Baseline serum cholesterol is selectively associated with motor speed and not rates of cognitive decline: the Women's Health and Aging Study II

Roles of peripheral lipoproteins and cholesteryl ester transfer protein in the vascular contributions to cognitive impairment and dementia

This narrative review focuses on the role of cholesteryl ester transfer protein (CETP) and peripheral lipoproteins in the vascular contributions to cognitive impairment and dementia (VCID). Humans have a peripheral lipoprotein profile where low-density lipoproteins (LDL) represent the dominant lipoprotein fraction and high-density lipoproteins (HDL) represent a minor lipoprotein fraction. Elevated LDL-cholesterol (LDL-C) levels are well-established to cause cardiovascular disease and several LDL-C-lowering therapies are clinically available to manage this vascular risk factor. The efficacy of LDL-C-lowering therapies to reduce risk of all-cause dementia and AD is now important to address as recent studies demonstrate a role for LDL in Alzheimer's Disease (AD) as well as in all-cause dementia. The LDL:HDL ratio in humans is set mainly by CETP activity, which exchanges cholesteryl esters for triglycerides across lipoprotein fractions to raise LDL and lower HDL as CETP activity increases. Genetic and pharmacological studies support the hypothesis that CETP inhibition reduces cardiovascular risk by lowering LDL, which, by extension, may also lower VCID. Unlike humans, wild-type mice do not express catalytically active CETP and have HDL as their major lipoprotein fraction. As HDL has potent beneficial effects on endothelial cells, the naturally high HDL levels in mice protect them from vascular disorders, likely including VCID. Genetic restoration of CETP expression in mice to generate a more human-like lipid profile may increase the relevance of murine models for VCID studies. The therapeutic potential of existing and emerging LDL-lowering therapies for VCID will be discussed. Figure Legend. Cholesteryl Ester Transfer Protein in Alzheimer's Disease. CETP is mainly produced by the liver, and exchanges cholesteryl esters for triglycerides across lipoprotein fractions to raise circulating LDL and lower HDL as CETP activity increases. Low CETP activity is associated with better cardiovascular health, due to decreased LDL and increased HDL, which may also improve brain health. Although most peripheral lipoproteins cannot enter the brain parenchyma due to the BBB, it is increasingly appreciated that direct access to the vascular endothelium may enable peripheral lipoproteins to have indirect effects on brain health. Thus, lipoproteins may affect the cerebrovasculature from both sides of the BBB. Recent studies show an association between elevated plasma LDL, a well-known cardiovascular risk factor, and a higher risk of AD, and considerable evidence suggests that high HDL levels are associated with reduced CAA and lower neuroinflammation. Considering the potential detrimental role of LDL in AD and the importance of HDL's beneficial effects on endothelial cells, high CETP activity may lead to compromised BBB integrity, increased CAA deposits and greater neuroinflammation. Abbreviations: CETP - cholesteryl transfer ester protein; LDL - low-density lipoproteins; HDL - high-density lipoproteins; BBB - blood-brain barrier; CAA - cerebral amyloid angiopathy, SMC - smooth muscle cells, PVM - perivascular macrophages, RBC - red blood cells.

Midlife lipid and glucose levels are associated with Alzheimer's disease

INTRODUCTION

It is unknown whether vascular and metabolic diseases assessed in early adulthood are associated with Alzheimer's disease (AD) later in life.

METHODS

Association of AD with lipid fractions, glucose, blood pressure, body mass index (BMI), and smoking obtained prospectively from 4932 Framingham Heart Study (FHS) participants across nine quadrennial examinations was evaluated using Cox proportional hazard and Kaplan-Meier models. Age-, sex-, and education-adjusted models were tested for each factor measured at each exam and within three adult age groups (early = 35-50, middle = 51-60, and late = 61-70).

RESULTS

A 15 mg/dL increase in high density lipoprotein (HDL) cholesterol was associated with decreased AD risk during early (15.4%, P = 0.041) and middle (17.9%, P = 0.014) adulthood. A 15 mg/dL increase in glucose measured during middle adulthood was associated with 14.5% increased AD risk (P = 0.00029). These findings remained significant after adjusting for treatment.

DISCUSSION

Our findings suggest that careful management of cholesterol and glucose beginning in early adulthood can lower AD risk.

The Triglyceride-Glucose Index Is Associated with Longitudinal Cognitive Decline in a Middle-Aged to Elderly Population: A Cohort Study

BACKGROUND

To examine the effect of the triglyceride-glucose (TyG) index on longitudinal cognitive decline in a healthy middle-aged-to-elderly population.

METHODS

We conducted a population-based longitudinal study. A total of 1774 participants without cognitive impairment were enrolled in the 4-year follow-up. They were divided into four groups according to the quartile of the TyG index. Multivariable-adjusted Cox proportional hazard models were performed to examine the association between the TyG index and cognitive decline. Discrimination tests were used to evaluate the incremental predictive value of the TyG index beyond conventional risk factors.

RESULTS

During the follow-up, compared with those in the bottom quartile group, participants in the top TyG quartile group presented a 51% increase in the risk of cognitive decline (OR 1.51 (95% CI: 1.06-2.14)). As shown by discrimination tests, adding the TyG index into the conventional model resulted in a slight improvement in predicting the risk of cognitive decline (NRI 16.00% (p = 0.004)).

CONCLUSION

This study demonstrated that increasing values of the TyG index were positively associated with the risk of cognitive decline. Monitoring the TyG index may help in the early identification of individuals at high risk of cognitive deterioration.

The Associations of Dietary Copper With Cognitive Outcomes

Dietary copper intake may be associated with cognitive decline and dementia. We used data from 10,269 participants of the Atherosclerosis Risks in Communities Study to study the associations of dietary copper intake with 20-year cognitive decline and incident dementia. Dietary copper intake from food and supplements was quantified using food frequency questionnaires. Cognition was assessed using 3 cognitive tests at study visits; dementia was ascertained at study visits and via surveillance. Multiple imputation by chained equations was applied to account for the missing information of cognitive function during follow-up. Survival analysis with parametric models and mixed-effect models were used to estimate the associations for incident dementia and cognitive decline, respectively. During 20 years of follow-up (1996-1998 to 2016-2017), 1,862 incident cases of dementia occurred. Higher intake of dietary copper from food was associated with higher risk of incident dementia among those with high intake of saturated fat (hazard ratio = 1.49, 95% confidence interval: 1.04, 1.95). Higher intake of dietary copper from food was associated with greater decline in language overall (beta = -0.12, 95% confidence interval: -0.23, -0.02). Therefore, a diet high in copper, particularly when combined with a diet high in saturated fat, may increase the risk of cognitive impairment.

Metabolites Associated with Memory and Gait: A Systematic Review

We recently found that dual decline in memory and gait speed was consistently associated with an increased risk of dementia compared to decline in memory or gait only or no decline across six aging cohorts. The mechanisms underlying this relationship are unknown. We hypothesize that individuals who experience dual decline may have specific pathophysiological pathways to dementia which can be indicated by specific metabolomic signatures. Here, we summarize blood-based metabolites that are associated with memory and gait from existing literature and discuss their relevant pathways. A total of 39 eligible studies were included in this systematic review. Metabolites that were associated with memory and gait belonged to five shared classes: sphingolipids, fatty acids, phosphatidylcholines, amino acids, and biogenic amines. The sphingolipid metabolism pathway was found to be enriched in both memory and gait impairments. Existing data may suggest that metabolites from sphingolipids and the sphingolipid metabolism pathway are important for both memory and gait impairments. Future studies using empirical data across multiple cohorts are warranted to identify metabolomic signatures of dual decline in memory and gait and to further understand its relationship with future dementia risk.

Association between lipoprotein cholesterol and future cardiovascular disease and mortality in older adults: a Korean nationwide longitudinal study

BACKGROUND

Dyslipidemia is considered an independent health risk factor of cardiovascular disease (CVD), a leading cause of mortality in older adults. Despite its importance, there have been few reports on the association between lipoprotein cholesterol and future CVD and cardiovascular (CV) mortality among elderly Asians aged ≥ 65 years. This study investigated the association between lipoprotein cholesterol and future CVD and CV mortality in an elderly Korean population using a large nationwide sample.

METHODS

From the cohort database of the Korean National Health Insurance Service, 62,604 adults aged ≥ 65 years (32,584 men and 30,020 women) were included. High-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C) levels were categorized by quartiles. Cox proportional hazard models and linear regression analyses were used to assess the association between the quartiles of lipoprotein cholesterol and future CV events or mortality.

RESULTS

The mean follow-up period was 3.3 years. The incidence rates of ischemic heart disease and ischemic brain disease were 0.97 and 0.61 per 1,000 person-years, respectively, and the mortality rates from these diseases were 0.22 and 0.34 per 1,000 person-years, respectively. In a completely adjusted model, high HDL-C and LDL-C levels were not associated with total CV events and CVD mortality. However, high LDL-C levels were significantly associated with a lower incidence of ischemic brain disease. Furthermore, diabetic patients with high LDL-C levels were more likely to have higher CV mortality, whereas non-smokers with high LDL-C levels were less likely to be at risk of CV events.

CONCLUSIONS

Neither high LDL-C nor HDL-C levels were significantly associated with future CV mortality in older adults aged ≥ 65 years. High LDL-C levels do not seem to be a risk factor for CVD in elderly individuals, and further studies are required.

Sex-specific associations between lipids and cognitive decline in the middle-aged and elderly: a cohort study of Chinese adults

Background

Studies regarding the lipid-cognition relationship have increasingly gained popularity but have generated much mixed results. To date, few studies have focused on the difference between sexes.

Methods

This study included 6792 Chinese adults aged over 45 years (women, 48.56%; mean age, 57.28 years), who were free of severe conditions known to affect cognitive function at the baseline (2011). Blood concentrations of total cholesterol (TC), high-density lipoprotein cholesterol (HDL-c), low-density lipoprotein cholesterol (LDL-c), and triglycerides (TG) were assessed at baseline, and both continuous and categorical values were used in final analyses. Global cognitive functions were assessed by the word recall test and the mental status test in 2011, 2013, and 2015, respectively. We graded participants into three groups according to the cognitive change slopes: no decline (≥ 0), moderate decline (median to 0), and severe decline (< median). Sex-specific associations between blood lipids and cognitive decline were analyzed using ordinal logistic models, adjusting for sociodemographic information, lifestyle behaviors, and health status.

Results

Higher baseline TC and LDL-C concentrations exhibited no significant association with 5-year cognitive decline in men but were significantly associated with greater 5-year cognitive decline in women [odds ratio (OR) 1.026, 95% confidence interval (CI) 1.003, 1.050; OR 1.026, CI 1.002, 1.051, respectively]. For higher serum HDL-c levels, a significantly protective effect on cognition was observed in men, but a slightly adverse effect was found in women (not significant after Bonferroni correction). TG presented almost no effect on later cognition in either sex.

Conclusion

Different associations between sexes were observed for the lipid-cognition relationship, and maintaining serum cholesterol levels at an appropriate range may have a positive effect on cognitive health.

Evidence from two cohorts for the frailty syndrome as an emergent state of parallel dysregulation in multiple physiological systems

Frailty is a clinical syndrome often present in older adults and characterized by a heightened vulnerability to stressors. The biological antecedents and etiology of frailty are unclear despite decades of research: frailty is associated with dysregulation in a wide range of physiological systems, but no specific cause has been identified. Here, we test predictions stemming from the hypothesis that there is no specific cause: that frailty is an emergent property arising from the complex systems dynamics of the broad loss of organismal homeostasis. Specifically, we use dysregulation of six physiological systems using the Mahalanobis distance approach in two cohorts of older adults to test the breadth, diffuseness, and nonlinearity of associations between frailty and system-specific dysregulation. We find clear support for the breadth of associations between frailty and physiological dysregulation: positive associations of all systems with frailty in at least some analyses. We find partial support for diffuseness: the number of systems or total amount of dysregulation is more important than the identity of the systems dysregulated, but results only partially replicate across cohorts. We find partial support for nonlinearity: trends are exponential but not always significantly so, and power is limited for groups with very high levels of dysregulation. Overall, results are consistent with-but not definitive proof of-frailty as an emergent property of complex systems dynamics. Substantial work remains to understand how frailty relates to underlying physiological dynamics across systems.

Associations between Serum Levels of Cholesterol and Survival to Age 90 in Postmenopausal Women

OBJECTIVES

Although elevated lipid levels predict increased risk of coronary heart disease and death in middle-aged women and men, evidence is mixed if lipid levels measured in later life predict survival to very old ages. We examined lipid levels and survival to age 90 with or without intact mobility in a large cohort of older women.

DESIGN

Prospective cohort.

SETTING

Laboratory collection at a Women's Health Initiative (WHI) center and longitudinal follow-up via mail.

PARTICIPANTS

Women aged 68 to 81 years at baseline.

MEASUREMENTS

Serum high-density lipoprotein (HDL) and low-density lipoprotein (LDL) cholesterol were collected at baseline. Participant survival status and self-reported mobility was compared across lipid levels.

RESULTS

HDL and LDL levels were not associated with survival to age 90 after adjustment for cardiovascular risk factors (HDL: quartile (Q) 2: odds ratio [OR] = 1.14 [95% confidence interval [CI] = .94-1.38]; Q3 OR = 1.08 [95% CI = .88-1.33]; Q4 OR = 1.09 [95% CI = .88-1.35]; LDL: Q2 OR = 1.07 [95% CI = .88-1.31]; Q3 OR = 1.27 [95% CI = 1.04-1.55]; Q4 OR = 1.07 [95% CI = .88-1.31]). Similarly, no associations were observed between HDL and LDL levels and survival to age 90 with mobility disability. High HDL was not associated with survival to age 90 with intact mobility after adjustment for other cardiovascular risk factors. Compared with the lowest LDL quartile, the three upper LDL quartiles were associated with greater odds of survival to age 90 with intact mobility (LDL: Q2 OR = 1.31 [95% CI = .99-1.74]; Q3 OR = 1.43 [95% CI = 1.07-1.92]; Q4 OR = 1.35 [95% CI = 1.01-1.80]; P = .05).

CONCLUSION

Neither higher HDL nor lower LDL levels predicted survival to age 90, but higher LDL predicted healthy survival. These findings suggest the need for reevaluation of healthy LDL levels in older women. J Am Geriatr Soc 68:288-296, 2020.

A systematic review of existing peripheral biomarkers of cognitive aging: Is there enough evidence for biomarker proxies in behavioral modification interventions?: An initiative in association with the nutrition, exercise and lifestyle team of the Canadian Consortium on Neurodegeneration in Aging

Peripheral biomarkers have shown significant value in predicting brain health and may serve as a useful proxy measurement in the assessment of evidence-based lifestyle behavior modification programs, including physical activity and nutrition programs, that aim to maintain cognitive function in late life. The aim of this systematic review was to elucidate which peripheral biomarkers are robustly associated with cognitive function among relatively healthy non-demented older adults. Following the standards for systematic reviews (PICO, PRIMSA), and employing MEDLINE and Scopus search engines, 222 articles were included in the review. Based on the review of biomarker proxies of cognitive health, it is recommended that a comprehensive biomarker panel, or biomarker signature, be developed as a clinical end point for behavior modification trials aimed at enhancing cognitive function in late life. The biomarker signature should take a multisystemic approach, including lipid, immune/inflammatory, and metabolic biomarkers in the biological signature index of cognitive health.

Integrating Frailty and Cognitive Phenotypes: Why, How, Now What?

PURPOSE OF REVIEW

This review elucidates the concept of frailty in relationship to reserve and resilience, the relationships and shared pathophysiology between physical frailty and cognitive impairment, the theoretical underpinnings of three integrated phenotypes of physical and cognitive impairments, and the potential of incorporating biomarkers into phenotype refinement and validation.

RECENT FINDINGS

The fact that frailty and cognitive impairment are associated and often coexist in older adults has led to the popular view of expanding the definition of frailty to include cognitive impairment. However, there is great variability in approaches to and assumptions regarding the integrated phenotypes of physical frailty and cognitive impairment.

SUMMARY

The development of integrated frailty and cognitive phenotypes should explicate the types of frailty and cognitive impairment they intend to capture and prioritize the incorporation of biological theories that help determine shared and distinct pathways in the progression to physical and cognitive impairments.

HDL from an Alzheimer's disease perspective

PURPOSE OF REVIEW

We review current knowledge regarding HDL and Alzheimer's disease, focusing on HDL's vasoprotective functions and potential as a biomarker and therapeutic target for the vascular contributions of Alzheimer's disease.

RECENT FINDINGS

Many epidemiological studies have observed that circulating HDL levels associate with decreased Alzheimer's disease risk. However, it is now understood that the functions of HDL may be more informative than levels of HDL cholesterol (HDL-C). Animal model studies demonstrate that HDL protects against memory deficits, neuroinflammation, and cerebral amyloid angiopathy (CAA). In-vitro studies using state-of-the-art 3D models of the human blood-brain barrier (BBB) confirm that HDL reduces vascular Aβ accumulation and attenuates Aβ-induced endothelial inflammation. Although HDL-based therapeutics have not been tested in clinical trials for Alzheimer's disease , several HDL formulations are in advanced phase clinical trials for coronary artery disease and atherosclerosis and could be leveraged toward Alzheimer's disease .

SUMMARY

Evidence from human studies, animal models, and bioengineered arteries supports the hypothesis that HDL protects against cerebrovascular dysfunction in Alzheimer's disease. Assays of HDL functions relevant to Alzheimer's disease may be desirable biomarkers of cerebrovascular health. HDL-based therapeutics may also be of interest for Alzheimer's disease, using stand-alone or combination therapy approaches.

ApoA-I deficiency increases cortical amyloid deposition, cerebral amyloid angiopathy, cortical and hippocampal astrogliosis, and amyloid-associated astrocyte reactivity in APP/PS1 mice

Background

Alzheimer’s disease (AD) is defined by amyloid beta (Aβ) plaques and neurofibrillary tangles and characterized by neurodegeneration and memory loss. The majority of AD patients also have Aβ deposition in cerebral vessels known as cerebral amyloid angiopathy (CAA), microhemorrhages, and vascular co-morbidities, suggesting that cerebrovascular dysfunction contributes to AD etiology. Promoting cerebrovascular resilience may therefore be a promising therapeutic or preventative strategy for AD. Plasma high-density lipoproteins (HDL) have several vasoprotective functions and are associated with reduced AD risk in some epidemiological studies and with reduced Aβ deposition and Aβ-induced inflammation in 3D engineered human cerebral vessels. In mice, deficiency of apoA-I, the primary protein component of HDL, increases CAA and cognitive dysfunction, whereas overexpression of apoA-I from its native promoter in liver and intestine has the opposite effect and lessens neuroinflammation. Similarly, acute peripheral administration of HDL reduces soluble Aβ pools in the brain and some studies have observed reduced CAA as well. Here, we expand upon the known effects of plasma HDL in mouse models and in vitro 3D artery models to investigate the interaction of amyloid, astrocytes, and HDL on the cerebrovasculature in APP/PS1 mice.

Methods

APP/PS1 mice deficient or hemizygous for Apoa1 were aged to 12 months. Plasma lipids, amyloid plaque deposition, Aβ protein levels, protein and mRNA markers of neuroinflammation, and astrogliosis were assessed using ELISA, qRT-PCR, and immunofluorescence. Contextual and cued fear conditioning were used to assess behavior.

Results

In APP/PS1 mice, complete apoA-I deficiency increased total and vascular Aβ deposition in the cortex but not the hippocampus compared to APP/PS1 littermate controls hemizygous for apoA-I. Markers of both general and vascular neuroinflammation, including Il1b mRNA, ICAM-1 protein, PDGFRβ protein, and GFAP protein, were elevated in apoA-I-deficient APP/PS1 mice. Additionally, apoA-I-deficient APP/PS1 mice had elevated levels of vascular-associated ICAM-1 in the cortex and hippocampus and vascular-associated GFAP in the cortex. A striking observation was that astrocytes associated with cerebral vessels laden with Aβ or associated with Aβ plaques showed increased reactivity in APP/PS1 mice lacking apoA-I. No behavioral changes were observed.

Conclusions

ApoA-I-containing HDL can reduce amyloid pathology and astrocyte reactivity to parenchymal and vascular amyloid in APP/PS1 mice.

Electronic supplementary material

The online version of this article (10.1186/s13195-019-0497-9) contains supplementary material, which is available to authorized users.

Increases in total cholesterol and low density lipoprotein associated with decreased cognitive performance in healthy elderly adults

The current study examined associations between blood lipid profiles and cognitive functioning using a healthy non-demented elderly sample. The sample comprised 196 healthy volunteers (male; 86: female 110) aged 60-75 years from the Australian Research Council Longevity Intervention (ARCLI) study cohort. Serum total cholesterol (T-C), low density lipoprotein cholesterol (LDL-c), high density lipoprotein cholesterol (HDL-c) and triglycerides (TGL) were collected, and participants completed the Swinburne University Computerized Cognitive Assessment Battery (SUCCAB). In line with prediction, higher levels of T-C and LDL-c were found to be associated with impaired speeds of response in tasks assessing recognition memory, working memory and inhibitory processing. However, contrary to prediction both TGL and HDL-c were found to be unrelated to cognitive functioning in the current sample. It is suggested that frontal lobe function may be differentially sensitive to the effects of T-C and LDL-c accumulation during the aging process. Future data collection as part of the larger ARCLI intervention study will provide important follow-up data regarding the ability of the baseline blood lipid data to predict subsequent cognitive change.

Associations of dyslipidaemia and lipid-lowering treatment with risk of postoperative cognitive dysfunction: a systematic review and meta-analysis

BACKGROUND

Lipid imbalance is linked to age-related cognitive impairment, but its role in postoperative cognitive dysfunction (POCD) is unknown. Here, we present a systematic review and meta-analysis on dyslipidaemia, lipid-lowering treatment and POCD risk.

METHODS

PubMed, Ovid SP and Cochrane databases were searched for longitudinal studies that reported on associations of any measure of dyslipidaemia and/or lipid-lowering treatment with POCD as relative risks (RRs) or ORs. Fixed-effects inverse variance models were used to combine effects.

RESULTS

Of 205 articles identified in the search, 17 studies on 2725 patients (grand mean age 67 years; mean age range 61-71 years) with follow-up periods of 1 day to 4 years (median 7 days; IQR 1-68 days) were included. Studies focused almost exclusively on hypercholesterolaemia as a measure of dyslipidaemia and on statins as lipid-lowering treatment. Across 12 studies on hypercholesterolaemia, we found no association with POCD risk (RR 0.93; 95% CI 0.80 to 1.08; P=0.34). Statin use before surgery was associated with a reduced POCD risk across eight studies (RR 0.81; 95% CI 0.67 to 0.98; P=0.03), but data on treatment duration were lacking.

CONCLUSION

Statin users appear to be at reduced risk of POCD although hypercholesterolaemia per se may not be associated with POCD risk. Trial studies are needed to evaluate the usefulness of statins in POCD prevention.

The association of total cholesterol with processing speed is moderated by age in mid- to late-age healthy adults

OBJECTIVES

To investigate the nature of the association of normal levels of total cholesterol with cognitive function and the contribution of age to this association.

METHODS

A sample of 61 senior executives, who were summoned for an annual medical examination with approximately four measurements of total cholesterol during 4 years, were examined with a computerized cognitive battery assessing mental processing speed as a sensitive measure of cognitive decline. We examined the association of total cholesterol with processing speed and the moderating effect of age on this association.

RESULTS

A multiple regression analysis yielded a significant interaction between cholesterol and age for processing speed (p = .045). In order to examine the source of the interaction, simple slope analysis was performed. A significant negative high correlation was found for young subjects (p = .021), while no significant correlation was observed at middle (p = .286) or older (p = .584) age. The difference in slopes was robust to adjustment for potential confounding factors, including body mass index, and fasting glucose.

CONCLUSIONS

Within the normal range, higher total cholesterol levels were associated with better processing speed in younger ages and this association diminished with increasing age. Our findings highlight the important role of brain cholesterol in good cognitive functioning.

Sex-specific nonlinear associations between serum lipids and different domains of cognitive function in middle to older age individuals

To examine how serum lipids relates to specific cognitive ability domains between the men and women in Chinese middle to older age individuals. A complete lipid panel was obtained from 1444 individuals, ages 50-65, who also underwent a selection of cognitive tests. Participants were 584 men and 860 women from Linyi city, Shandong province. Multiple linear regression analyses examined serum lipids level as quadratic predictors of sex-specific measure of performance in different cognitive domains, which were adjusted for sociodemographic and lifestyle characteristics. In men, a significant quadratic effect of total cholesterol (TC) was identified for Digit Symbol (B = -0.081, P = 0.044) and also quadratic effect of low density lipoprotein-cholesterol (LDL-C) was identified for Trail Making Test B (B = -0.082, P = 0.045). Differently in women, there were significant quadratic associations between high density lipoprotein-cholesterol (HDL-C) and multiple neuropsychological tests. The nonlinear lipid-cognition associations differed between men and women and were specific to certain cognitive domains and might be of potential relevance for prevention and therapy of cognitive decline.

Updating the Evidence on the Association between Serum Cholesterol and Risk of Late-Life Dementia: Review and Meta-Analysis

BACKGROUND

Cohort studies have reported that midlife high total serum cholesterol (TC) is associated with increased risk of Alzheimer's disease (AD) in late-life but findings have been based on few studies and previous reviews have been limited by a lack of compatible data.

OBJECTIVE

We synthesized all high quality data from cohort studies reporting on the association between total serum cholesterol measured and late-life cognitive outcomes including Alzheimer's disease (AD), vascular dementia (VaD), any dementia, mild cognitive impairment (MCI), and cognitive decline.

METHODS

The literature was searched up to October 2016 using a registered protocol. Thirty-four articles meeting study criteria were identified. Seventeen studies published from 1996 to 2014, including 23,338 participants were included in meta-analyses.

RESULTS

Relative risk of developing AD for adults with high TC in midlife was 2.14 (95% CI 1.33-3.44) compared with normal cholesterol. Individual studies that could not be pooled also reported high TC in midlife increased the risk of MCI and cognitive decline in late-life. High TC in late-life was not associated with MCI, AD, VaD, any dementia, or cognitive decline. Late-life measured HDL cholesterol and triglycerides were not associated with increased risk of VaD, and HDL was not associated with risk of MCI, AD, or any dementia. There were insufficient data to examine other cholesterol sub-fractions, sex differences, or APOE interactions.

CONCLUSIONS

Significant gaps in the literature regarding TC and late-life dementia remain. Evidence suggests that high midlife TC increases risk of late-life AD, and may correlate with the onset of AD pathology.

Cholesterol and cognitive performance among community volunteers from the Czech Republic

BACKGROUND

Research shows that lipid levels may be associated with cognitive function, particularly among women. We aimed to examine total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), triglycerides (TG), high-density lipoprotein (HDL), and HDL/LDL ratio in relation to cognitive performance, measured with six well-established cognitive domains and a composite cognitive score (CCS).

METHODS

In this cross-sectional study, biomarkers and neuropsychological assessment were available for 141 adults with MMSE scores ≥ 24 (mean age = 69 years, 47% female, mean education = 14.4 years) attending a neuropsychological evaluation. Ordinary least squares regressions were adjusted for age, gender, education, and depressive symptoms in Model 1 and also for apolipoprotein E4 (APOE4) status in Model 2.

RESULTS

High-density lipoprotein cholesterol (HDL-C) was associated with better CCS (β = 0.24; p = 0.014). This association was significant among women (β = 0.30; p = 0.026) and not among men (β = 0.20; p = 0.124). HDL-C was also related to attention/working memory (β = 0.24; p = 0.021), again only among women (β = 0.37; p = 0.012) and not men (β = 0.15; p = 0.271). Adjusting for APOE4 yielded significance for high HDL-C and CCS (β = 0.24; p = 0.022).

CONCLUSIONS

HDL-C was the main lipoprotein affecting cognitive function, with results somewhat more pronounced among women. Research should investigate the possibility of finding ways to boost HDL-C levels to potentially promote cognitive function.

Serum cholesterol and cognitive functions: the Lothian Birth Cohort 1936

BACKGROUND

We examined the associations between serum cholesterol measures, statin use, and cognitive function measured in childhood and in old age. The possibility that lifelong (trait) cognitive ability accounts for any cross-sectional associations between cholesterol and cognitive performance in older age, seen in observational studies, has not been tested to date.

METHODS

Participants were 1,043 men and women from the Lothian Birth Cohort 1936 Study, most of whom had participated in a nationwide IQ-type test in childhood (Scottish Mental Survey of 1947), and were followed up at about age 70 years. Serum cholesterol measures included total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), triglycerides, and cholesterol:HDL cholesterol ratio. Cognitive outcome measures were age 70 IQ (using the same test as at age 11 years), general cognitive ability (g), processing speed, memory, and verbal ability.

RESULTS

Higher TC, higher HDL-C, and lower triglycerides were associated with higher age 70 cognitive scores in most cognitive domains. These relationships were no longer significant after covarying for childhood IQ, with the exception a markedly attenuated association between TC and processing speed, and triglycerides and age 70 IQ. In the fully adjusted model, all conventionally significant (p < 0.05) effects were removed. Childhood IQ predicted statin use in old age. Statin users had lower g, processing speed, and verbal ability scores at age 70 years after covarying for childhood IQ, but significance was lost after adjusting for TC levels.

CONCLUSIONS

These results suggest that serum cholesterol and cognitive function are associated in older age via the lifelong stable trait of intelligence. Potential mechanisms, including lifestyle factors, are discussed.

Interleukin-6 and C-Reactive Protein Levels and 9-Year Cognitive Decline in Community-Dwelling Older Women: The Women's Health and Aging Study II

BACKGROUND

Elevated inflammation is a proposed mechanism relating chronic diseases to cognitive dysfunction. The objective of this study was to test the hypothesis that greater levels of inflammation, as measured by the proinflammatory cytokine interleukin-6 (IL-6) and C-reactive protein, are associated with faster rates of cognitive decline among cognitively intact community-dwelling older women.

METHODS

We analyzed 336 women from the Women's Health and Aging Study II. Cognitive assessments were performed at baseline and every 18-36 months, and included the following domains: immediate and delayed memory (Hopkins Verbal Learning Test), psychomotor speed (Trail Making Test, Part A), and executive function (Trail Making Test, Part B). Aggregate measures of IL-6 and C-reactive protein, based on the average from visits one and two, were analyzed categorically. Random effects models were employed to test the relationship between tertiles of each inflammatory marker and changes in cognitive domain scores over 9 years.

RESULTS

Moderate and high levels of IL-6 predicted early declines in psychomotor speed by 1.0 connection/min per year. There were no differences in baseline scores or rates of change across tertiles of IL-6 in memory or executive function. No differences were observed across tertiles of C-reactive protein for all cognitive domains.

CONCLUSIONS

Higher levels of serum IL-6 were associated with greater declines in psychomotor speed over 9 years. This finding could suggest that elevated IL-6 may result in microvascular changes that may lead to damage of myelin sheaths that line neuronal axons, leading to decreased neuron propagation and impaired processing speed; however, mechanistic studies are needed to evaluate these hypotheses.