Risk factors for clinically diagnosed Alzheimer's disease: a case-control study of an Italian population

Asthma, eczema, rhinitis and the risk for dementia

BACKGROUND

Inflammation is associated with Alzheimer's disease (AD) and dementia. In light of the chronic inflammatory properties of the atopic disorders asthma, eczema and rhinitis, we hypothesized an association with dementia.

METHODS

Self-reported asthma, eczema or rhinitis was assessed (prior to dementia follow-up) through questionnaires in the 1960s or 1970s in twins from the population-based Swedish Twin Registry. Dementia was assessed both longitudinally (n = 22,188), through linkages to two population-based registers, and cross-sectionally (n = 7,800), through telephone cognitive screening followed by a clinical evaluation of suspects of dementia. Risk ratios were estimated with Cox and logistic regression models controlling for vascular disease and genetic confounding.

RESULTS

In the longitudinal study, a history of atopy was positively associated with dementia (HR = 1.16; 1.01-1.33). In the cross-sectional study we found overall lower risks, none of which was statistically significant. Asthma was associated with a shorter survival time following AD onset.

CONCLUSIONS

Atopy is associated with a modestly increased risk of AD and dementia that is not mediated by vascular disease or due to genetic confounding. A history of asthma is associated with shorter life expectancy after AD diagnosis.

Lifestyle-related factors in predementia and dementia syndromes

Cognitive decline and dementia have a deep impact on the health and quality of life of older subjects and their caregivers. Since the therapeutic options currently available have demonstrated limited efficacy, the search for preventive strategies for cognitive decline and dementia are mandatory. A possible role of lifestyle-related factors was recently proposed for age-related changes of cognitive function, predementia syndromes and the cognitive decline of degenerative (Alzheimer's disease [AD]) or vascular origin. At present, cumulative evidence suggests that vascular risk factors may be important in the development of mild cognitive impairment (MCI), dementia and AD. Moderate alcohol drinking has been proposed as a protective factor against MCI and dementia in several longitudinal studies, but contrasting findings also exist. The Mediterranean diet could therefore be an interesting model with which to further study the association between dietary patterns and cognitive functioning, given the suggested role of many components of this diet (monounsaturated fatty acids, polyunsaturated fatty acids, cereals and red wine) in contrasting cognitive impairment and dementia. The association between low education and predementia and dementia syndromes is supported by the majority of studies, but very few studies have investigated whether this association may be attributed with lifestyle factors that covary with education. Studies in the literature seem to identify in physical exercise one promising strategy in decreasing cognitive decline, but some of the limitations of these studies do not allow us to draw definite conclusions. At present, in older subjects, healthy diets, antioxidant supplements, the prevention of nutritional deficiencies, and moderate physical activity could be considered the first line of defense against the development and progression of predementia and dementia syndromes. However, in most cases, these were only observational studies, and results are awaited from large multicenter randomized clinical trials in older persons that may clarify the possible synergy, for example, between moderate exercise, physical activity and healthy Mediterranean diet on cognition in the elderly.

Down’s syndrome and Alzheimer’s disease: two sides of the same coin

All Down’s syndrome individuals develop Alzheimer’s disease (AD) neuropathology by the age of 40 years. To unite the two diseases under one hypothesis, we have suggested that classical AD, both of the genetic and late-onset sporadic forms, might be promoted by small numbers of trisomy 21 cells developing during the life of the affected individual. Recent evidence from several laboratories will be presented, which strongly supports the trisomy 21 hypothesis that defects in mitosis, and particularly in chromosome segregation, may be a part of the AD process. Specifically, genetic mutations that cause familial AD disrupt the cell cycle and lead to chromosome aneuploidy, including trisomy 21, in transgenic mice and transfected cells; cells from both familial and sporadic AD patients exhibit chromosome aneuploidy, including trisomy 21. The possibility that many cases of AD are mosaic for trisomy 21 suggests novel approaches to diagnosis and therapy.

Do work-related stress and reactivity to stress predict dementia more than 30 years later?

The purpose of this study was to examine associations for work-related stress, reactivity to stress, and subsequent risk of dementia. The sample consisted of members of the population-based Swedish Twin Registry who were participants in the HARMONY study (n=2,049). We used case control and cotwin control designs, with information on work-related stress and reactivity to stress collected as part of a questionnaire completed in 1967. Dementia was diagnosed approximately 30 years later using a 2-stage procedure-screening for cognitive impairment followed by full clinical evaluation. We found that measures of work-related stress (job dissatisfaction and high job demands) were not associated with dementia risk. Greater reactivity to stress predicted higher risk of dementia controlling for age, education, sex, occupational status, alcohol use, and smoking status (odds ratio=1.57, 95% confidence interval 1.08-2.31). Cotwin control analyses also showed that dementia probands were more likely to report high reactivity to stress than their nondemented cotwins. We did not find evidence of an interaction between work stress and reactivity in predicting dementia. Overall, indicators of stress due to environment (ie, work) were not associated with dementia, whereas the individual characteristic of reactivity to stress predicted dementia risk.

The epidemiology of Alzheimer's disease in relation to aluminium

The combination of an ageing population, an exponential increase in the incidence of dementing illness with age, and the high demands that demented patients place on health care resources makes Alzheimer's disease a major public health issue. So far, epidemiologists have made better progress in quantifying the frequency of the disease than in identifying strong risk factors, but evidence is accumulating to implicate environmental exposure to aluminium in the aetiology. The finding of a geographical correlation between death rates from dementia and water aluminium concentrations in Norway has since been replicated in several other surveys. Although ecological studies of this type should be interpreted cautiously, the association between Alzheimer's disease and aluminium in drinking water may prove to be an example of a potentially important biological effect of aluminium.

Anesthesia leads to tau hyperphosphorylation through inhibition of phosphatase activity by hypothermia

Postoperative cognitive dysfunction, confusion, and delirium are common after general anesthesia in the elderly, with symptoms persisting for months or years in some patients. Even middle-aged patients are likely to have postoperative cognitive dysfunction for months after surgery, and Alzheimer's disease (AD) patients appear to be particularly at risk of deterioration after anesthesia. Several investigators have thus examined whether general anesthesia is associated with AD, with some studies suggesting that exposure to anesthetics may increase the risk of AD. However, little is known on the biochemical consequences of anesthesia on pathogenic pathways in vivo. Here, we investigated the effect of anesthesia on tau phosphorylation and amyloid precursor protein (APP) metabolism in mouse brain. We found that, regardless of the anesthetic used, anesthesia induced rapid and massive hyperphosphorylation of tau, rapid and prolonged hypothermia, inhibition of Ser/Thr PP2A (protein phosphatase 2A), but no changes in APP metabolism or Abeta (beta-amyloid peptide) accumulation. Reestablishing normothermia during anesthesia completely rescued tau phosphorylation to normal levels. Our results indicate that changes in tau phosphorylation were not a result of anesthesia per se, but a consequence of anesthesia-induced hypothermia, which led to inhibition of phosphatase activity and subsequent hyperphosphorylation of tau. These findings call for careful monitoring of core temperature during anesthesia in laboratory animals to avoid artifactual elevation of protein phosphorylation. Furthermore, a thorough examination of the effect of anesthesia-induced hypothermia on the risk and progression of AD is warranted.

Medications and diet: protective factors for AD?

In the past decade, studies of Alzheimer disease risk and medication exposures, supplement intake, and dietary factors have grown in number. Typically identified in case-control and cross-sectional studies, many of these exposures have also been replicated in prospective studies. These observational studies have provided the foundation for the development of several prevention trials. This brief review focuses on exposures that have been identified in multiple studies. Observational studies of medications suggesting protection for Alzheimer disease include estrogen hormonal therapy, nonsteroidal anti-inflammatory drugs, and cholesterol-lowering statins. Evidence regarding dietary and supplemental intake of vitamins E, C, and folate, and studies of alcohol and wine intake are also reviewed. At present, there is insufficient evidence to make public health recommendations, but these studies can provide potentially important clues and new avenues for clinical and laboratory research.

Tools of the Epidemiologist

This review provides a summary of epidemiologic tools to facilitate understanding of the design and analysis of studies of Alzheimer disease (AD) and related disorders. Proportions, ratios, rates, prevalence, incidence, study designs, bias, confounding, effect modification, odds and risk ratios, statistical power, and confidence intervals are defined and discussed. Descriptive epidemiology is concerned with describing the distribution of disease by person, place, and time. It is useful for hypothesis generation, but not generally for hypothesis testing. Observational analytic epidemiology focuses on identifying putative causes for an illness. Although its primary mission is hypothesis testing, it can lead to new hypotheses as well. Finally, experimental analytic epidemiology or clinical trials can provide rigorous tests of presumed causal associations. The strengths and limitations of various designs as they apply to determining causal associations in studies of AD and dementia are reviewed. Over the past 60 years, the epidemiologic study of dementia has evolved from basic descriptive studies of prevalence and incidence to case-control and cohort studies and finally to the first clinical trials to prevent AD.

Genetic study of Sardinian patients with Alzheimer's disease

We describe the genetic analysis of an Alzheimer's disease (AD) sample derived from a genetically isolated population. Genetic assessment included the analysis of genes involved in AD, such as the genes for amyloid precursor protein (APP), presenilin 1 (PSEN1) and presenilin 2 (PSEN2). We also assessed genes for some proteins that constitute the gamma-secretase complex: nicastrin (NCSTN), presenilin enhancer-2 (PEN2), in addition to the AD risk factor apolipoprotein E (APOE). Using polymerase chain reaction and single strand conformational polymorphism method, screens for APP, PSEN1 and PSEN2 genes revealed one mutation in PSEN1. Furthermore, we found an intronic +17G>C polymorphism in PEN2 which, in homozygous form, was greater in early onset Alzheimer's disease (EOAD) compared to controls, and one haplotype in the NCSTN gene which was linked to EOAD and familial AD (FAD). Finally, the genotyping of APOE confirmed that the varepsilon4 allele could be a risk factor for the onset of AD, in particular for FAD subjects. In conclusion, these results show the existence of Sardinian genetic peculiarities, essential in studies regarding genetically inherited and multifactorial disorders, as AD.

Estrogen-containing hormone therapy and Alzheimer’s disease risk: Understanding discrepant inferences from observational and experimental research

Estrogen has the potential to influence brain processes implicated in Alzheimer's disease pathogenesis. With the loss of ovarian estrogen production after menopause, estrogen-containing hormone therapy might be expected to influence the risk of Alzheimer's disease. Observational data link use of hormone therapy to reductions in Alzheimer risk, but experimental evidence from the Women's Health Initiative Memory Study trial demonstrates that oral estrogen, with or without a progestin, increases the incidence of dementia for postmenopausal women age 65 years or older. Mechanisms of harm in this setting are unknown. Bias and unrecognized confounding in observational research are leading candidates for discrepant results between observational studies and the Women's Health Initiative Memory Study trial. Studies are also distinguished by differences in outcome measures, hormone therapy formulations, prevalence of menopausal symptoms among study participants, and participant age. Finally, Women's Health Initiative Memory Study findings may not generalize to estrogen use by relatively young women during the menopausal transition or early postmenopause, a class of women who were ineligible for the Women's Health Initiative Memory Study trial. In observational studies, hormone therapy exposure often included use by younger women for menopausal vasomotor symptoms. Although there is no clinical trial evidence that hormone therapy at any age protects against Alzheimer's disease, it remains to be determined whether the age at which hormone exposure occurs or the timing of hormone therapy initiation in relation to the menopause (the critical window hypothesis) modifies treatment outcomes on dementia risk.

Hormone replacement therapy and cognitive performance in postmenopausal women—a review by cognitive domain

Laboratory, animal and neuroimaging evidences suggest that hormone replacement therapy (HRT) may be beneficial to human cognition. This systematic review includes 26 studies on the association between HRT and cognition and 17 studies on HRT and risk of dementia. It was hypothesised that HRT would have a positive association with cognitive speed and verbal memory and possibly visual memory but not with executive functioning, and would be associated with a decreased risk of dementia. Evidence for HRT's neuroenhancing and neuroprotective properties was also evaluated. There was significant statistical and clinical heterogeneity among studies precluding meta-analysis. Results showed no consistent relationship between HRT and performance in any cognitive domain. Cross-sectional studies tended to report more positive results than longitudinal studies and randomised-controlled trials, particularly in the areas of verbal memory and executive functioning. HRT was associated with decreased risk of dementia in observational studies, but with increased risk in one randomised-controlled trial. Cognitive improvement or maintenance are not secondary benefits of HRT.

Endogenous and exogenous hormone exposure and risk of cognitive impairment in Swedish twins: a preliminary study

PURPOSE

To analyze the risk of cognitive impairment among female Swedish Twins with regard to endogenous and exogenous hormone exposure.

DESIGN AND SETTING

A cross-sectional analysis of data from the HARMONY Study, a population-based cohort study of cognitive impairment in the Swedish Twin Registry.

METHODS

Information regarding age at menarche and menopause, parity, and length and type of hormone therapy (HT) was collected via a telephone interview from 6604 women, aged 65-84. Cognitive impairment was assessed with the TELE, a brief telephone cognitive screen.

RESULTS

Length of reproductive period was inversely associated with risk of cognitive impairment (p<0.01). The OR was 1.15 (CI 95% 0.96-1.36) for women with reproductive periods <35 years and 0.82 (CI 95% 0.66-1.00) for women with reproductive periods >39 years. Age at menopause was inversely associated with risk of cognitive impairment. Use of HT was associated with average 40% decline in the risk of cognitive impairment, independent of type and timing of treatment.

CONCLUSION

Our results suggest that both increased length of reproductive period and HT are associated with reduced risk of cognitive impairment.

Sex, Hormones, and Alzheimer's Disease

More women than men have Alzheimer's disease (AD). Retrospective studies suggested that hormone replacement therapy (HRT) might counteract this disparity by reducing the risk of developing dementia. However, a recent, large, prospective study revealed the puzzling result that HRT increased dementia risk. A review of the literature was conducted to generate hypotheses that might explain why more women than men have AD, and how HRT may increase dementia risk. Longer life span of women than men may be the largest factor in the preponderance of women with AD. Longer duration of disease, less vascular dementia, and less testosterone in women than men may also contribute somewhat. HRT might increase dementia risk by several mechanisms: greater risk of strokes, leading to dementia; use of medroxyprogesterone acetate and estrone, which might have somewhat different possible effects on neuronal and cerebrovascular function than may progesterone and estradiol; decrease of free testosterone which might protect against AD; a dose or delivery method perhaps producing drug levels that might lie outside a hypothetical beneficial range; and down-regulation of estrogen receptors on cholinergic neurons, possibly reducing cholinergic activity. Further study is required to discern by which of several possible mechanisms HRT increases dementia risk.

Fall-related brain injuries and the risk of dementia in elderly people: a population-based study

Severe head injury in early adulthood may increase the risk of dementia in older age, but it is not known whether head injury in later life also increases the risk of dementia. A representative sample (82%) of persons aged 70 years or older with a Mini-Mental State Examination (MMSE) test score of > or =26 (n = 325) were followed-up for 9 years to record all their fall-related head injuries resulting in traumatic brain injury (TBI). At the end of the follow-up period, 152 persons (81% of the surviving population) were examined for clinical dementia, according to DSM-IV criteria. Eight persons sustained a TBI and 34 developed dementia. Brain injury was associated with younger age at detection of dementia even when adjusted for sex and educational status (low educational status significantly associated with dementia); age-specific hazard ratio (95% confidence interval) 2.80 (1.35-5.81). In a population scoring > or =28 points in the baseline MMSE an apolipoprotein E (ApoE) epsilon4 phenotype was also associated with younger age at the time of detecting dementia; 3.56 (1.35-9.34), and the effect of brain injury and ApoE epsilon4 phenotype was synergistic; 7.68 (2.32-25.3). We conclude that fall-related TBI predicts earlier onset of dementia and the effect is especially high amongst subjects who carry the ApoE epsilon4 allele.

Estrogen replacement therapy, Alzheimer's disease, and mild cognitive impairment

This article highlights the latest findings regarding estrogen replacement therapy in the treatment and prevention of Alzheimer's disease (AD) and mild cognitive impairment in women. Despite considerable evidence from observational studies, recent randomized clinical trials of conjugated equine estrogens, alone and in combination with progestin, have shown no benefit for either the treatment of established AD or for the short-term prevention of AD, mild cognitive impairment, or cognitive decline. Based on the evidence, there is no role at present for estrogen replacement therapy in the treatment or prevention of AD or cognitive decline, despite intriguing results from the laboratory and from observational studies. However, numerous questions remain about the biologic effects of estrogens on brain structure and function. Additional basic and clinical investigations are necessary to examine different forms and dosages of estrogens, other populations, and the relevance of timing and duration of exposure.

Estrogen- and tamoxifen-associated effects on brain structure and function

We evaluated the effects of estrogen and tamoxifen, a selective estrogen receptor modulator, on positron emission tomography (PET) measures of brain glucose metabolism and magnetic resonance imaging (MRI) measures of hippocampal atrophy. Three groups of postmenopausal women were studied, women taking estrogen (ERT+), women with breast cancer taking tamoxifen (TAM), and women not taking estrogen or tamoxifen (ERT-). All subjects received a PET scan, an MRI scan, and cognitive testing. The TAM group showed widespread areas of hypometabolism in the inferior and dorsal lateral frontal lobes relative to the other two groups. The ERT- group showed lower metabolism in the inferior frontal cortex and temporal cortex with respect to the ERT+ group. The TAM group also showed significantly lower semantic memory scores than the other two groups. Finally, the TAM group had smaller right hippocampal volumes than the ERT+ group, an effect that was of borderline significance. Both right and left hippocampal volumes were significantly smaller than the ERT+ group when a single outlier was removed. The ERT- group had hippocampal volumes that were intermediate to the other two groups. These findings provide physiological and anatomical evidence for neuroprotective effects of estrogen.

In vivo effects of estrogen on human brain

Age-related brain disorders such as Alzheimer's disease (AD) are becoming increasingly prevalent. Estrogen replacement therapy (ERT) has shown potential both as a preventive measure and treatment for such disorders. Good evidence from basic science demonstrates that estrogen has multiple protective effects on neurons and neurotransmitter systems, and the effects of ERT can be demonstrated on the human brain using techniques such as functional neuroimaging. However, the evidence for estrogen's having a clinical role in the treatment and prevention of neuropsychiatric disorders is not well established. In this article we review research into the effects of estrogen on the human brain and we consider the role for ERT as a therapeutic tool.

Nicastrin gene in familial and sporadic Alzheimer's disease

Nicastrin is a protein recently discovered associated to presenilins and involved in the production of amyloid beta peptide that accumulates in Alzheimer's disease (AD) brain. In this study the nicastrin gene was examined for unknown mutations and polymorphisms in 104 patients with familial AD (52 early-onset and 52 late-onset), 174 sporadic AD and 191 healthy neurological controls of Italian origin. The scanning of the nicastrin gene identified a missense mutation (N417Y) in two patients with sporadic AD, in an early-onset familial AD and in a young control subject. Furthermore, we found two silent mutations and four intronic polymorphisms, three of them co-segregating in a single haplotype. We found some differences in the distribution of genotype alterations in the AD population compared to the controls. However, our data together with other evidence did not support the pathological role of missense mutation N417Y.

Preliminary evidence that estrogen protects against age-related hippocampal atrophy

Few studies have examined gender differences in hippocampal volumes, and the potential effect of estrogen on these measures has not been well studied. We used MRI to measure hippocampal volumes in elderly Mexican American men and women subjects in order to determine if there were gender differences and if estrogen replacement therapy (ERT) had an effect on hippocampal volume in postmenopausal women. MRI measures of hippocampal volumes (normalized to intracranial volume) were compared in 59 women and 38 men. Further comparisons were made between men subjects, women subjects taking ERT, and women subjects not taking ERT. There were no significant effects of gender on normalized hippocampal volumes. However, women subjects taking ERT had larger right hippocampal volumes than women subjects not taking ERT and larger anterior hippocampal volumes than men subjects and women subjects not taking ERT. These findings suggest a neuroprotective effect of estrogen.

Are tobacco and alcohol use related to Alzheimer's disease? A critical assessment of the evidence and its implications

Elucidation of the association of tobacco and alcohol use with Alzheimer's disease (AD) may advance etiological hypotheses and provide a theoretical basis for treatment. There is currently no cure or effective treatment for AD, and no cause has been established. Pharmacological evidence supports a plausible biological mechanism for the involvement of tobacco use: nicotine compensates for some of the cholinergic deficits observed in AD. Epidemiological evidence, however, is inconsistent, although recent meta-analyses also support a protective effect. Although smoking per se is certainly not advocated, further investigation of a potential protective effect of nicotine on AD is warranted. Pharmacological studies implicate alcohol use as a possible risk factor for AD; the epidemiological studies are again inconclusive. Alcohol consumption is associated with daily smoking and smokers are, in turn, more likely to consume alcohol. Since tobacco use may decrease the risk of developing AD and alcohol use may increase it, it is important to consider these two substances together: the effect of one may negate the other. This literature review critically evaluates the evidence for an association of tobacco and alcohol use with AD and identifies key issues for further research.

Nonsteroidal anti-inflammatory drug use and the risk for Alzheimer's disease: dissecting the epidemiological evidence

Inflammation is hypothesised to contribute to the genesis of pathology causing or contributing to Alzheimer's disease (AD). As a part of the immune response in the brain, the prostaglandin pathway is induced; this pathway is the target for NSAIDs, the most widely used anti-inflammatory medication. There are many epidemiological studies, which are reviewed here, suggesting NSAIDs reduce the risk for AD. The most recent of these studies suggest NSAIDs should be taken for at least 2 years. There are little data in humans about whether one type of NSAID is more effective than another. To date, randomised, double-blind, clinical trials in patients with AD have been negative. There is one prevention trial that will yield valuable information about the efficacy of NSAIDs in slowing down the progression of, or preventing, AD. At present, no recommendations can be made concerning the when, what, who and for how long a person should take an NSAID to reduce his or her risk for AD.

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.

Estrogen and cognitive functioning in women

Research in basic neuroscience has provided biological plausibility for the hypothesis that estrogen replacement therapy (ERT) would protect against cognitive aging in healthy women. The weight of the evidence from randomized controlled trials of estrogen and cognition in women shows that this hormone preferentially protects verbal memory in postmenopausal women, whereas findings from observational studies are less consistent and show a more diffuse effect of estrogen on a range of cognitive functions. There is fairly consistent evidence from epidemiological studies that ERT significantly reduces the risk of Alzheimer's disease (AD) in women. On the other hand, findings from controlled treatment trials of women diagnosed with probable AD failed to show that physiological doses of ERT ameliorate existing deficits in cognitive functioning and/or prevent further deterioration in memory that inevitably occurs in these women over time. Finally, an accumulating body of evidence is beginning to suggest that the immediate postmenopausal period may constitute a critical window for treatment with ERT that maximizes its potential to protect against cognitive decline with aging and/or to reduce the risk of AD.

The menopause and HRT. HRT and cognitive decline

It is biologically plausible that hormone replacement therapy (HRT) would be protective against cognitive decline and Alzheimer's disease (AD). We review observational and randomized trials to determine whether HRT might protect against cognitive decline in cognitively unimpaired and demented women. We also address issues of clinical relevance, including duration and type of treatment and patient characteristics, including type of menopause (surgical versus natural), age, education and menopausal symptoms. Differences in participant characteristics and testing methods limit the ability to draw conclusions across randomized studies of HRT in non-demented women. The available evidence suggests no detrimental effect of HRT on cognitive function and inconsistent benefits on verbal memory and reasoning, frontal functions and speeded attention. Meta-analyses of observational trials suggest that HRT protects against the development of AD, but randomized trials indicate no long-lasting benefit in patients with AD. Evidence is insufficient to recommend HRT to maintain cognitive function.

Alcohol consumption and incidence of dementia in a community sample aged 75 years and older

To explore the relationship between light to moderate alcohol consumption and risk of dementia and Alzheimer's disease in very old people, a community-based dementia-free cohort (n = 402) was followed for almost 6 years to detect incident dementia using the Diagnostic and Statistical Manual of Mental Disorders, 3rd Edition-Revised criteria. Data from the entire cohort and a subpopulation of those with baseline Mini-Mental State Examination score > or =24 (n = 317) were analyzed with Cox models. In the entire population, light to moderate drinking was significantly associated with a decreased risk of incident dementia and Alzheimer's disease compared with nondrinking (adjusted relative risk 0.5, 95% confidence interval 0.3 to 0.7). In the analysis of the subpopulation, however, the inverse association between light to moderate drinking and risk of incident dementia and Alzheimer's disease was less evident and no longer statistically significant. This study suggested that light to moderate alcohol drinking might protect against dementia and Alzheimer's disease among old people, although the possibility that such an association may be due to information bias cannot be totally ruled out.

Cognitive decline among female estrogen users in nursing homes

BACKGROUND

Clinical and epidemiological research has been done regarding the potential therapeutic benefit of estrogen in outpatients with and without dementia; however, the effects of estrogen therapy on cognition in elderly nursing home patients have not been previously examined.

METHODS

This retrospective cohort study compared 191 women estrogen users with 663 women nonestrogen users, matched according to age, nursing home facility, year of assessment, and baseline level of cognitive function. The outcome was decline in cognition, measured by the Cognitive Performance Scale, over a minimum follow-up period of 6 months.

RESULTS

No significant difference was found in the rate of cognitive decline among estrogen users and nonusers.

CONCLUSIONS

Estrogen therapy administered to nursing home residents is not associated with a reduction in cognitive decline. This study lends further support to recent controlled clinical trials that found no benefit for estrogen treatment on cognition in outpatients with dementia.

The health-related effects of alcohol use in older persons: a systematic review

Increased alcohol consumption is associated with substantial morbidity and mortality in young and middle-aged adult populations, but its effects on the health of older adults have received less attention. The objective of the study was to review published studies that assessed the effects of alcohol on falls or fall injuries, functional impairment, cognitive impairment, and all-cause mortality among older adults. MEDLINE database and bibliographies of selected citations were searched for English language studies published between 1966 and 1998 that examined the relationship between alcohol and one or more of the above outcomes. Also a study was analyzed if it included participants 60 years of age or older, or a broader age range of participants and reported results for older subgroups, or predominantly older participants as evidenced by a mean age of 65 years of age or above. Information on studies' sample sizes, exposure and outcome measures, and risk estimates were extracted, and articles were evaluated for methodologic quality using predetermined criteria. Eighty-four studies were identified that examined 91 potential exposure-outcome associations including falls or fall injuries (n = 26); functional impairment (n = 13); cognitive impairment (n = 32); and all-cause mortality (n = 20). The percentage of studies demonstrating harm, no association, or benefit by outcome included falls (15% vs. 81% vs. 4%); functional disability (38% vs. 46% vs. 16%); cognitive impairment (31% vs. 66% vs. 3%); and all-cause mortality (15% vs. 65% vs. 20%). Studies (n = 84) inconsistently adhered to methodologic standards. Although 90% provided eligibility criteria; 61% cited participation rates; and 73% described the methods used to measure alcohol exposure; only 44% adjusted for potentially important confounding factors; and 26% distinguished former drinkers from nondrinkers. Of the cohort studies (n = 47), 30% assessed for change in participants' exposure status over time, and 17% determined whether losses to follow-up varied by exposure status. The magnitude of risk posed by alcohol use for falls or fall injuries, functional disability, cognitive impairment, and all-cause mortality among older adults remains uncertain. Prospective studies are needed to better define the health-related effects of alcohol use in older populations.

Oestrogen has neuroprotective effects and may reduce the risk of Alzheimer's disease

Evidence from both animals and humans supports a neuroprotective role of oestrogen. Epidemiological studies showing that oestrogen improves cognitive performance in postmenopausal women, clinical trials showing effects of oestrogen on cognition and data suggesting that oestrogen reduces the risk of Alzheimer's disease (AD) led to the proposal that oestrogen may be effective for improving symptoms or slowing decline in women with AD. Studies evaluating oestrogen as a treatment for AD have been performed with mixed findings. While a few studies have found modest improvements, the results have largely been disappointing. However, many of the studies suffer from substantial methodological problems that leave the findings in question. The role of oestrogen for the prevention or treatment of AD is not yet clear, but large, well-controlled, ongoing trials should provide definitive answers to many questions in the near future.

Prevalence of dementia in users of hormone replacement therapy as defined by prescription data

BACKGROUND

Studies of hormone replacement therapy (HRT) and dementia and cognitive impairment show mixed results. This study assessed the prevalence of dementia and cognitive impairment in users and nonusers of HRT defined using computer-stored prescription information.

METHODS

The study involved 3924 women 75 years of age and older who were members of the Southern California Kaiser Permanente Medical Care Program in 1998. HRT use was determined based on prescription data for 1992-1998. Cognitive function and dementia were assessed using the Telephone Interview of Cognitive Status supplemented by the Telephone Dementia Questionnaire and medical record review.

RESULTS

Odds ratios (ORs) for cognitive impairment/dementia showed expected associations with age, education, ethnicity, and a history of stroke or Parkinson's disease. After adjustment, the OR for cognitive impairment or dementia in HRT users compared with HRT nonusers was 0.91 (95% confidence interval 0.75-1.10). The adjusted ORs for all dementia and dementia without cause in HRT users compared with nonusers were 0.77 (95% confidence interval 0.59- 1.00) and 0.78 (0.58-1.05), respectively. Twenty percent of women with cognitive impairment or dementia who had been classified as HRT users by prescription (one prescription each year from 1992-1998) denied hormone use compared with 8.8% of women without impairment. Medical record review validated prescription information for the impaired women.

CONCLUSIONS

The study identified an important methodologic problem in studies of HRT and cognitive impairment and dementia that depend on recalled information about drug exposure. A protective effect of HRT for cognitive impairment and dementia was neither established nor ruled out based on the prescription data.

Familial and environmental risk factors in Parkinson's disease: a case-control study in north-east Italy

BACKGROUND AND OBJECTIVE

The aetiology of Parkinson's disease remains unknown, although both genetic susceptibility and environmental factors are considered putative contributors to its origin. We performed a case-control study to investigate the association of familial and environmental risk factors with Parkinson's disease (PD).

METHODS

We studied 136 patients with neurologist confirmed PD and 272 age- and sex-matched controls, affected by neurological diseases not related to PD. The risk of developing idiopathic PD associated with the following familial and environmental factors: positive family history of PD, positive family history of essential tremor (ET), age of mother at subject's birth, rural birth, rural living, well water use, farming as an occupation, exposure to pesticides, head tremor, exposure to general anaesthesia and to ionizing radiations, food restriction, concentration camp imprisonment and smoking has been assessed by using univariate and multivariate statistical techniques.

RESULTS

In the conditional multiple logistic regression analysis, positive family history of PD (OR 41.7, 95% CI 12.2-142.5, P < 0.0001), positive family history of ET (OR 10.8, 95% CI 2.6-43.7, P < 0.0001), age of mother at subject's birth (OR 2.6, 95% CI 1.4-3.7, P=0.0013), exposure to general anaesthesia (OR 2.2, 95% CI 1.3-3.8, P=0.0024), farming as an occupation (OR 7.7, 95% CI 1.4-44.1, P=0.0212) and well water use (OR 2.0, 95% CI 1.1-3.6, P=0.0308) exhibited a significant positive association with PD, whereas smoking showed a trend toward an inverse relationship with PD (OR 0.7, 95% CI 0.4-1.1, P < 0.06).

CONCLUSIONS

We conclude that both familial and environmental factors may contribute to PD aetiology.

Estrogen replacement therapy for cognitive benefits: viable treatment or forgettable "senior moment"?

The perceived benefits of estrogen on cognitive function are one of the few remaining potential roles for estrogen replacement therapy. The justification for such a role has a strong biologic basis and is easily shown in animal models. Purported benefits for estrogen on cognitive function include neuroprotective, neurostimulating, and neurotrophic effects. The objective of this study was to review the literature and to evaluate the role of estrogen replacement therapy in improving cognition in Alzheimer disease, vascular dementia, premenopausal women, and postmenopausal women without dementia. Additionally, the authors separately looked at the neuroprotective effects of estrogen replacement therapy on the subsequent risk of dementia. The available data fail to show a therapeutic benefit of estrogen replacement therapy in Alzheimer disease. Surprisingly, limited data allow consideration of a possible role of estrogen in the management of vascular dementia. Additionally, younger females with low estrogen levels secondary to primary ovarian failure and Turner syndrome benefit from estrogen replacement therapy. Despite the limited role of estrogen replacement therapy in cognitive enhancement, neuroprotective properties are likely because several prospective studies indicate a reduced risk of Alzheimer disease. A critical window of opportunity seems to exist for this protective effect in Alzheimer disease because once established, the course of the disease is not affected by concomitant estrogen replacement therapy. The authors conclude that the use of estrogen replacement therapy is not substantiated for the treatment of patients with Alzheimer disease. Alternatively, because of the evidence for a possible neuroprotective effect, women at high risk for the development of Alzheimer disease may be appropriate candidates for estrogen replacement therapy. Such a decision should be made on a case-by-case basis, after careful consideration of the risks and benefits.

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.

Long-term estrogen replacement is associated with improved nonverbal memory and attentional measures in postmenopausal women

OBJECTIVE

To determine the cognitive domains improved or preserved by long-term hormone replacement therapy (HRT).

DESIGN

A comprehensive neuropsychological test battery was administered to healthy postmenopausal women who had been treated or not treated with long-term HRT without interruption since menopause.

SETTING

Women were recruited by advertisement from a university town and surrounding areas.

PATIENT(S)

Women 60 years or older were studied who were treated (n = 16) or not treated (n = 13) with HRT.

INTERVENTION(S)

Neuropsychological testing included tests of memory, verbal fluency, executive functions, attention and concentration, and psychomotor function. Tests of intellectual function, depressive symptoms, and emotional functioning assessed general functions and comparability of the groups.

MAIN OUTCOME MEASURE(S)

Neuropsychological testing scores were compared between groups.

RESULT(S)

No statistically significant differences between the groups were found for general demographic, intellectual, and psychological measures. Scores from both the Weschler Memory Scale Visual Reproduction (delayed recall) and the Digit Vigilance Test (attention) showed statistically significant better performance and fewer errors in the group of women on HRT.

CONCLUSION(S)

Long-term postmenopausal HRT is associated with higher scores in tests of nonverbal memory and attention.

Estrogens, selective estrogen receptor modulators, and dementia: what is the evidence?

At least 10% of people aged 65 or older have some form of cognitive impairment, increasing to around 50% by age 85. Several studies have suggested that estrogen may improve cognitive function or prevent the development of dementia, but other studies have not shown a benefit, and results from large randomized trials are lacking. Fortunately, further trials are currently being conducted. With the recognition that selective estrogen receptor modulators (SERMs) have differential tissue-dependent effects on estrogen receptor function, there is recent interest in the effects of raloxifene, tamoxifen, and other SERMs on cognition. In this paper, the current state of knowledge of the role of estrogen for preventing dementia in postmenopausal women will be reviewed. In addition, the status of ongoing and recently completed trials of estrogen and SERMs on cognitive function or on Alzheimer's disease severity will be summarized.

Nonsteroidal antiinflammatory drugs and the risk of Alzheimer's disease

BACKGROUND

Previous studies have suggested that the use of nonsteroidal antiinflammatory drugs (NSAIDs) may help to prevent Alzheimer's disease. The results, however, are inconsistent.

METHODS

We studied the association between the use of NSAIDs and Alzheimer's disease and vascular dementia in a prospective, population-based cohort study of 6989 subjects 55 years of age or older who were free of dementia at base line, in 1991. To detect new cases of dementia, follow-up screening was performed in 1993 and 1994 and again in 1997 through 1999. The risk of Alzheimer's disease was estimated in relation to the use of NSAIDs as documented in pharmacy records. We defined four mutually exclusive categories of use: nonuse, short-term use (1 month or less of cumulative use), intermediate-term use (more than 1 but less than 24 months of cumulative use), and long-term use (24 months or more of cumulative use). Adjustments were made by Cox regression analysis for age, sex, education, smoking status, and the use or nonuse of salicylates, histamine Hz-receptor antagonists, antihypertensive agents, and hypoglycemic agents.

RESULTS

During an average follow-up period of 6.8 years, dementia developed in 394 subjects, of whom 293 had Alzheimer's disease, 56 vascular dementia, and 45 other types of dementia. The relative risk of Alzheimer's disease was 0.95 (95 percent confidence interval, 0.70 to 1.29) in subjects with short-term use of NSAIDs, 0.83 (95 percent confidence interval, 0.62 to 1.11) in those with intermediate-term use, and 0.20 (95 percent confidence interval, 0.05 to 0.83) in those with long-term use. The risk did not vary according to age. The use of NSAIDs was not associated with a reduction in the risk of vascular dementia.

CONCLUSIONS

The long-term use of NSAIDs may protect against Alzheimer's disease but not against vascular dementia.

Neuroimaging of aging and estrogen effects on central nervous system physiology

OBJECTIVE

To review the literature on neuroimaging studies focusing on gender differences in the aging process and on the effects of postmenopausal estrogen use on the brain.

DESIGN

Pertinent studies were identified through a computer MEDLINE search. References of selected articles were hand-searched for additional citations.

CONCLUSION(S)

The current literature suggests that estrogen replacement may decrease brain white matter lesions, increase cerebral blood flow, alter regional brain activation patterns during cognitive processing, and have modulatory effects on various neurotransmitter systems. Overall, this points to a functional plasticity in higher order brain processing that can be altered by gonadal steroids.

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.

Alzheimer's disease: insights from epidemiology

While a complete understanding of the pathogenesis of Alzheimer's disease (AD) remains elusive, many conclusions can be drawn from the numerous epidemiological studies undertaken to date. Prevalence and incidence estimates show consistency, following a roughly exponential pattern with a doubling of both parameters roughly every five years after age 65. Roughly 7% of the population aged 65 and over has AD. The clinical course of the disease is reasonably well established and mortality rates rise with increasing levels of cognitive deficit. Four risk factors for AD are firmly established: increasing age, the presence of the apolipoproteinE-epsilon4 allele, familial aggregation of cases, and Down's syndrome. Numerous other associations have been shown in some studies, but not in others. For example, women generally appear at higher risk than men, as do people with lower levels of education; depression is probably prodromal; head injury is an established risk factor, and may interact with the apoE gene; several occupational exposures appear hazardous, and exposure to aluminum in the water supply confers excess risk. Hypertension and other vascular symptoms appear to predispose to AD, which is now seen as nosologically closer to vascular dementia than was previously believed. Several apparently protective factors have been identified, although preventive trials based on these have so far shown minimal effectiveness. The use of non-steroidal anti-inflammatory drugs to treat arthritis is associated with a reduced risk of AD, as is estrogen use by post-menopausal women. Physical activity appears beneficial, as does a diet with high levels of vitamins B6, B12 and folate. while red wine in moderate quantities appears protective. This review concludes with a discussion of the strengths and limitations of current epidemiological methods for studying Alzheimer's disease.

Aluminium as a risk factor in Alzheimer's disease, with emphasis on drinking water

Aluminium (Al) is clearly a powerful neurotoxicant. Considerable evidence exists that Al may play a role in the aetiology or pathogenesis of Alzheimer's disease (AD), but whether the link is causal is still open to debate. This paper reviews the epidemiological evidence linking Al and AD. Nine out of 13 published epidemiological studies of Al in drinking water and AD have shown statistically significant positive relations. Given the difficulty in producing high-quality data for the occurrence of AD and also for Al exposure, with the resulting unavoidable misclassification errors biasing any true association towards the null value, these studies are remarkably consistent. A major problem in their interpretation is that drinking water, even at high Al concentrations, only contributes a fraction of the total dietary intake of Al. In particular, regular consumers of antacids ingest gram amounts of Al daily, thousands of times the amounts taken in through drinking water, and epidemiological studies of antacid exposure and AD have been largely negative. However, Al is very poorly absorbed in the gastrointestinal tract, and the possibility that some Al fractions present in drinking water may be particularly bioavailable cannot be dismissed at present. The combined evidence linking Al and AD warrants substantial research efforts. Such efforts should focus on clarification of the cellular and molecular mechanisms in Al toxicity and of the basic metabolism and kinetics of Al in the human body, and on further epidemiological studies including diverse routes of Al exposure and also variables that are known or suspected to influence the individuals' susceptibility to AD, such as apolipoprotein E allele status and family history of AD.

The nature of the effect of female gonadal hormone replacement therapy on cognitive function in post-menopausal women: a meta-analysis

We reviewed epidemiological and experimental studies of female gonadal hormone replacement therapy (HRT) on cognitive function in post-menopausal women and carried out meta-analyses. In healthy ageing women, HRT has small and inconsistent effects that include enhancement of verbal memory, abstract reasoning and information processing. Epidemiological studies show larger effects than experimental studies, which is not related to sample size. Important confounds may be that women who start using HRT are healthier than women who do not. Also, controlling for socio-economic status diminishes the effect of HRT. The effects of HRT may depend on the age and type of menopause and the therapeutic intervention used, with the most widely used drug, Premarin, having least effect. However, the effects are independent of mood and climacteric symptom alleviation. There is a paucity of experimental studies that include healthy elderly women. The evidence for an estrogen deficiency in women with dementia and cognitive dysfunction is inconsistent. Nevertheless, epidemiological studies suggest that HRT protects against the development of clinically diagnosed Alzheimer's disease. However, poor recall of HRT use by patients and altered physician behaviour may have confounded the effects. Surprisingly, both healthy and demented women with low education seem to benefit most from HRT. Three recent controlled experimental studies using Premarin showed no effects of HRT in preventing further cognitive decline in women who already have Alzheimer's disease. Duration of treatment seems to play an important role, with beneficial effects declining-and even reversing-with longer treatment in women with Alzheimer's disease.Future research should further investigate the cognitive effect of different HRT preparations, serum estrogen levels, and the interactions of HRT with age, menopausal status and existing protective (e.g. education) and risk factors (e.g. smoking and apolipoprotein E genotype) for cognitive decline and Alzheimer's disease.

The association between smoking and Alzheimer's disease: effects of study design and bias

In epidemiologic studies, unrecognized bias can contribute to observed results, causing them to be inaccurate. Analytic study designs, such as the case-control and cohort designs, each carry potential for specific forms of bias. The cohort design is not susceptible to many forms of bias that are experienced by case-control studies. A consistent "protective" effect of smoking on Alzheimer's disease was documented by many case-control studies. However, the potential effect of biases cannot be separated from the results. Cohort studies now show that smoking may either be unrelated to Alzheimer's disease onset or possibly generate a modest increased risk. In this review the results and comparisons of various studies and potential biases are discussed.

Estrogen use among nursing home residents with a diagnosis of Parkinson's disease

BACKGROUND

The role of estrogen in motor, cognitive, and behavioral functions in Parkinson's disease (PD) remains unclear.

OBJECTIVES/METHODS

To determine differences in functional, cognitive, and behavioral patterns between estrogen users and non-users, we performed an observational study on 10,145 elderly women with PD using the Systematic Assessment in Geriatric drug use via Epidemiology (SAGE) database. The SAGE database consists of the Minimum Data Set (MDS), data collected on a cross-section of over 400,000 nursing home (NH) residents in five US states. Using a cross-sectional study design, we evaluated the demographics, physical and cognitive function, and mortality rates of women with PD who received estrogen (n = 195) versus those who did not receive estrogen (n = 9950).

RESULTS

Independent of age, estrogen users were less cognitively impaired and more independent in their activities of daily living. Surprisingly, more estrogen users were depressed and more likely to be on an antidepressant than non-users. One-year death rates were comparable between estrogen users and non-users.

CONCLUSION

This study supports the growing number of recent data suggesting estrogen's potential beneficial effects on PD motor and cognitive functions.

Outcome following traumatic brain injury in the elderly: a critical review

BACKGROUND

The elderly are at risk for traumatic brain injury (TBI), but their outcome following these injuries remains unclear.

OBJECTIVE

This paper critically reviews research done to date on cognitive and functional outcome following TBI in the elderly.

METHODS

MEDLINE and PSYCHLIT databases going back to 1965 were searched.

RESULTS

Studies suggest that TBI results in adverse cognitive and functional outcomes in the elderly. There is uncertainty as to whether TBI is a significant risk factor for Alzheimer's disease (AD). Methodological problems in these studies include selection bias, small samples, retrospective analyses, and, particularly, the failure to address the role of pre-morbid functioning. These problems limit the strength of the outcome studies, and may account for the equivocal findings on AD risk.

CONCLUSIONS

It is premature to conclude from the published research to date that the elderly have a uniformly poor outcome following TBI. Directions for further research are suggested.

Smoking and Parkinson's and Alzheimer's disease: review of the epidemiological studies

The relationship between smoking and neurological diseases has always been controversial. Even the expected association between smoking and increased risk for cerebrovascular disease has been debated for years. It was at the end of the 1980s that smoking became definitively accepted as a risk factor for ischemic stroke. More recently, two other neurological diseases have been studied in relation to smoking: Parkinson's disease (PD) and Alzheimer's disease (AD). Many epidemiological studies have found a highly significant negative association between cigarette smoking and these two neurodegenerative disorders. The risk of AD or PD in nonsmokers has generally been about twice that of smokers. That is, patients with AD or PD are approximately 50% less likely to have smoked cigarettes during their lifetime than are age- and gender-matched controls. Alternatively, cigarette smokers are 50% less likely to have PD or AD than are age- and gender-matched nonsmokers. This statistically significant negative association has been interpreted as suggesting that cigarette smoking exerts an undefined, biologic, neuroprotective influence against the development of PD and AD. A review of all studies that either support or refute this hypothesis is presented separately for PD and AD.

Traumatic brain injury as a risk factor for Alzheimer's disease: a review

Accumulating epidemiological evidence implicates traumatic brain injury as a pathogenic agent in the development of Alzheimer's disease (AD). Considering the increase in the prevalence of both traumatic brain injury and AD in recent times, the possibility that brain trauma may provoke the early development of AD has important implications for health service planning, preventative efforts, and medico-legal compensation settlements. This paper evaluates the plausibility of the proposed link between traumatic brain injury and AD, largely by way of exploring a theoretical perspective advanced by Satz (1993) and considering recent contributions from the epidemiological, neuropathological, and biochemical literature that are pertinent to this issue. The literature reviewed provides sufficient support and empirical vindication to give credence to the proposed association between these two neuropsychological entities at the statistical, theoretical, and biological level.

Smoking, drinking, and incident cognitive impairment: a cohort community based study included in the Gospel Oak project

OBJECTIVES

Recent longitudinal studies have reported that smoking increases risk for cognitive impairment and that moderate alcohol intake could be preventive. The association between both cigarette smoking and alcohol drinking and incident cognitive impairment was studied in a representative population.

METHODS

This is a 1 year prospective population based cohort study of all residents aged 65 or over in the electoral ward of Gospel Oak in London, UK (n=889). Cognitive impairment was assessed at baseline and 1 year later using the organic brain syndrome (OBS) cognitive impairment scale from the short CARE structured assessment. Subjects who were cognitively impaired at baseline were excluded from this analysis.

RESULTS

The prevalence of OBS cognitive impairment was 10.4% at index assessment and the 1 year cumulative incidence of cognitive impairment was 5.7%. Cognitive impairment was not associated with use of alcohol, although there was a non-significant association in the direction of a protective effect against onset of cognitive impairment for moderate drinkers compared with non-drinkers and heavy drinkers. Current smoking status predicted cognitive impairment (risk ratio (RR) 3.7; (95% confidence interval (95% CI)=1.1-12.3) independently from sex, age, alcohol, occupational class, education, handicap, depression, and baseline cognitive function.

CONCLUSIONS

Smoking seems to be a prospective risk factor for incident cognitive impairment; thus encouragement of older people to stop smoking could be considered as part of a strategy to reduce the incidence of cognitive impairment.

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.

Alzheimer's disease and down syndrome: from meiosis to dementia

Several molecular and clinical similarities have been detected in Alzheimer's disease (AD) and Down syndrome (DS). The most remarkable feature is abnormal accumulation of beta-amyloid in the brains of both individuals affected with AD and aging DS patients followed by dementia. In addition, AD patients exhibit dermatoglyphic patterns similar to those in DS, and late maternal age is a risk factor in both diseases. AD and DS could be related genetically because AD families exhibit a higher rate of DS cases and vice versa. Although numerous discoveries have been made in the elucidation of the etiopathogenic factors in AD and DS, little progress has been achieved in understanding the origin of the common features of the two diseases. This article reviews clinical and molecular similarities in DS and AD and also chromosome 21 studies in both diseases. A new hypothesis explaining the association between AD and DS is suggested, and this hypothesis is based on the poorly understood molecular phenomenon of aberrant meiotic recombination. Aberration in meiotic recombination has been consistently detected in chromosomal diseases including trisomy 21 and sex chromosomes. There are no studies dedicated to meiotic recombination in genetic diseases; however, evidence for disturbed recombination has been documented in several neurological diseases such as Huntington's disease, myotonic dystrophy, and fragile X syndrome. Interestingly, the rate of trisomic XXY children born to mothers transmitting fragile X mutation is higher than expected. This finding suggests that AD could be associated with DS in a similar way to which fragile X syndrome is related to trisomy of sex chromosomes. Based on analogy with fragile X syndrome, it can be predicted that AD should demonstrate aberrant meiotic recombination in chromosome 21, most likely in the region D21S1/S11-D21S16 which is linked to early onset familial AD. Based on the same rationale, different patterns of meiotic recombination in the nondisjunct chromosome 21 within DS patients grouped according to the concomitant disease are predicted.