate the homeostasis of the Ca(2+)-energy-redox triangle and disrupt the cerebral reserve capacity under metabolic stress. The major genetic risk factors (APP and presenilin mutations, Down's syndrome, apolipoprotein E4) are associated with a compromise of the homeostatic triangle. The pathophysiological processes leading to this vulnerability remain elusive at present, while mitochondrial mutations can be plausibly integrated into the metabolic scenario. The metabolic leitmotif is particularly evident with medical risk factors which are associated with an impaired cerebral perfusion, such as cerebrovascular diseases including stroke, cardiovascular diseases, hypo- and hypertension. Traumatic brain injury represents another example due to the persistent metabolic stress following the acute event. Thyroid diseases have detrimental sequela for cerebral metabolism as well. Furthermore, major depression and presumably chronic stress endanger susceptible brain areas mediated by a host of hormonal imbalances, particularly the HPA-axis dysregulation. Sociocultural and lifestyle factors like education, physical activity, diet and smoking may also modulate the individual risk affecting both reserve capacity and vulnerability. The pathophysiological relevance of trace metals, including aluminum and iron, is highly controversial; at any rate, they may adversely affect cellular defences, antioxidant competence in particular. The relative contribution of these factors, however, is as individual as the pattern of the factors. In familial AD, the genetic factors clearly drive the sequence of events. A strong interaction of fat metabolism and apoE polymorphism is suggested by intercultural epidemiological findings. In cultures, less plagued by the 'blessings' of the 'cafeteria diet-sedentary' Western lifestyle, apoE4 appears to be not a risk factor for AD. This intriguing evidence suggests that, analogous to cardiovascular diseases, apoE4 requires a hyperlipidaemic lifestyle to manifest as AD risk factor. Overall, the etiology of AD is a key paradigm for a gene-environment interaction. Copyright 2000 John Wiley & Sons, Ltd.

Depressive disorders in Chinese patients with Alzheimer's disease

OBJECTIVE

The present study was to investigate the prevalence and potential risk factors of depressive disorders in Chinese patients with Alzheimer's disease (AD).

METHOD

A series of consecutive AD patients from the Memory Disorders Clinic of the Veterans General Hospital, Taipei were studied. Psychiatric diagnosis was made according to DSM-III-R criteria with the use of the Structured Clinical Interview for DSM-III-R (SCID). The Chinese version of the Cognitive Abilities Screening Instrument (CASI) and the Hamilton Depression Rating Scale (HDRS) were also applied. Primary caregivers were interviewed for the Clinical Dementia Rating (CDR) scale, the Barthel Index and the Alzheimer's Deficit Scale (ADS).

RESULTS

Among 141 AD patients, seven (5.0%) were diagnosed with major depression, 11 (7.8%) with dysthymia and five (3.5%) with depressive disorder not otherwise specified. Women were at elevated risk for depressive disorders and had more severe symptoms of depression.

CONCLUSIONS

The prevalence of depressive disorders among Chinese AD patients is in the middle of the range of western findings. The risk factor for depression is female gender.