Asthma, eczema, rhinitis and the risk for dementia

From bite to brain: Neuro-immune interactions in food allergy

Immunoglobulin E (IgE)-mediated food allergies are reported to affect around 3.5% of children and 2.4% of adults, with symptoms varying in range and severity. While being the gold standard for diagnosis, oral food challenges are burdensome, and diagnostic tools based on specific IgE can be flawed. Furthering our understanding of the mechanisms behind food allergy onset, severity and persistence could help reveal immune profiles associated with the disease, to ultimately aid in diagnosis. Alterations to cytokine levels and immune cell ratios have been identified, though further research is needed to fully capture the heterogenous nature of food allergy. Moreover, the existence of such immune alterations also raises the question of potential wider systemic effects. For example, recent research has emphasised the existence and impact of neuro-immune interactions and implicated behavioural and neurological changes associated with food allergy. This review will provide an overview of such food allergy-driven neuro-immune interactions, with the aim of emphasising the importance of furthering our understanding of the immune mechanisms underlying IgE-mediated food allergy.

Potential association between obstructive lung diseases and cognitive decline

Introduction

Chronic obstructive lung diseases, such as asthma and COPD, appear to have a more extensive impact on overall functioning than previously believed. The latest data from clinical trials suggests a potential link between cognitive deterioration and chronic obstructive inflammatory lung disease. This raises the question of whether these diseases affect cognitive functions and whether any relevant biomarker may be identified.

Methods

This prospective observational study included 78 patients divided equally into asthma, COPD, and control groups (n=26, 27 and 25 respectively). The participants underwent identical examinations at the beginning of the study and after at least 12 months. The test battery comprised 16 questionnaires (11 self-rated, 5 observer-rated, assessing cognition and mental state), spirometry, and blood samples taken for PKA and CREB mRNA evaluation.

Results

A 2.3-fold increase in CREB mRNA was observed between examinations (p=0.014) for all participants; no distinctions were observed between the asthma, COPD, and control groups. Pooled, adjusted data revealed a borderline interaction between diagnosis and CREB expression in predicting MMSE (p=0.055) in COPD, CREB expression is also associated with MMSE (β=0.273, p=0.034) like with the other conducted tests (β=0.327, p=0.024) from COPD patients. No correlations were generally found for PKA, although one significant negative correlation was found between the first and second time points in the COPD group (β=-0.4157, p=0.049),.

Discussion

Chronic obstructive lung diseases, such as asthma and COPD, may have some linkage to impairment of cognitive functions. However, the noted rise in CREB mRNA expression might suggest a potential avenue for assessing possible changes in cognition, especially in COPD; such findings may reveal additional transcription factors linked to cognitive decline.

Causal Association Between Allergic Diseases and Dementia: Evidence from Multivariate Mendelian Randomization Study

Background

The link between allergic diseases and dementia remains controversial, and the genetic causality of this link is unclear.

Objective

This study investigated the causal relationship between allergic diseases and dementia using univariate and multivariate Mendelian randomization (MR) methods.

Methods

We selected genome-wide association studies including 66,645 patients with allergic diseases and 12,281 patients with dementia, with statistical datasets derived from the FinnGen Consortium of European origin. After a rigorous screening process for single nucleotide polymorphisms to eliminate confounding effects, MR estimation was performed mainly using the inverse variance weighting method and the MR-Egger method. Sensitivity analyses were performed using Cochran's Q test, MR-PRESSO test, MR Pleiotropy residuals and leave-one-out analysis.

Results

Univariate and multivariate MR together demonstrated a causal relationship between atopic dermatitis and reduced vascular dementia (VaD) risk (OR = 0.89, 95% CI: 0.81-0.99, p = 0.031; OR = 0.85, 95% CI: 0.76-0.95, p = 0.003). MVMR confirmed asthma was associated with a reduction in the risk of Alzheimer's disease (AD) (OR = 0.82, 95% CI: 0.71-0.94, p = 0.005) and may be associated with a reduction in the risk of VaD (OR = 0.80, 95% CI: 0.65-0.99, p = 0.042); allergic rhinitis may be causally associated with an increased risk of AD (OR = 1.16, 95% CI: 1.00-1.35, p = 0.046) and VaD (OR = 1.29, 95% CI: 1.03-1.62, p = 0.027). In sensitivity analyses, these findings were reliable.

Conclusions

MR methods have only demonstrated that allergic rhinitis dementia is associated with an increased risk of developing dementia. Previously observed associations between other allergic diseases and dementia may be influenced by comorbidities and confounding factors rather than causality.

Paranasal sinuses opacification on magnetic resonance imaging in relation to brain health in sporadic small vessel disease - Systematic review and pilot analysis

BACKGROUND

The paranasal sinus mucosal thickening, visible in magnetic resonance imaging (MRI), maybe a source of inflammation in microvessels, but its relationship with small vessel disease (SVD) is unclear. We reviewed the literature and analysed a sample of patients with sporadic SVD to identify any association between paranasal sinus opacification severity and SVD neuroimaging markers.

METHODS

We systematically reviewed MEDLINE and EMBASE databases up to April 2020 for studies on paranasal sinus mucosal changes in patients with SVD, cerebrovascular disease (CVD), and age-related neurodegenerative diseases. We analysed clinical and MRI data from 100 participants in a prospective study, the Mild Stroke Study 3 (ISRCTN 12113543) at 1-3, 6 and 12 months following a minor stroke to test key outcomes from the literature review. We used multivariate linear regression to explore associations between modified Lund-Mackay (LM) scores and brain, white matter hyperintensities (WMH), enlarged perivascular spaces (PVS) volumes at each time point, adjusted for baseline age, sex, diabetes, hypercholesterolaemia, hypertension and smoking.

RESULTS

The literature review, after screening 3652 publications, yielded 11 primary studies, for qualitative synthesis with contradictory results, as positive associations/higher risk from 5/7 CVD studies were contradicted by the two studies with largest samples, and data from dementia studies was equally split in their outcome. From the pilot sample of patients analysed (female N = 33, mean age 67.42 (9.70) years), total LM scores had a borderline negative association with PVS in the centrum semiovale at baseline and 6 months (B = -0.25, SE = 0.14, p = 0.06) but were not associated with average brain tissue, WMH or normal-appearing white matter volumes.

CONCLUSION

The inconclusive results from the literature review and empirical study justify larger studies between PVS volume and paranasal sinuses opacification in patients with sporadic SVD.

Impact of asthma on the brain: evidence from diffusion MRI, CSF biomarkers and cognitive decline

Chronic systemic inflammation increases the risk of neurodegeneration, but the mechanisms remain unclear. Part of the challenge in reaching a nuanced understanding is the presence of multiple risk factors that interact to potentiate adverse consequences. To address modifiable risk factors and mitigate downstream effects, it is necessary, although difficult, to tease apart the contribution of an individual risk factor by accounting for concurrent factors such as advanced age, cardiovascular risk, and genetic predisposition. Using a case-control design, we investigated the influence of asthma, a highly prevalent chronic inflammatory disease of the airways, on brain health in participants recruited to the Wisconsin Alzheimer's Disease Research Center (31 asthma patients, 186 non-asthma controls, aged 45-90 years, 62.2% female, 92.2% cognitively unimpaired), a sample enriched for parental history of Alzheimer's disease. Asthma status was determined using detailed prescription information. We employed multi-shell diffusion weighted imaging scans and the three-compartment neurite orientation dispersion and density imaging model to assess white and gray matter microstructure. We used cerebrospinal fluid biomarkers to examine evidence of Alzheimer's disease pathology, glial activation, neuroinflammation and neurodegeneration. We evaluated cognitive changes over time using a preclinical Alzheimer cognitive composite. Using permutation analysis of linear models, we examined the moderating influence of asthma on relationships between diffusion imaging metrics, CSF biomarkers, and cognitive decline, controlling for age, sex, and cognitive status. We ran additional models controlling for cardiovascular risk and genetic risk of Alzheimer's disease, defined as a carrier of at least one apolipoprotein E (APOE) ε4 allele. Relative to controls, greater Alzheimer's disease pathology (lower amyloid-β42/amyloid-β40, higher phosphorylated-tau-181) and synaptic degeneration (neurogranin) biomarker concentrations were associated with more adverse white matter metrics (e.g. lower neurite density, higher mean diffusivity) in patients with asthma. Higher concentrations of the pleiotropic cytokine IL-6 and the glial marker S100B were associated with more salubrious white matter metrics in asthma, but not in controls. The adverse effects of age on white matter integrity were accelerated in asthma. Finally, we found evidence that in asthma, relative to controls, deterioration in white and gray matter microstructure was associated with accelerated cognitive decline. Taken together, our findings suggest that asthma accelerates white and gray matter microstructural changes associated with aging and increasing neuropathology, that in turn, are associated with more rapid cognitive decline. Effective asthma control, on the other hand, may be protective and slow progression of cognitive symptoms.

Hidden Comorbidities in Asthma: A Perspective for a Personalized Approach

Bronchial asthma is the most frequent inflammatory non-communicable condition affecting the airways worldwide. It is commonly associated with concomitant conditions, which substantially contribute to its burden, whether they involve the lung or other districts. The present review aims at providing an overview of the recent acquisitions in terms of asthma concomitant systemic conditions, besides the commonly known respiratory comorbidities. The most recent research has highlighted a number of pathobiological interactions between asthma and other organs in the view of a shared immunological background underling different diseases. A bi-univocal relationship between asthma and common conditions, including cardiovascular, metabolic or neurodegenerative diseases, as well as rare disorders such as sickle cell disease, α1-Antitrypsin deficiency and immunologic conditions with hyper-eosinophilia, should be considered and explored, in terms of diagnostic work-up and long-term assessment of asthma patients. The relevance of that acquisition is of utmost importance in the management of asthma patients and paves the way to a new approach in the light of a personalized medicine perspective, besides targeted therapies.

Associations of Lung Function Decline with Risks of Cognitive Impairment and Dementia: A Meta-Analysis and Systematic Review

BACKGROUND

There are controversies surrounding the effects of lung function decline on cognitive impairment and dementia.

OBJECTIVE

We conducted a meta-analysis and systematic review to explore the associations of lung function decline with the risks of cognitive impairment and dementia.

METHODS

The PubMed, EMBASE, and the Cochrane Library were searched to identify prospective studies published from database inception through January 10, 2023. We pooled relative risk (RR) and 95% confidence intervals (CI) using random-effects models. The Egger test, funnel plots, meta-regression, sensitivity, and subgroup analyses were conducted to detect publication bias and investigate the source of heterogeneity.

RESULTS

Thirty-three articles with a total of 8,816,992 participants were subjected to meta-analysis. Poorer pulmonary function was associated with an increased risk of dementia (FEV: RR = 1.25 [95% CI, 1.17-1.33]; FVC: RR = 1.40 [95% CI, 1.16-1.69]; PEF: RR = 1.84 [95% CI, 1.37-2.46]). The results of the subgroup analyses were similar to the primary results. Individuals with lung diseases had a higher combined risk of dementia and cognitive impairment (RR = 1.39 [95% CI, 1.20-1.61]). Lung disease conferred an elevated risk of cognitive impairment (RR = 1.37 [95% CI, 1.14-1.65]). The relationship between lung disease and an increased risk of dementia was only shown in total study participants (RR = 1.32 [95% CI, 1.11-1.57]), but not in the participants with Alzheimer's disease (RR = 1.39 [95% CI, 1.00-1.93]) or vascular dementia (RR = 2.11 [95% CI, 0.57-7.83]).

CONCLUSION

Lung function decline was significantly associated with higher risks of cognitive impairment and dementia. These findings might provide implications for the prevention of cognitive disorders and the promotion of brain health.

Allergic Diseases and Risk of Incident Dementia and Alzheimer's Disease

OBJECTIVE

To examine the associations between the allergic triad (asthma, allergic rhinitis, atopic dermatitis) and risk of dementia.

METHODS

Participants comprised 6,785,948 adults aged ≥40 years who participated in a national health examination in 2009 without any history of dementia before baseline. From 2009 to 2017, we prospectively investigated the associations between physician-diagnosed allergic diseases and risk of incident dementia (all-cause, Alzheimer's disease [AD], vascular dementia [VaD]) ascertained using national health insurance claims data.

RESULTS

During 8.1 years of follow-up, 260,705 dementia cases (195,739 AD, 32,789 VaD) were identified. Allergic diseases were positively associated with dementia risk. Compared with individuals without allergic diseases, multivariable hazard ratios (HRs) of all-cause dementia were 1.20 (95% confidence interval [CI] 1.19-1.22) in those with asthma, 1.10 (95% CI 1.09-1.12) with allergic rhinitis, 1.16 (95% CI 1.11-1.21) with atopic dermatitis, and 1.13 (95% CI 1.12-1.14) with any of these allergies. Similarly, individuals with any of the allergic triad had a higher risk of AD (HR 1.16, 95% CI 1.14-1.17) and VaD (HR 1.04; 95% CI 1.01-1.06) than those without any allergic disease. As the number of comorbid allergic diseases increased, the risk of dementia increased linearly (P_trend  ≤ 0.002). Compared with individuals without allergies, those with all three allergic diseases had substantially increased risk of all-cause dementia (HR 1.54, 95% CI 1.35-1.75), AD (HR 1.46; 95% CI 1.25-1.70), and VaD (HR 1.99, 95% CI 1.44-2.75).

INTERPRETATION

Asthma, allergic rhinitis, and atopic dermatitis were significantly associated with increased risk of all-cause dementia and subtypes, with dose-effect relationships with the severity of allergic diseases. ANN NEUROL 2023;93:384-397.

The link between cutaneous inflammation and cognitive impairment

Cognitive impairment is a symptom of neurological disorders, including dementia and Alzheimer's disease; and mild cognitive impairment can be a precursor of both disorders. Aged humans and animal models with other systemic disorders, such as cardiovascular diseases and diabetes, display a higher incidence of cognitive decline. Epidemiological studies have shown that the incidence of cognitive impairment also is higher in subjects with certain inflammatory skin disorders, including psoriasis and chronic eczematous dermatitis. Chronologically aged individuals exhibit increased cutaneous inflammation and elevated circulating cytokine levels, linked to alterations in epidermal function, which itself can induce cutaneous inflammation. Conversely, strategies that improve epidermal function can lower cytokine levels in both the skin and circulation. Thus, it seems likely that epidermal dysfunction could contribute, at least in part, to the development of chronic low-grade inflammation, also termed 'inflammaging', in the elderly. The evidence of cognitive impairment in patients with inflammatory dermatoses suggests a link between cutaneous inflammation and cognitive impairment. Because of the pathogenic role of epidermal dysfunction in ageing-associated cutaneous inflammation, improvements in epidermal function could be an alternative approach for mitigation of the ageing-associated decline in cognitive function.

Adult atopic eczema and the risk of dementia: A population-based cohort study

BACKGROUND

Chronic inflammatory conditions have been linked to dementia, but little is known about the role of atopic eczema, an inflammatory condition recently recognized to be common among older adults.

OBJECTIVE

To determine whether active atopic eczema is associated with incident dementia.

METHODS

A longitudinal cohort study of 1,767,667 individuals aged 60 to 99 years registered with The Health Improvement Network, a primary care cohort in the United Kingdom. The diagnoses of atopic eczema and dementia were identified using medical record codes.

RESULTS

The incidence of dementia was 57 per 10,000 person-years among those with atopic eczema during follow-up (12.1% of the population) compared with 44 per 10,000 person-years in the control group. This translated to a 27% increased risk of dementia (hazard ratio, 1.27; 95% CI, 1.23-1.30) in adjusted Cox proportional hazard models. Similar associations were observed in subgroup analyses of vascular dementia and Alzheimer's disease. The association persisted after additionally adjusting for the use of systemic corticosteroids (hazard ratio, 1.29; 95% CI, 1.26-1.33) and potential mediators (hazard ratio, 1.19; 95% CI, 1.16-1.22). More severe eczema was associated with a higher risk of dementia.

LIMITATIONS

Lack of detailed data on severity.

CONCLUSION

Atopic eczema was associated with a small but increased risk of incident dementia. The association increased with the severity of atopic eczema.

TAK-242 ameliorates olfactory dysfunction in a mouse model of allergic rhinitis by inhibiting neuroinflammation in the olfactory bulb

OBJECTIVE

Olfactory dysfunction (OD) is a common symptom of allergic rhinitis (AR) that can seriously affect patient quality of life; however, the associated pathogenesis remains unclear. This study aimed to explore the relationship between OD and damage of the olfactory bulb (OB) in allergic rhinitis (AR). The therapeutic potential of TAK-242, a selective TLR4 inhibitor, was evaluated for OD.

METHOD

An AR mouse model was established with ovalbumin (OVA) to test the olfactory function of AR mice using the buried food pellet test (BFPT). Mice with OD were intraperitoneally injected with TAK-242 or 1% DMSO (vehicle). Immunohistochemistry was used to detect microglia and astrocyte activation in the OB. TUNNEL staining was performed to detect apoptosis in the OB. Proteins in the TLR4 signaling pathway were detected by Western blot. The level of proinflammatory factor mRNA in the OB was determined by RT-PCR.

RESULT

Neuroinflammation was observed in the OB of the OD group, as evidenced by glial cell activation and increased proinflammatory factor expression. The number of apoptotic cells was significantly increased in the OB of the OD group. The expression of TLR4, MyD88, and p-NF-κBp65 was significantly up-regulated in the OB of the OD group. TAK-242 treatment significantly reduced the level of IL-1β, IL-6, and TNF-α mRNA expression, as well as activation of microglia and astrocytes in the OB tissues.

CONCLUSION

TAK-242 improve olfactory function in AR mice mainly by reducing neuroinflammation and apoptosis in the OB, which may be related to blocking the TLR4/MyD88/NF-κB signaling pathway.

Chronic Airway Allergy Induces Pro-Inflammatory Responses in the Brain of Wildtype Mice but Not 3xTgAD Mice

The effects of systemic inflammation on the pathogenesis of Alzheimer's disease (AD) are not clarified, both beneficial and deleterious effects being reported. Allergy is accompanied by a systemic inflammatory response and some epidemiological studies have reported a positive association between a history of allergy/asthma and dementia. To investigate whether chronic airway allergy influences the inflammatory status in the brain, AD-like pathology, and behaviour in relation to AD, we induced chronic airway allergy in triple transgenic AD (3xTgAD) and wildtype (WT) mice by repeated exposure to ovalbumin (OVA) as allergen. Behavioural tests relevant for hippocampus-dependent behaviour were performed. We found that allergy significantly increased the brain levels of immunoglobulin (Ig) G, IgE. In 3xTgAD mice, allergy increased the levels of decay accelerating factor and decreased the phosphorylation of p38. In contrast, allergy increased the levels of interleukin (IL)-1β and complement component 1q (C1q) in WT mice. Bronchoalveolar lavage fluid analysis confirmed eosinophilia in both genotypes, but the basal levels of eosinophils were lower in 3xTgAD mice. In summary, allergy induced predominantly anti-inflammatory effects in 3xTgAD mice, and pro-inflammatory effects in WT mice, thus being another potential factor to be considered when studying AD pathogenesis.

Chronic Respiratory Disease and Cognitive Impairment in Older Mexican Adults

Background

Cognitive impairment has emerged as an important concern in clinical practice in aging population. Several comorbid factors contribute to etiopathogenesis; one disease of interest is chronic respiratory disease.

Aim

The aim of this study is to investigate the association of chronic respiratory disease with risk of cognitive impairment in older Mexicans.

Materials and Methods

Data were obtained from 2782 Mexicans, aged ≥60 years, enrolled in waves I (2001) and III (2012) of the Mexican Health and Aging Study, a prospective cohort of nationally representative sample of older Mexicans. Participants' self-reported responses were used to categorize them into having respiratory disease or not. Study outcome included participants categorized into "cognitively impaired" or "cognitively normal" groups. Multivariable logistic regression models were used to investigate the relationship.

Results

Overall, 16% of cohort participants reported cognitively impaired at Wave III. Compared with older Mexicans without chronic respiratory disease diagnosis, those diagnosed were not significantly associated with risk of cognitive impairment [adjusted odds ratio (OR): 0.94, 95% confidence interval (CI): 0.58-1.58].

Conclusion

Chronic respiratory disease is not significantly associated with risk of cognitive impairment in older Mexican adults.

Prevalence of asthma in patients with atopic dermatitis: A systematic review and meta-analysis

BACKGROUND

It is well established that asthma is common in patients with atopic dermatitis (AD).

OBJECTIVES

We performed a systematic review and meta-analysis to determine the prevalence of asthma and respiratory symptoms in individuals with AD as well as the association between AD and asthma.

METHODS

At least 2 authors independently searched the medical databases PubMed, EMBASE, LILACS, and SCOPUS for all English-language studies with data on asthma prevalence among patients with AD or the association between AD and asthma. Pooled odds ratios with 95% confidence intervals (CIs) and pooled proportions were estimated with random-effects models. The Newcastle-Ottawa scale was used to assess study quality.

RESULTS

The search yielded 39,503 articles. Of these, 213 studies were included in a quantitative analysis. The overall pooled prevalence of asthma was 25.7% (95% CI, 23.7-27.7) in patients with AD and 8.1% (95% CI, 7.0-9.4) among reference individuals. There was a significant association between AD and asthma when compared with reference individuals (odds ratio, 3.03; 95% CI, 2.64-3.47).

LIMITATIONS

The definitions of AD and asthma differed across the included studies and varied from self-report to physician diagnosed.

CONCLUSIONS

Asthma is a common comorbidity of AD. Physicians should be cognizant of this relationship and address asthma symptoms in their patients.

Respiratory Disease and Lower Pulmonary Function as Risk Factors for Dementia: A Systematic Review With Meta-analysis

BACKGROUND

In addition to affecting the oxygen supply to the brain, pulmonary function is a marker of multiple insults throughout life (including smoking, illness, and socioeconomic deprivation). In this meta-analysis of existing longitudinal studies, the hypothesis that lower pulmonary function and respiratory illness are linked to an elevated risk of dementia was tested.

METHODS

A systematic review was conducted of longitudinal studies using PubMed until April 1, 2019, and, where possible, results were pooled in random effects meta-analyses.

RESULTS

Ten studies relating pulmonary function to later dementia risk and 11 studies of respiratory illness and dementia (including one that assessed both factors) were identified. The lowest quartile of FEV₁ compared with the highest was associated with a 1.4-fold (hazard ratio [HR], 1.46; 95% CI, 0.77-2.75) increased dementia risk (N_total = 62,209; two studies). A decrease of 1 SD in FEV₁ was associated with a 28% increase in dementia risk (HR, 1.28; 95% CI, 1.03-1.60; N_total = 67,505; six studies). Respiratory illness was also associated with increased dementia risk to a similar degree (pooled HR, 1.54; 95% CI, 1.30-1.81; N_total = 288,641; 11 studies).

CONCLUSIONS

Individuals with poor pulmonary function experience an increased risk of dementia. The extent to which the association between poor pulmonary function and dementia is causal remains unclear and requires examination.

Risk of neurodegenerative dementia in asthma patients: a nested case-control study using a national sample cohort

OBJECTIVES

This study investigated the risk of neurodegenerative dementia following asthma.

DESIGN

A nested case-control study SETTING: The ≥60-year-old population was selected from the Korean Health Insurance Review and Assessment Service - National Sample Cohort from 2002 to 2013.

PARTICIPANTS AND INTERVENTIONS

The 11 442 dementia cases were matched with 45 768 control cases for age, sex, income, region of residence, hypertension, diabetes and dyslipidaemia. Asthma was classified using International Classification of Disease-10 (ICD-10) codes (J45 and J46) and medication history. Dementia was identified based on ICD-10 codes (G30 and F00).

PRIMARY AND SECONDARY OUTCOME MEASURES

The ORs of a previous history of asthma in patients with dementia were analysed using conditional logistic regression analysis stratified for age, sex, income, region of residence, hypertension, diabetes and dyslipidaemia. Subgroup analysis was performed according to age and sex.

RESULTS

Overall, 22.6% (2587/11 442) and 22.3% (10 229/45 768) of the cases in the dementia and control groups, respectively, had a previous history of asthma. The OR for asthma in the dementia group was not higher than that in the control group (adjusted OR=0.97, 95% CI 0.92 to 1.02, p=0.207). All age and sex subgroups demonstrated consistent results.

CONCLUSIONS

Asthma was not related to an increased risk of dementia.

Influence of PM2.5 Exposure Level on the Association between Alzheimer's Disease and Allergic Rhinitis: A National Population-Based Cohort Study

Alzheimer's disease (AD) is an irreversible neurodegenerative disease that leads to dementia, health impairment, and high economic cost. Allergic rhinitis (AR) is a chronic inflammatory and allergic disease of the respiratory system that leads to health problems and has major effects on the daily lives of patients and their caregivers. Particulate matter (PM) refers to air pollutants 2.5 μm or less in diameter that are a source of concern because of their role in numerous diseases, including AR and other neurodegenerative diseases. To date, no study has demonstrated how PM_2.5 exacerbates AR and results in AD. We conducted a national population-based cohort study by obtaining patient data from the National Health Insurance Research Database of Taiwan for the 2008-2013 period. PM_2.5 concentration data were obtained from the ambient air quality monitoring network established by the Environmental Protection Administration of Taiwan. Monthly PM_2.5 exposure levels were categorized into quartiles from Q1-Q4. The Cox proportional hazards analysis, after adjusting for age, sex, low income, and urbanization level, revealed that patients with AR had an elevated risk of developing AD (hazard ratio (HR): 2.008). In addition, the cumulative incidence of AD in the AR group was significantly higher than in the comparison group. The PM_2.5 levels at Q2-Q4 (crude HR: 1.663-8.315; adjusted HR: 1.812-8.981) were stratified on the basis of the PM_2.5 exposure group and revealed that AR patients exposed to PM_2.5 are significantly prone to develop AD. In addition, the logistic regression analyses, after adjustment, demonstrated that an increase in the PM_2.5 exposure level at Q2-Q4 (adjusted odds ratio (OR): 2.656-5.604) increased the risk of AR in AD patients. In conclusion, an increased PM_2.5 exposure level could be correlated with AR, which could in turn cause AD. AR increased the risk of AD, in which exposure to PM_2.5 increases the higher probability of AD.

Exposure to formaldehyde and diisononyl phthalate exacerbate neuroinflammation through NF-κB activation in a mouse asthma model

Diisononyl phthalate (DINP) and formaldehyde both are associated with asthma and allergies. However, it is unclear about the adverse effect of DINP and formaldehyde exposure on the brain for asthma patients. Here, we determined the effect of DINP and/or formaldehyde exposure on neuroinflammation in brain by a murine asthma model and investigated the underlying mechanisms. Mice were exposed to formaldehyde and/or DINP and sensitization with ovalbumin. The results show that exposure to formaldehyde and/or DINP not only exacerbated allergic asthma-like symptoms, but also promoted neuroinflammation in brain. The incrassation of the airway wall and exacerbation of neuroinflammation were more obviously when mice were subjected to a combined exposure to DINP and formaldehyde. Exposure to DINP and/or formaldehyde enhances oxidative stress and the activation of NF-κB in the prefrontal cortex of mouse asthma model. Exposure to DINP and/or formaldehyde also induced an increase in IL-1β, IL-17, and NGF. Blocking oxidative stress by administering melatonin or inhibiting NF-κB activation by treatment with Dehydroxymethylepoxyquinomicin effectively prevented increasing the levels IL-1β, IL-17 and nerve growth factor. The data indicated that DINP and/or formaldehyde exposure promoted neuroinflammation in the brain through enhanced oxidative stress and activation of NF-κB in a mouse asthma model.

Air pollution, aeroallergens and suicidality: a review of the effects of air pollution and aeroallergens on suicidal behavior and an exploration of possible mechanisms

OBJECTIVE

Risk factors for suicide can be broadly categorized as sociodemographic, clinical and treatment. There is interest in environmental risk and protection factors for suicide. Emerging evidence suggests a link between environmental factors in the form of air pollution and aeroallergens in relation to suicidality.

METHODS

Herein, we conducted a systematic review of 15 articles which have met inclusion criteria on the aforementioned effects.

RESULTS

The majority of the reviewed articles reported an increased suicide risk alongside increased air pollutants or aeroallergens (i.e. pollen) increase; however, not all environmental factors were explored equally. In specific, studies that were delimited to evaluating particulate matter (PM) reported a consistent association with suicidality. We also provide a brief description of putative mechanisms (e.g. inflammation and neurotransmitter dysregulation) that may mediate the association between air pollution, aeroallergens and suicidality.

CONCLUSION

Available evidence suggests that exposure to harmful air quality may be associated with suicidality. There are significant public health implications which are amplified in regions and countries with greater levels of air pollution and aeroallergens. In addition, those with atopic sensitivity may represent a specific subgroup that is at risk.

Comorbidities in adults with asthma: Population-based cross-sectional analysis of 1.4 million adults in Scotland

BACKGROUND

Comorbidity in people with asthma can significantly increase asthma morbidity and lower adherence to asthma guidelines.

OBJECTIVE

The objective of this study was to comprehensively measure the prevalence of physical and mental health comorbidities in adults with asthma using a large nationally representative population.

METHODS

Cross-sectional analysis of routine primary care electronic medical records for 1 424 378 adults in the UK, examining the prevalence of 39 comorbidities in people with and without asthma, before and after adjustment for age, sex, social deprivation and smoking status using logistic regression.

RESULTS

Of 39 comorbidities measured, 36 (92%) were significantly more common in adults with asthma; 62.6% of adults with asthma had ≥1 comorbidity vs 46.2% of those without, and 16.3% had ≥4 comorbidities vs 8.7% of those without. Comorbidities with the largest absolute increase in prevalence in adults with asthma were as follows: chronic obstructive pulmonary disease (COPD) (13.4% vs 3.1%), depression (17.3% vs 9.1%), painful conditions (15.4% vs 8.4%) and dyspepsia (10.9% vs 5.2%). Comorbidities with the largest relative difference in adults with asthma compared to those without were as follows: COPD (adjusted odds ratio [aOR] 5.65, 95% CI 5.52-5.79), bronchiectasis (aOR 4.65, 95% CI 4.26-5.08), eczema/psoriasis (aOR 3.30, 95% CI 3.14-3.48), dyspepsia (aOR 2.20, 95% CI 2.15-2.25) and chronic sinusitis (aOR 2.12, 95% CI 1.99-2.26). Depression and anxiety were more common in adults with asthma (aOR 1.60, 95% CI 1.57-1.63, and aOR 1.53, 95% CI 1.48-1.57, respectively).

CONCLUSIONS AND CLINICAL RELEVANCE

Physical and mental health comorbidities are the norm in adults with asthma. Appropriate recognition and management should form part of routine asthma care.

Allergic rhinitis, bronchial asthma and other allergies in patients with Alzheimer's disease: unnoticed issue

INTRODUCTION

Allergic diseases are becoming more prevalent in elderly patients. Allergic diseases have been observed in patients with Alzheimer's disease (AD). The prevalence of atopic bronchial asthma, allergic rhinitis and atopic dermatitis was analyzed in such elderly Polish population.

AIM

Analysis of the presence of allergic diseases in the patients with AD in Poland, including asthma, allergic rhinoconjunctivitis and atopic dermatitis.

MATERIAL AND METHODS

The recruitment of subjects with AD was conducted at 6 sites representative of Polish rural and urban areas, and 1060 subjects with a mean age of 69.2 ±5.1 years were screened. Medical examinations, an original questionnaire, skin prick testing for common aeroallergens and appropriate serum-specific IgE assays were performed.

RESULTS

Probable atopy was diagnosed in 234 (22.1%) analyzed patients, including 127 women (21.5% of women) and 234 men (22.8% of men). The average prevalence associated with age and sex in this population for bronchial asthma was 2.9%, atopic dermatitis/eczema was 0.6%, seasonal allergic rhinitis was 6.6%, perennial allergic rhinitis was 11.1% and polymorphous atopic disease was 4.4%. The most frequent positive results were recorded for the following allergens: mixed grass, Dermatophagoides pteronyssinus, Dermatophagoides farinae and Alternaria.

CONCLUSIONS

One-fifth of diagnosed patients with AD have allergic disease requiring treatment.

Influence of Allergy on Immunoglobulins and Amyloid-β in the Cerebrospinal Fluid of Patients with Alzheimer's Disease

BACKGROUND

Peripheral inflammation has been suggested to influence the development of Alzheimer's disease (AD). Elevated levels of pro-inflammatory markers in the plasma of patients with AD indicate that a systemic pro-inflammatory status occurs concomitantly with inflammatory changes in the brain.

OBJECTIVE

To investigate whether allergy influences the levels of immunoglobulins (Ig) and of pro- and anti-inflammatory cytokines in the serum and cerebrospinal fluid (CSF) from patients with AD, mild cognitive impairment (MCI), and subjective cognitive impairment (SCI).

METHODS

IgA, IgG, and its subclasses, IgM, and cytokines were analyzed in CSF and serum from patients with SCI, MCI, and AD, with or without allergy. The relation between allergy and Mini-Mental State Examination (MMSE) scores, and between allergy and CSF biomarkers for AD (phosphorylated (p)-tau, total (t)-tau, amyloid-β 42 (Aβ₄₂), were analyzed.

RESULTS

In MCI, the CSF levels of IgG2 were lower in allergic patients, and in AD, the levels of IgA and the IgG1/total IgG ratio were lower in allergic patients, compared to patients without allergy. MCI subjects with allergy had higher serum IgM levels compared to those without allergy. CSF levels of Aβ₄₂ were lower and MMSE scores were higher in AD patients with allergy than in those without allergy.

CONCLUSIONS

The presence of allergy was associated with seemingly beneficial effects on AD as suggested by higher Aβ₄₂ levels in CSF, and higher MMSE scores. Higher IgM levels and lower other Ig classes suggest that allergy may influence senescence of the immune response.

Allergy Enhances Neurogenesis and Modulates Microglial Activation in the Hippocampus

Allergies and their characteristic T_H2-polarized inflammatory reactions affect a substantial part of the population. Since there is increasing evidence that the immune system modulates plasticity and function of the central nervous system (CNS), we investigated the effects of allergic lung inflammation on the hippocampus—a region of cellular plasticity in the adult brain. The focus of the present study was on microglia, the resident immune cells of the CNS, and on hippocampal neurogenesis, i.e., the generation of new neurons. C57BL/6 mice were sensitized with a clinically relevant allergen derived from timothy grass pollen (Phl p 5). As expected, allergic sensitization induced high serum levels of allergen-specific immunoglobulins (IgG1 and IgE) and of T_H2 cytokines (IL-5 and IL-13). Surprisingly, fewer Iba1⁺ microglia were found in the granular layer (GL) and subgranular zone (SGZ) of the hippocampal dentate gyrus and also the number of Iba1⁺MHCII⁺ cells was lower, indicating a reduced microglial surveillance and activation in the hippocampus of allergic mice. Neurogenesis was analyzed by labeling of proliferating cells with bromodeoxyuridine (BrdU) and determining their fate 4 weeks later, and by quantitative analysis of young immature neurons, i.e., cells expressing doublecortin (DCX). The number of DCX⁺ cells was clearly increased in the allergy animals. Moreover, there were more BrdU⁺ cells present in the hippocampus of allergic mice, and these newly born cells had differentiated into neurons as indicated by a higher number of BrdU⁺NeuN⁺ cells. In summary, allergy led to a reduced microglia presence and activity and to an elevated level of neurogenesis in the hippocampus. This effect was apparently specific to the hippocampus, as we did not observe these alterations in the subventricular zone (SVZ)/olfactory bulb (OB) system, also a region of high cellular plasticity and adult neurogenesis.

Atopy and cause-specific mortality

BACKGROUND

Atopy is the familial or personal propensity to develop immunoglobulin E (IgE) antibodies against common environmental allergens and is associated with high risk of allergic disease. It has been proposed that atopy may have effects on risk of cardiovascular disease and cancer.

OBJECTIVES

We investigated the association of atopy with all-cause and cause-specific mortality.

METHODS

We included a total of 14 849 individuals from five Danish population-based cohorts with measurements of atopy defined as serum-specific IgE positivity against inhalant allergens. Participants were followed by linkage to the Danish Registry of Causes of Death to obtain information on mortality status and cause of death (median follow-up time 11.3 years). The relative mortality risk was estimated by Cox regression and expressed as hazard ratios, HRs (95% confidence intervals, CIs).

RESULTS

A total of 1776 person died during follow-up. The mortality risk for atopics vs. non-atopics was: for all-cause mortality (HR = 1.03, 95% CI: 0.90, 1.17); neoplasms (HR = 0.86, 95% CI: 0.69, 1.06); endocrine, nutritional and metabolic disorders (HR = 1.48, 95% CI: 0.71, 3.08); mental and behavioural disorders (HR = 2.26, 95% CI: 1.18, 4.30); diseases of the nervous system (HR = 1.36, 95% CI: 0.65, 2.87); diseases of the circulatory system (HR = 1.00, 95% CI: 0.78, 1.29); diseases of the respiratory system (HR = 0.94, 95% CI: 0.55, 1.60); and diseases of the digestive system (HR = 1.75, 95% CI: 1.03, 2.98).

CONCLUSIONS & CLINICAL RELEVANCE

We found no statistically significant association between atopy and all-cause mortality. However, atopy was associated with a significantly higher risk of dying from mental and behavioural disorders and gastrointestinal diseases, particularly liver diseases, and a lower risk of dying from breast cancer, but these associations were not statistically significant when applying the Bonferroni adjusted significance level. Further studies are needed to confirm our findings.

Lung disease as a determinant of cognitive decline and dementia

Almost 40 million people currently live with dementia but this is estimated to double over the next 20 years; despite this, research identifying modifiable risk factors is scarce. There is increasing evidence that cognitive impairment is more frequent in those with chronic lung disease than those without. Chronic obstructive pulmonary disease affects 210 million people, with cognitive impairment present in 60% of certain populations. Co-morbid cognitive dysfunction also appears to impact on important outcomes such as quality of life, hospitalisation and survival. This review summarises the evidence of an association between cognition, impaired lung function and obstructive lung disease. It goes on to examine the contribution of neuro-imaging to our understanding of the underlying pathophysiology. While the mechanisms of brain pathology and cognitive impairment are likely to be complex and multi-factorial, there is evidence to suggest a key role for occult cerebrovascular damage independent of traditional vascular risk factors, including smoking.

Adult asthma increases dementia risk: a nationwide cohort study

BACKGROUND

Studies on the association between adult asthma and dementia are few. We investigated the risk of dementia in patients diagnosed with adult asthma compared with that of people without asthma who were age and sex matched to the study patients.

METHODS

We used data from the National Health Insurance Research Database. A total of 12 771 patients with newly diagnosed asthma between 2001 and 2003 were evaluated and 51 084 people without asthma were used as the comparison cohort. Cox proportional hazard regression analysis was used to measure the HR of dementia for the asthmatic cohort, compared with that of the non-asthmatic cohort.

RESULTS

The HR of dementia was 1.27 (95% confidence interval (CI) 1.15 to 1.41) for the asthmatic cohort, compared with the non-asthmatic cohort after adjusting for age, sex, comorbidities, annual outpatient department visits and medicine used. The HR of dementia development increased substantially as frequency of asthma exacerbation and hospitalisation increased.

CONCLUSIONS

This nationwide cohort study suggests that the risk of dementia development is significantly increased in patients with asthma compared with that of the general population. In addition, dementia risk increases substantially with asthma exacerbation and hospitalisation frequency increases.

Risk of dementia among patients with asthma: a nationwide longitudinal study

BACKGROUND

Previous studies have suggested an association between asthma and dementia, but the results are still inconsistent.

METHODS

Using the Taiwan National Health Insurance Database, we enrolled 11,030 participants aged more than 45 years with asthma and 44,120 (1:4) age-/sex-matched controls between 1998 and 2008, and followed them to the end of 2011. Cases of any dementia or Alzheimer's disease that developed during the follow-up period were identified.

RESULTS

Asthma was associated with an increased risk of developing any dementia [hazard ratio (HR): 2.17, 95% confidence interval (CI): 1.87-2.52] and Alzheimer's disease (HR: 2.62, 95% CI: 1.71-4.02). Stratified by age, both asthma in midlife (>45 years and <65 years) and in late life (≥65 years) was associated with a greater likelihood of any dementia (HR: 2.48, 95% CI: 1.80-3.41; HR: 2.06, 95% CI: 1.74-2.44).

DISCUSSION

Asthma in midlife and in late life increased the risk of developing any dementia and Alzheimer's disease. The underlying mechanisms between asthma and dementia require further investigation.

IVIg protects the 3xTg-AD mouse model of Alzheimer's disease from memory deficit and Aβ pathology

Background

Intravenous immunoglobulin (IVIg) is currently in clinical study for Alzheimer’s disease (AD). However, preclinical investigations are required to better understand AD-relevant outcomes of IVIg treatment and develop replacement therapies in case of unsustainable supply.

Methods

We investigated the effects of IVIg in the 3xTg-AD mouse model, which reproduces both Aβ and tau pathologies. Mice were injected twice weekly with 1.5 g/kg IVIg for 1 or 3 months.

Results

IVIg induced a modest but significant improvement in memory in the novel object recognition test and attenuated anxiety-like behavior in 3xTg-AD mice. We observed a correction of immunologic defects present in 3xTg-AD mice (−22% CD4/CD8 blood ratio; −17% IL-5/IL-10 ratio in the cortex) and a modulation of CX3CR1⁺ cell population (−13% in the bone marrow). IVIg treatment led to limited effects on tau pathology but resulted in a 22% reduction of the soluble Aβ42/Aβ40 ratio and a 60% decrease in concentrations of 56 kDa Aβ oligomers (Aβ*56).

Conclusion

The memory-enhancing effect of IVIg reported here suggests that Aβ oligomers, effector T cells and the fractalkine pathway are potential pharmacological targets of IVIg in AD.

Chronic airway-induced allergy in mice modifies gene expression in the brain toward insulin resistance and inflammatory responses

BACKGROUND

Chronic systemic inflammation affects brain functionality and may negatively influence the progression of neurodegenerative disorders. Allergy is a chronic inflammatory disease affecting more than 20% of the Western population. Little is known regarding the influence of allergy on brain functions. The aim of the present study was to obtain a global overview of the genes that drive the effects of peripheral inflammation associated with chronic airway-induced allergy in the brain.

METHODS

Airway allergy was induced in C57B/6J mice using ovalbumin as the allergen. Microarray analysis was performed in the hippocampus and frontal cortex in association with Affymetrix. For the data analysis, principal component analysis and orthogonal to latent structures discriminant analysis followed by pathway analysis were used. Quantitative polymerase chain reaction (qPCR) and protein analysis by Western blotting were performed for the validation of microarray results.

RESULTS

Microarray analysis showed low-grade changes in gene expression in the brain induced by airway-associated allergy. Changes in expression were observed for genes involved in antigen processing and presentation, cytokine-cytokine interaction, Toll-like receptor and mitogen-activated protein kinase signaling, as determined by pathway analysis. We confirmed a reduction of insulin-degrading enzyme at the protein level and a decrease in insulin receptor phosphorylation in the brains of allergic mice. Other allergy-induced gene expression changes were confirmed by qPCR, including increased levels of tumor necrosis factor receptor superfamily member 23 and lipopolysaccharide-binding protein.

CONCLUSION

Airway-associated allergy induces changes in brain gene expression toward induction of insulin resistance and inflammatory responses with potential implications for neurodegenerative disorders.

Allergy influences the inflammatory status of the brain and enhances tau-phosphorylation

Despite the existing knowledge regarding the neuropathology of Alzheimer's disease (AD), the cause of sporadic forms of the disease is unknown. It has been suggested that systemic inflammation may have a role, but the exact mechanisms through which inflammatory processes influence the pathogenesis and progress of AD are not obvious. Allergy is a chronic inflammatory disease affecting more than 20% of the Western population, but the effects of allergic conditions on brain functions are largely unknown. The aim of this study was to investigate whether or not chronic peripheral inflammation associated with allergy affects the expression of AD-related proteins and inflammatory markers in the brain. On the basis of previously described models for allergy in mice we developed a model of chronic airway allergy in mouse, with ovalbumin as allergen. The validity of the chronic allergy model was confirmed by a consistent and reproducible eosinophilia in the bronchoalveolar lavage (BAL) fluid of allergic animals. Allergic mice were shown to have increased brain levels of both immunoglobulin (Ig) G and IgE with a widespread distribution. Allergy was also found to increase phosphorylation of tau protein in the brain. The present data support the notion that allergy-dependent chronic peripheral inflammation modifies the brain inflammatory status, and influences phosphorylation of an AD-related protein, indicating that allergy may be yet another factor to be considered for the development and/or progression of neurodegenerative diseases such as AD.

A Critical Review of the Use of Telephone Tests to Identify Cognitive Impairment in Epidemiology and Clinical Research

We reviewed the use of telephone tests to identify cognitive impairment. We searched PubMed for epidemiological studies and clinical trials reporting the use of telephone tests to identify cognitive impairment. Validation studies and papers published more than 10 years ago were excluded. A total of 132 abstracts were identified, from which 19 epidemiological studies and four clinical trials were selected. Telephone tests were found to reduce selection bias in epidemiology by including people over large areas and facilitating follow-up in longitudinal studies. The most widely used tests were the Telephone Interview for Cognitive Status (TICS) and its modified version, the TICSm. Interviewing a proxy was included in most of the studies to compensate for the unavailability of some participants because of deafness, disease or death. In the epidemiological studies, results of telephone tests were seldom confirmed by a medical examination. Telephone screening for cognitive impairment to identify individuals eligible for clinical trials is impeded by low efficiency and lack of sensitivity for separating early pathological cognitive impairment from dementia and normal ageing.

The membrane-spanning 4-domains, subfamily A (MS4A) gene cluster contains a common variant associated with Alzheimer's disease

Background

In order to identify novel loci associated with Alzheimer's disease (AD), we conducted a genome-wide association study (GWAS) in the Spanish population.

Methods

We genotyped 1,128 individuals using the Affymetrix Nsp I 250K chip. A sample of 327 sporadic AD patients and 801 controls with unknown cognitive status from the Spanish general population were included in our initial study. To increase the power of the study, we combined our results with those of four other public GWAS datasets by applying identical quality control filters and the same imputation methods, which were then analyzed with a global meta-GWAS. A replication sample with 2,200 sporadic AD patients and 2,301 controls was genotyped to confirm our GWAS findings.

Results

Meta-analysis of our data and independent replication datasets allowed us to confirm a novel genome-wide significant association of AD with the membrane-spanning 4-domains subfamily A (MS4A) gene cluster (rs1562990, P = 4.40E-11, odds ratio = 0.88, 95% confidence interval 0.85 to 0.91, n = 10,181 cases and 14,341 controls).

Conclusions

Our results underscore the importance of international efforts combining GWAS datasets to isolate genetic loci for complex diseases.

Designing prevention programmes to reduce incidence of dementia: prospective cohort study of modifiable risk factors

OBJECTIVE

To estimate the percentage reduction in incidence of dementia that would be obtained if specific risk factors were eliminated.

DESIGN

Prospective seven year cohort study.

SETTING

General population, Montpellier, France.

PARTICIPANTS

1433 people aged over 65 with a mean baseline age of 72.5 (SD 5.1) years.

MAIN OUTCOME MEASURES

Diagnosis of mild cognitive impairment or dementia established by a standardised neurological examination.

RESULTS

Cox models were constructed to derive hazard ratios and determine confounding and interaction effects for potentially modifiable risk factors for dementia. Mean percentage population attributable fractions were calculated with 95% confidence intervals derived from bootstrapping for seven year incidence of mild cognitive impairment or dementia. The final model retained crystallised intelligence (population attributable fraction 18.11%, 95% confidence interval 10.91% to 25.42%), depression (10.31%, 3.66% to 17.17%), fruit and vegetable consumption (6.46%, 0.15% to 13.06%), diabetes (4.88%, 1.87% to 7.98%), and apolipoprotein E epsilon4 allele (7.11%, 2.44% to 11.98%).

CONCLUSIONS

Increasing crystallised intelligence and fruit and vegetable consumption and eliminating depression and diabetes are likely to have the biggest impact on reducing the incidence of dementia, outweighing even the effect of removing the principal known genetic risk factor. Although causal relations cannot be concluded with certainty, the study suggests priorities that may inform public health programmes.

Nonstroke cardiovascular disease and risk of Alzheimer disease and dementia

Unresolved issues in dementia research include (1) the association between nonstroke cardiovascular disease (CVD) and Alzheimer disease (AD) and (2) whether the association between CVD and dementia is mediated by familial factors (ie, genes and early life environment). We therefore conducted a study with both a longitudinal and a co-twin control design in 2214 Swedish twins with clinical dementia evaluation and apolipoprotein E (ApoE) genotyping. The analyses were then replicated in a register-based cohort of 18,405 individuals. Results show that CVD increases the risk of AD in carriers (but not noncarriers) of the ApoE4 allele (hazard ratio 2.39, 95% confidence interval 1.15-4.96). CVD was also associated with an almost 2-fold increased risk of developing late-life dementia (hazard ratio 1.83, 95% confidence interval 1.23-2.72). Within twin pairs, the dementia-affected twin was more likely to have had CVD than the nondemented twin partner (odds ratio 1.86, 95% confidence interval 1.11-3.13). In conclusion, this study shows that (1) nonstroke CVD increases the risk of late-life dementia but that it is only a risk factor for AD in carriers of the ApoE4 allele and (2) the association between CVD and dementia is not explained by genetic or early life environmental factors in common to both disorders.

Association between mid-life marital status and cognitive function in later life: population based cohort study

OBJECTIVES

To evaluate whether mid-life marital status is related to cognitive function in later life.

DESIGN

Prospective population based study with an average follow-up of 21 years.

SETTING

Kuopio and Joensuu regions in eastern Finland.

PARTICIPANTS

Participants were derived from random, population based samples previously investigated in 1972, 1977, 1982, or 1987; 1449 individuals (73%), aged 65-79, underwent re-examination in 1998.

MAIN OUTCOME MEASURES

Alzheimer's disease and mild cognitive impairment.

RESULTS

People cohabiting with a partner in mid-life (mean age 50.4) were less likely than all other categories (single, separated, or widowed) to show cognitive impairment later in life at ages 65-79. Those widowed or divorced in mid-life and still so at follow-up had three times the risk compared with married or cohabiting people. Those widowed both at mid-life and later life had an odds ratio of 7.67 (1.6 to 40.0) for Alzheimer's disease compared with married or cohabiting people. The highest increased risk for Alzheimer's disease was in carriers of the apolipoprotein E e4 allele who lost their partner before mid-life and were still widowed or divorced at follow-up. The progressive entering of several adjustment variables from mid-life did not alter these associations.

CONCLUSIONS

Living in a relationship with a partner might imply cognitive and social challenges that have a protective effect against cognitive impairment later in life, consistent with the brain reserve hypothesis. The specific increased risk for widowed and divorced people compared with single people indicates that other factors are needed to explain parts of the results. A sociogenetic disease model might explain the dramatic increase in risk of Alzheimer's disease for widowed apolipoprotein E e4 carriers.