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Fulltext Future Directions for Dementia Risk Reduction and Prevention Research: An International Research Network on Dementia Prevention Consensus

Anstey KJ, Peters R, Zheng L, Barnes DE, Brayne C, Brodaty H, et al.

J Alzheimers Dis, 2020;78(1):3-12.
PMID: 32925063 DOI: 10.3233/JAD-200674

In the past decade a large body of evidence has accumulated on risk factors for dementia, primarily from Europe and North America. Drawing on recent integrative reviews and a consensus workshop, the International Research Network on Dementia Prevention developed a consensus statement on priorities for future research. Significant gaps in geographical location, representativeness, diversity, duration, mechanisms, and research on combinations of risk factors were identified. Future research to inform dementia risk reduction should fill gaps in the evidence base, take a life-course, multi-domain approach, and inform population health approaches that improve the brain-health of whole communities.
Fulltext Exploring causality of the association between smoking and Parkinson's disease

Gallo V, Vineis P, Cancellieri M, Chiodini P, Barker RA, Brayne C, et al.

Int J Epidemiol, 2019 Jun 01;48(3):912-925.
PMID: 30462234 DOI: 10.1093/ije/dyy230

BACKGROUND: The aim of this paper is to investigate the causality of the inverse association between cigarette smoking and Parkinson's disease (PD). The main suggested alternatives include a delaying effect of smoking, reverse causality or an unmeasured confounding related to a low-risk-taking personality trait.
METHODS: A total of 715 incident PD cases were ascertained in a cohort of 220 494 individuals from NeuroEPIC4PD, a prospective European population-based cohort study including 13 centres in eight countries. Smoking habits were recorded at recruitment. We analysed smoking status, duration, and intensity and exposure to passive smoking in relation to PD onset.
RESULTS: Former smokers had a 20% decreased risk and current smokers a halved risk of developing PD compared with never smokers. Strong dose-response relationships with smoking intensity and duration were found. Hazard ratios (HRs) for smoking <20 years were 0.84 [95% confidence interval (CI) 0.67-1.07], 20-29 years 0.73 (95% CI 0.56-0.96) and >30 years 0.54 (95% CI 0.43-0.36) compared with never smokers. The proportional hazard assumption was verified, showing no change of risk over time, arguing against a delaying effect. Reverse causality was disproved by the consistency of dose-response relationships among former and current smokers. The inverse association between passive smoking and PD, HR 0.70 (95% CI 0.49-0.99) ruled out the effect of unmeasured confounding.
CONCLUSIONS: These results are highly suggestive of a true causal link between smoking and PD, although it is not clear which is the chemical compound in cigarette smoking responsible for the biological effect.
Fulltext APOE ε4 and the Influence of Sex, Age, Vascular Risk Factors, and Ethnicity on Cognitive Decline

Makkar SR, Lipnicki DM, Crawford JD, Kochan NA, Castro-Costa E, Lima-Costa MF, et al.

J Gerontol A Biol Sci Med Sci, 2020 09 25;75(10):1863-1873.
PMID: 32396611 DOI: 10.1093/gerona/glaa116

We aimed to examine the relationship between Apolipoprotein E ε4 (APOE*4) carriage on cognitive decline, and whether these associations were moderated by sex, baseline age, ethnicity, and vascular risk factors. Participants were 19,225 individuals aged 54-103 years from 15 longitudinal cohort studies with a mean follow-up duration ranging between 1.2 and 10.7 years. Two-step individual participant data meta-analysis was used to pool results of study-wise analyses predicting memory and general cognitive decline from carriage of one or two APOE*4 alleles, and moderation of these associations by age, sex, vascular risk factors, and ethnicity. Separate pooled estimates were calculated in both men and women who were younger (ie, 62 years) and older (ie, 80 years) at baseline. Results showed that APOE*4 carriage was related to faster general cognitive decline in women, and faster memory decline in men. A stronger dose-dependent effect was observed in older men, with faster general cognitive and memory decline in those carrying two versus one APOE*4 allele. Vascular risk factors were related to an increased effect of APOE*4 on memory decline in younger women, but a weaker effect of APOE*4 on general cognitive decline in older men. The relationship between APOE*4 carriage and memory decline was larger in older-aged Asians than Whites. In sum, APOE*4 is related to cognitive decline in men and women, although these effects are enhanced by age and carriage of two APOE*4 alleles in men, a higher numbers of vascular risk factors during the early stages of late adulthood in women, and Asian ethnicity.
Fulltext Estimating prevalence of subjective cognitive decline in and across international cohort studies of aging: a COSMIC study

Röhr S, Pabst A, Riedel-Heller SG, Jessen F, Turana Y, Handajani YS, et al.

Alzheimers Res Ther, 2020 12 18;12(1):167.
PMID: 33339532 DOI: 10.1186/s13195-020-00734-y

BACKGROUND: Subjective cognitive decline (SCD) is recognized as a risk stage for Alzheimer's disease (AD) and other dementias, but its prevalence is not well known. We aimed to use uniform criteria to better estimate SCD prevalence across international cohorts.
METHODS: We combined individual participant data for 16 cohorts from 15 countries (members of the COSMIC consortium) and used qualitative and quantitative (Item Response Theory/IRT) harmonization techniques to estimate SCD prevalence.
RESULTS: The sample comprised 39,387 cognitively unimpaired individuals above age 60. The prevalence of SCD across studies was around one quarter with both qualitative harmonization/QH (23.8%, 95%CI = 23.3-24.4%) and IRT (25.6%, 95%CI = 25.1-26.1%); however, prevalence estimates varied largely between studies (QH 6.1%, 95%CI = 5.1-7.0%, to 52.7%, 95%CI = 47.4-58.0%; IRT: 7.8%, 95%CI = 6.8-8.9%, to 52.7%, 95%CI = 47.4-58.0%). Across studies, SCD prevalence was higher in men than women, in lower levels of education, in Asian and Black African people compared to White people, in lower- and middle-income countries compared to high-income countries, and in studies conducted in later decades.
CONCLUSIONS: SCD is frequent in old age. Having a quarter of older individuals with SCD warrants further investigation of its significance, as a risk stage for AD and other dementias, and of ways to help individuals with SCD who seek medical advice. Moreover, a standardized instrument to measure SCD is needed to overcome the measurement variability currently dominant in the field.