Education and occupation as risk factors for dementias of the Alzheimer and ischemic vascular types

Cognitive reserve moderates the association between cerebral blood flow and language performance in older adults with mild cognitive impairment

Higher cognitive reserve (CR) may offer protection from cognitive changes associated with reduced cerebral blood flow (CBF). We investigated CR as a moderator of the effect of CBF on cognition in older adults with mild cognitive impairment (MCI; N = 46) and those who are cognitively unimpaired (CU; N = 101). Participants underwent arterial spin labeling MRI, which was used to quantify CBF in 4 a priori regions. Estimated verbal intelligence quotient (VIQ) served as a proxy for CR. Multiple linear regressions examined whether VIQ moderated associations between CBF and cognition and whether this differed by cognitive status. Outcomes included memory and language performance. There were 3-way interactions (CBF*VIQ*cognitive status) on category fluency when examining hippocampal, superior frontal, and inferior frontal CBF. Follow-up analyses revealed that, within the MCI but not CU group, there were CBF*VIQ interactions on fluency in all a priori regions examined, where there were stronger, positive associations between CBF and fluency at higher VIQ. Conclusion: In MCI, higher CR plays a role in strengthening CBF-fluency associations.

Normalization of Cerebral Blood Flow, Neurochemicals, and White Matter Integrity after Kidney Transplantation

BACKGROUND

CKD is associated with abnormalities in cerebral blood flow, cerebral neurochemical concentrations, and white matter integrity. Each of these is associated with adverse clinical consequences in the non-CKD population, which may explain the high prevalence of dementia and stroke in ESKD. Because cognition improves after kidney transplantation, comparing these brain abnormalities before and after kidney transplantation may identify potential reversibility in ESKD-associated brain abnormalities.

METHODS

In this study of patients with ESKD and age-matched healthy controls, we used arterial spin labeling to assess the effects of kidney transplantation on cerebral blood flow and magnetic resonance spectroscopic imaging to measure cerebral neurochemical concentrations (N-acetylaspartate, choline, glutamate, glutamine, myo-inositol, and total creatine). We also assessed white matter integrity measured by fractional anisotropy (FA) and mean diffusivity (MD) with diffusion tensor imaging. We used a linear mixed model analysis to compare longitudinal, repeated brain magnetic resonance imaging measurements before, 3 months after, and 12 months after transplantation and compared these findings with those of healthy controls.

RESULTS

Study participants included 29 patients with ESKD and 19 controls; 22 patients completed post-transplant magnetic resonance imaging. Cerebral blood flow, which was higher in patients pretransplant compared with controls (P=0.003), decreased post-transplant (P<0.001) to values in controls. Concentrations of neurochemicals choline and myo-inositol that were higher pretransplant compared with controls (P=0.001 and P<0.001, respectively) also normalized post-transplant (P<0.001 and P<0.001, respectively). FA increased (P=0.001) and MD decreased (P<0.001) post-transplant.

CONCLUSIONS

Certain brain abnormalities in CKD are reversible and normalize with kidney transplantation. Further studies are needed to understand the mechanisms underlying these brain abnormalities and to explore interventions to mitigate them even in patients who cannot be transplanted.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

Cognitive Impairment and Imaging Correlates in End Stage Renal Disease, NCT01883349.

The influence of childhood intelligence, social class, education and social mobility on memory and memory decline in late life

In an observational longitudinal study of a sub-sample of the Aberdeen 1936 birth cohort, from age 62 to 77 years, we investigated childhood intelligence, social class, education, life-course social mobility, memory test performance and memory decline in late life. We examined 388 local residents who had attended school in Aberdeen in 1947 and measured Auditory-Verbal Learning Test (AVLT) at recruitment age about 64 years and up to five times until age about 77 years. Better performance at age about 64 on AVLT was predicted by early socioeconomic status (SES), social mobility and childhood intelligence. The trajectory of AVLT decline was steeper in those who had received less education. This relationship was independent of childhood ability, sex, SES in childhood and social mobility. The protection of memory by education suggests that education supports resilience to age-related cognitive impairment. Upward social mobility does not enhance this effect, suggesting that resilience to age-related decline may be established in early life.

Patient characteristics associated with screening positive for Alzheimer's disease and related dementia

INTRODUCTION

Screening all older adults for Alzheimer's disease and related dementias (ADRD) in primary care may not be acceptable or feasible. The goal of this study was to identify factors that could optimize screening in primary care and enhance its feasibility.

METHODS

This is a cross-sectional study in rural, suburban, and urban primary care practices in Indiana. A total of 1,723 patients ≥65 years of age were screened for ADRD using the Memory Impairment Screen. Logistic regression was used to identify patient-specific factors associated with screening positive for ADRD.

RESULTS

The positive screening rate was 4.9%. Rates varied significantly across the three study sites. The rural site had the lowest rate (2.8%), which was significantly lower than the rates at the suburban (5.6%) and urban (6.6%) sites (P<0.01). Patient age, sex, and education were significantly (P<0.05) associated with screening positive for ADRD.

CONCLUSION

Targeted screening of patients at risk for ADRD may represent a more optimal and feasible screening alternative to population screening.

Education as a Protective Factor Moderating the Effect of Depression on Memory Impairment in Elderly Women

OBJECTIVE

The cognitive reserve theory explicates individual differences observed in the clinical manifestation of dementia despite similar brain pathology. Education, a popular proxy of the cognitive reserve, has been shown to have protective effects delaying the onset of clinical symptoms including memory. This study was conducted to test whether education can moderate the negative effect of depressive mood on memory performance in elderly women residing in the community.

METHODS

29 elderly "unschooled" female (less than 6 years of formal education) and 49 "schooled" female (6 or more years) people were compared with regard to association between depressive mood and verbal memory functioning, which were measured by the Geriatric Depression Scale and the Elderly Verbal Learning Test, respectively.

RESULTS

The results showed that completing or receiving more than primary school education significantly reduced the negative association between depressive mood and memory performance. Participants who did not complete primary schooling showed a decline in memory test scores depending on the level of depressive mood; whereas participants who have completed or received more than primary education displayed relatively stable memory function despite varying level of depressive mood.

CONCLUSION

Our findings imply that education in early life may have protective effects against memory impairment related to elderly depression.

Contribution of Socioeconomic Status at 3 Life-Course Periods to Late-Life Memory Function and Decline: Early and Late Predictors of Dementia Risk

Both early life and adult socioeconomic status (SES) predict late-life level of memory; however, evidence is mixed on the relationship between SES and rate of memory decline. Further, the relative importance of different life-course periods for rate of late-life memory decline has not been evaluated. We examined associations between life-course SES and late-life memory function and decline. Health and Retirement Study participants (n = 10,781) were interviewed biennially from 1998-2012 (United States). SES measurements for childhood (composite score including parents' educational attainment), early adulthood (high-school or college completion), and older adulthood (income, mean age 66 years) were all dichotomized. Word-list memory was modeled via inverse-probability weighted longitudinal models accounting for differential attrition, survival, and time-varying confounding, with nonrespondents retained via proxy assessments. Compared to low SES at all 3 points (referent), stable, high SES predicted the best memory function and slowest decline. High-school completion had the largest estimated effect on memory (β = 0.19; 95% confidence interval: 0.15, 0.22), but high late-life income had the largest estimated benefit for slowing declines (for 10-year memory change, β = 0.35; 95% confidence interval: 0.24, 0.46). Both early and late-life interventions are potentially relevant for reducing dementia risk by improving memory function or slowing decline.

Decreased expression of the APOA1-APOC3-APOA4 gene cluster is associated with risk of Alzheimer's disease

Background

Apolipoprotein is genetically associated with the risk of Alzheimer’s disease (AD). The APOA1, APOC3, and APOA4 genes are closely linked and located on human chromosome 11. Therefore, this gene cluster may be related to the risk of AD.

Patients and methods

A total of 147 AD patients and 160 healthy controls were randomly recruited from June 2013 to August 2014. APOA1, APOC3, and APOA4 levels were measured using real-time quantitative reverse-transcriptase polymerase chain reaction and enzyme-linked immunosorbent assay.

Results

APOA1, APOC3 and APOA4 levels were significantly lower in AD patients than controls (P<0.01). APOA1, APOC3, and APOA4 levels were negatively related with the severities of AD determined by Clinical Dementia Rating scores (P<0.01). APOA1, APOC3, and APOA4 levels showed a negative relation with Montgomery–Åsberg Depression Rating Scale scores and a positive relation with RAND 36-item health-survey scores (P<0.01). There was a decreased trend for levels of APOA1, APOC3, and APOA4 in AD patients.

Conclusion

Low levels of APOA1, APOC3, and APOA4 are associated with risk of AD. APOA1, APOC3, and APOA4 should be developed as combined drugs for the therapy of AD.

Slow Progression of Cognitive Dysfunction of Alzheimer's Disease in Sexagenarian Women with Schizophrenia

Although both schizophrenia (SCZ) and Alzheimer's disease (AD) are among the most common psychiatric diseases, the interaction of these two is not well-understood. We investigated three women with SCZ who developed AD in their 60s. The patients presented with cognitive dysfunction such as loss of recent memory, which was confirmed by both clinical observations and neuropsychological tests. Their magnetic resonance and functional imaging findings were consistent with AD. Their brain atrophy advanced significantly during a 6-year observation period. However, their global cognitive function did not deteriorate significantly during this period. Although the cognitive reserve model might account for this discrepancy, our results suggest some interactions between the neuropathology of SCZ and AD and warrant further research.

Vascular risk as a predictor of cognitive decline in a cohort of elderly patients with mild to moderate dementia

Background/Aims

The purpose of our study was to evaluate vascular risk factors and other clinical variables as predictors of cognitive and functional decline in elderly patients with mild to moderate dementia.

Methods

The clinical characteristics of 82 elderly patients (mean age 79.0 ± 5.9 years; 67.1% females) with mild to moderate dementia were obtained at baseline, including years of education, Framingham Coronary Heart Disease Risk score, Hachinski Ischemic Score (HIS), Clinical Dementia Rating (CDR), Mini-Mental State Examination (MMSE) score, Functional Activities Questionnaire (FAQ) score, Burden Interview Scale score, and Neuropsychiatric Inventory (NPI) score. Changes in MMSE and FAQ scores over time were assessed annually. The association between baseline clinical variables and cognitive and functional decline was investigated during 3 years of follow-up through the use of generalized linear mixed effects models.

Results

A trend was found towards steeper cognitive decline in patients with less vascular burden according to the HIS (β = 0.056, p = 0.09), better cognitive performance according to the CDR score (β = 0.313, p = 0.06) and worse caregiver burden according to the Burden Interview Scale score (β = −0.012, p = 0.07) at baseline.

Conclusion

Further studies with larger samples are necessary to confirm and expand our findings.

Cognitive reserve moderates relation between global cognition and functional status in older adults

The ability to perform instrumental activities of daily living (IADLs) is necessary for independent living. Research suggests that community-dwelling older adults are at risk for experiencing subtle decrements in the performance of IADLs. Neuropsychological tests have been used to account for differences in IADL status. Studies of the relationship between cognitive ability and functional status have produced variable results, however, and cognitive ability appears to be only a moderate predictor. Several studies of normal aging have revealed cognitive and functional benefits of higher cognitive reserve (CR) in healthy, nondemented older adults. The purposes of the present study were to: (a) examine the relationship between global cognitive ability and IADL performance among 53 community-dwelling older adults, and (b) determine whether formal education, as a proxy of CR, significantly moderates this relationship. Consistent with previous findings, global cognitive ability accounted for a considerable portion of variance in IADL performance [ΔR(2) = .54; ΔF(2, 53) = 67.96; p < .001]. Additionally, CR modestly but significantly attenuated this relationship [ΔR(2) = .044; ΔF(4, 53) = 5.98; p = .018; total R(2) = .65]. This finding suggests that community-dwelling older adults with lower levels of formal education may be at greater risk for functional decrements associated with age-related cognitive decline.

High cognitive reserve is associated with a reduced age-related deficit in spatial conflict resolution

Several studies support the existence of a specific age-related difficulty in suppressing potentially distracting information. The aim of the present study is to investigate whether spatial conflict resolution is selectively affected by aging. The way aging affects individuals could be modulated by many factors determined by the socieconomic status: we investigated whether factors such as cognitive reserve (CR) and years of education may play a compensatory role against age-related deficits in the spatial domain. A spatial Stroop task with no feature repetitions was administered to a sample of 17 non-demented older adults (69-79 years-old) and 18 younger controls (18-34 years-old) matched for gender and years of education. The two age groups were also administered with measures of intelligence and CR. The overall spatial Stroop effect did not differ according to age, neither for speed nor for accuracy. The two age groups equally showed sequential effects for congruent trials: reduced response times (RTs) if another congruent trial preceded them, and accuracy at ceiling. For incongruent trials, older adults, but not younger controls, were influenced by congruency of trial(n-1), since RTs increased with preceding congruent trials. Interestingly, such an age-related modulation negatively correlated with CR. These findings suggest that spatial conflict resolution in aging is predominantly affected by general slowing, rather than by a more specific deficit. However, a high level of CR seems to play a compensatory role for both factors.

Relationship between education and dementia: an updated systematic review

OBJECTIVE

The purpose of this study was to review the relationship between education and dementia.

METHODS

A systematic literature review was conducted of all published studies examining the relationship between education and dementia listed in the PubMed and PsycINFO databases from January 1985 to July 2010. The inclusion criteria were a measure of education and a dementia diagnosis by a standardized diagnostic procedure. Alzheimer disease and Total Dementia were the outcomes.

RESULTS

A total of 88 study populations from 71 studies met inclusion criteria. Overall, 51 studies (58%) reported significant effects of lower education on risk for dementia, whereas 37 studies (42%) reported no significant relationship. A relationship between education and risk for dementia was more consistent in developed regions compared with developing regions. Age, sex, race/ethnicity, and geographical region moderated the relationship.

CONCLUSIONS

Lower education was associated with a greater risk for dementia in many but not all studies. The level of education associated with risk for dementia varied by study population and more years of education did not uniformly attenuate the risk for dementia. It seemed that a more consistent relationship with dementia occurred when years of education reflected cognitive capacity, suggesting that the effect of education on risk for dementia may be best evaluated within the context of a lifespan developmental model.

Is cognitive aging predicted by one's own or one's parents' educational level? results from the three-city study

The authors examined the associations of participants' and their parents' educational levels with cognitive decline while addressing methodological limitations that might explain inconsistent results in prior work. Residents of Dijon, France (n = 4,480) 65 years of age or older who were enrolled between 1999 and 2001 were assessed using the Isaacs' verbal fluency test, Benton Visual Retention Test, Trail Making Test B, and Mini-Mental State Examination up to 5 times over 9 years. The authors used random-intercepts mixed models with inverse probability weighting to account for differential survival (conditional on past performance) and quantile regressions to assess bias from measurement floors or ceilings. Higher parental educational levels predicted better average baseline performances for all tests but a faster average decline in score on the Isaacs' test. Higher participant educational attainment predicted better baseline performances on all tests and slower average declines in Benton Visual Retention Test, Trail Making Test B, and Mini-Mental State Examination scores. Slope differences were generally small, and most were not robust to alternative model specifications. Quantile regressions suggested that ceiling effects might have modestly biased effect estimates, although the direction of this bias might depend on the test instrument. These findings suggest that the possible impacts of educational experiences on cognitive change are small, domain-specific, and potentially incorrectly estimated in conventional analyses because of measurement ceilings.

Education increases reserve against Alzheimer's disease--evidence from structural MRI analysis

Introduction

The aim of this study was to determine whether years of schooling influences regional cortical thicknesses and volumes in Alzheimer’s disease (AD), mild cognitive impairment (MCI), and healthy age-matched controls.

Methods

Using an automated image analysis pipeline, 33 regional cortical thickness and 15 regional volumes measures from MRI images were determined in 121 subjects with MCI, 121 patients with AD, and 113 controls from AddNeuroMed study. Correlations with years of schooling were determined and more highly and less highly educated subjects compared, controlling for intracranial volume, age, gender, country of origin, cognitive status, and multiple testing.

Results

After controlling for confounding factors and multiple testing, in the control group, subjects with more education had larger regional cortical thickness in transverse temporal cortex, insula, and isthmus of cingulate cortex than subjects with less education. However, in the AD group, the subjects with more education had smaller regional cortical thickness in temporal gyrus, inferior and superior parietal gyri, and lateral occipital cortex than the subjects with less education. No significant difference was found in the MCI group.

Conclusion

Education may increase regional cortical thickness in healthy controls, leading to increased brain reserve, as well as helping AD patients to cope better with the effects of brain atrophy by increasing cognitive reserve.

Education does not slow cognitive decline with aging: 12-year evidence from the victoria longitudinal study

Although the relationship between education and cognitive status is well-known, evidence regarding whether education moderates the trajectory of cognitive change in late life is conflicting. Early studies suggested that higher levels of education attenuate cognitive decline. More recent studies using improved longitudinal methods have not found that education moderates decline. Fewer studies have explored whether education exerts different effects on longitudinal changes within different cognitive domains. In the present study, we analyzed data from 1014 participants in the Victoria Longitudinal Study to examine the effects of education on composite scores reflecting verbal processing speed, working memory, verbal fluency, and verbal episodic memory. Using linear growth models adjusted for age at enrollment (range, 54-95 years) and gender, we found that years of education (range, 6-20 years) was strongly related to cognitive level in all domains, particularly verbal fluency. However, education was not related to rates of change over time for any cognitive domain. Results were similar in individuals older or younger than 70 at baseline, and when education was dichotomized to reflect high or low attainment. In this large longitudinal cohort, education was related to cognitive performance but unrelated to cognitive decline, supporting the hypothesis of passive cognitive reserve with aging.

Implications of Lifecourse Epidemiology for Research on Determinants of Adult Disease

Many diseases commonly associated with aging are now thought to have social and physiologic antecedents in early life. Understanding how the timing of exposure to early life risk factors influences later-life health may illuminate mechanisms driving adult health inequalities and identify possible points for effective interventions. Recognizing chronic diseases as developing across the lifecourse also has implications for the conduct of research on adult risk factors for disease. We review alternative conceptual models that describe how the timing of risk factor exposure relates to the development of disease. We propose some expansions of lifecourse models to improve their relevance for research on adult chronic disease, using the relationship between education and adult cognitive decline and dementia as an example. We discuss the important implications each of the lifecourse conceptual models has on study design, analysis, and interpretation of research on aging and chronic diseases. We summarize several research considerations implied by the lifecourse framework, including: advantages of analyzing change in function rather than onset of impairment; the pervasive challenge of survivor bias; the importance of controlling for possible confounding by early life conditions; and the likely heterogeneity in responses of adults to treatment.

Cognitive reserve

The concept of reserve has been proposed to account for the disjunction between the degree of brain damage and its clinical outcome. This paper attempts to produce a coherent theoretical account the reserve in general and of cognitive reserve in particular. It reviews epidemiologic data supporting the concept of cognitive reserve, with a particular focus of its implications for aging and dementia. It then focuses on methodologic issues that are important when attempting to elucidate the neural underpinnings of cognitive reserve using imaging studies, and reviews some of our group's work in order to demonstrate these issues.

The response-signal method reveals age-related changes in object working memory

Sixteen healthy young adults (ages 18-32) and 16 healthy older adults (ages 67-81) completed a delayed response task in which they saw the following visual sequence: memory stimuli (2 abstract shapes; 3,000 ms), a blank delay (5,000 ms), a probe stimulus of variable duration (one abstract shape; 125, 250, 500, 1,000, or 2,000 ms), and a mask (500 ms). Subjects decided whether the probe stimulus matched either of the memory stimuli; they were instructed to respond during the mask, placing greater emphasis on speed than accuracy. The authors used D. L. Hintzman & T. Curran's (1994) 3-parameter compound bounded exponential model of speed-accuracy tradeoff to describe changes in discriminability associated with total processing time. Group-level analysis revealed a higher rate parameter and a higher asymptote parameter for the young adult group, but no difference across groups in x-intercept. Proxy measures of cognitive reserve (Y. Stern et al., 2005) predicted the rate parameter value, particularly in older adults. Results suggest that in working memory, aging impairs both the maximum capacity for discriminability and the rate of information accumulation, but not the temporal threshold for discriminability.

Job demands and dementia risk among male twin pairs

BACKGROUND

Job characteristics may influence dementia risk, but some types of job complexity remain to be examined. Twin studies provide a useful methodology to examine job differences between pairs who share many environmental and genetic influences.

METHODS

Members of the NAS-NRC Twins Registry of World War II Veterans received a clinical evaluation for dementia and had job ratings from the Dictionary of Occupational Titles.

RESULTS

Cotwin-control models (n = 220 pairs) indicated lower dementia risk with greater job demands of reasoning, mathematics, language, and vocational training, with comparable results in case-control models (n=425 cases). These effects were significant among twin pairs discordant for 6 or more years, but not among those discordant between 3-5 years. Results were similar for Alzheimer's disease, and main effects were not further explained by zygosity or apolipoprotein E genotype.

CONCLUSIONS

Jobs that utilize data, academic skills, and extensive vocational training may protect against dementia; however, in twin pairs these effects only emerged among individuals who remained free of dementia several years after onset in their sibling.

Characterization of Japanese-American men with a single neocortical AD lesion type

Neocortical neuritic plaques (NP) and neurofibrillary tangles (NFT) are hallmarks of Alzheimer's disease (AD) and usually, both are present. The Honolulu-Asia Aging Study autopsy series includes a significant number of individuals with only one neocortical AD lesion type. These could represent an early phase of the AD process. If so, such individuals would be expected to share other clinical and pathological features of AD. We compared frequency of apolipoprotein epsilon E4 (APOE4) allele, average Braak stage, and burden of cerebral amyloid angiopathy (CAA) among the two single lesion type groups, a group without AD lesions, and groups with high and low frequencies of both AD lesions. Single AD lesion groups shared only the characteristics associated with their unique lesion type with the combined AD lesion group and did not have higher prevalence of dementia than the no AD lesion group. Only the NP+NFT group showed a "dose-response" relationship with greater probability of dementia with higher neocortical frequencies of either AD lesion. The single neocortical AD lesion groups do not appear to represent early AD.

Lifetime occupation and physical function: a prospective cohort study on persons aged 80 years and older living in a community

BACKGROUND

Several studies have reported predictors for loss of mobility and impairments of physical performance among frail elderly people.

AIM

To evaluate the relationship between lifetime occupation and physical function in persons aged 80 years or older.

METHODS

Data are from baseline evaluation of 364 subjects enrolled in the ilSIRENTE study (a prospective cohort study performed in a mountain community in Central Italy). Physical performance was assessed using the physical performance battery score, which is based on three timed tests: 4-metre walking speed, balance, and chair stand tests. Muscle strength was measured by hand grip strength. Lifetime occupation was categorised as manual or non-manual work.

RESULTS

Mean age of participants was 85.9 (SD 4.9) years. Of the total sample, 273 subjects (75%) had a history of manual work and 91 subjects (25%) a history of non-manual work. Manual workers had significant lower grip strength and physical performance battery score (indicating worse performance) than non-manual workers. After adjustment for potential confounders (including age, gender, education, depression, cognitive performance scale score, physical activity, number of diseases, hearing impairment, history of alcohol abuse, smoking habit, and haemoglobin level), manual workers had significantly worse physical function (hand grip strength: non-manual workers 32.5 kg, SE 1.4, manual workers 28.2 kg, SE 0.8; physical performance battery score: non-manual workers 7.1, SE 0.4, manual workers 6.1, SE 0.2).

CONCLUSIONS

A history of manual work, especially when associated with high physical stress, is independently associated with low physical function and muscle strength in older persons.

What provides cerebral reserve?

The cerebral reserve hypothesis is a heuristic concept used to explain apparent protection from the onset of cerebral disease and/or cognitive decline in old age. A significant obstacle when investigating the reserve hypothesis is the absence of baseline data with which to compare current cognitive status. We tested the influence of three hypothesized proxies of reserve (education, head size and occupational attainment [OCC]) in 92 volunteers born in 1921, whose cognitive function was measured at age 11 and 79 years, and who underwent brain MRI. The association between each proxy and old age cognitive function was tested, adjusting for variance contributed by childhood mental ability and detrimental age-related pathological changes measured using MRI. The results showed that education and OCC, but not total intracranial volume (TICV), contribute to cerebral reserve and help retain cognitive function in old age. Education was found to contribute between 5 and 6% of the variance found in old age memory function but was found to have no significant association with reasoning abilities. OCC was found to contribute around 5% of the variance found in old age memory function and between 6 and 8% of the variance found in old age reasoning abilities. We conclude that the intellectual challenges experienced during life, such as education and occupation, accumulate reserve and allow cognitive function to be maintained in old age.

Occupation during life and risk of dementia in French elderly community residents

OBJECTIVE

To determine whether principal occupation during life is a risk factor for incident Alzheimer's disease, vascular dementia, or dementia with parkinsonism.

METHODS

This study was carried out from the PAQUID (Personnes Agées QUID) cohort, an epidemiological study on normal and pathological aging after 65 years in the south west of France. At baseline, 2950 non-demented people living at home were identified and re-examined 1, 3, 5, 8, and 10 years later with identical standardised neurological and neuropsychological measures. Cox proportional hazards models with delayed entry were used, taking age as the time scale and adjusting for sex, education, tobacco, and wine consumption to estimate the risk ratio (RR) of incident dementia, Alzheimer's disease, vascular dementia, and dementia with parkinsonism associated with occupational category.

RESULTS

Of the 2950 subjects, 393 became demented, of whom 251 had Alzheimer's disease, 112 had vascular dementia, and 27 had dementia with parkinsonism. The risk of Alzheimer's disease was not related to a given occupation. However the risk of dementia with parkinsonism seemed to be increased in farmers in comparison with professionals and managerials, particularly among women (RR 7.47; 95%CI, 1.80-31.07).

CONCLUSION

The data suggest that occupation does not change the risk of Alzheimer's disease, which seems to be more influenced by cognitive abilities in childhood and adolescence than by occupation in adult life. However, being a farmer may increase the risk of dementia with parkinsonism among women; occupation could act by the way of differences in health behaviour or in exposure to environmental factors.