Could Country-Level Factors Explain Sex Differences in Dementia Incidence and Prevalence? A Systematic Review and Meta-Analysis.

BACKGROUND: Despite rising interest in sex differences in dementia, it is unclear whether sex differences in dementia incidence and prevalence are apparent globally. OBJECTIVE: We examine sex differences in incidence and prevalence of Any dementia, Alzheimer's disease (AD), and vascular dementia (VaD), and evaluate whether country-level indicators of gender inequality account for differences. METHODS: Systematic review with meta-analysis was used to obtain estimates of incidence and prevalence of Any dementia, AD, and VaD using random effects meta-analysis, and population-based studies with clinical or validated dementia measures. Meta-regression was used to evaluate how country-specific factors of life expectancy, education, and gender differences in development, unemployment, and inequality indices influenced estimates. RESULTS: We identified 205 eligible studies from 8,731 articles, representing 998,187 participants across 43 countries. There were no sex differences in the incidence of Any dementia, AD, or VaD, except in the 90+ age group (women higher). When examined by 5-year age bands, the only sex difference in prevalence of Any dementia was in the 85+ group and there was no sex difference in VaD. AD was more prevalent in women at most ages. Globally, the overall prevalence of dementia in adults 65 + was higher for women (80.22/1000, 95% CI 62.83-97.61) than men (54.86/1000, 95% CI 43.55-66.17). Meta-regression revealed that sex differences in Any dementia prevalence were associated with gender differences in life expectancy and in education. CONCLUSION: Globally, there are no sex differences in age-specific dementia incidence, but prevalence of AD is higher in women. Country-level factors like life expectancy and gender differences in education may explain variability in sex differences.

Kynurenic acid as a biochemical factor underlying the association between Western-style diet and depression: A cross-sectional study.

Consumption of a Western-style diet (WS-diet), high in saturated fat and added sugar, is associated with increased depression risk. However, the physiological mechanisms underlying the relationship requires elucidation. Diet can alter tryptophan metabolism along the kynurenine pathway (KP), potentially linking inflammation and depression. This study aimed to examine whether urinary inflammatory markers and KP metabolites differed according to WS-diet consumption and depression severity. Depression symptoms and habitual WS-diet consumption were assessed in 169 healthy adults aged 17-35 recruited from two experimental studies. Targeted metabolomics profiling of seven KP metabolites, ELISA-based assays of interleukin-6 (IL-6) and C-reactive protein (CRP) were performed using urine samples collected from the participants. Parametric tests were performed for group comparison and associations analysis. Multilevel mixed-effect modelling was applied to control for biases. Higher intake of WS-diet was associated with lower levels of neuroprotective kynurenic acid (KA; R = -0.17, p = 0.0236). There were no differences in IL-6 or CRP across diet groups (p > 0.05). Physical activity had negative associations with most KP metabolites. Mixed-effects regression analysis showed the glutamatergic inhibitor, KA, was the only biomarker to have a significant association with depression symptoms in a model adjusted for demographic and lifestyle variables: a unit increase in KA was associated with 0.21 unit decrease in Depression Anxiety and Stress Scale-21 depression score (p = 0.009). These findings suggest that urinary KA is associated with both habitual WS-diet intake, and levels of depression symptoms, independent of inflammation. Findings support the role of neuroprotection and glutamatergic modulation in depression. We propose that KA may act as endogenous glutamatergic inhibition in regulating depression severity in the absence of inflammation. Further comparison with blood-based markers will assist in validating the utility of non-invasive urine samples for measuring KP metabolites.

Gender differences in cognitive development in cohorts of young, middle, and older adulthood over 12 years.

Understanding gender differences in human cognitive development may contribute to understanding the gender differences in outcomes in cognitive ageing. However, evaluation of this topic has been hindered by a lack of representative, longitudinal data from different aged cohorts measured on the same cognitive tests. Gender differences in cognitive abilities were evaluated in three population-based cohorts (baseline age-span 20 to 76, 52% female, 94% Caucasian, 5% Asian and 1% other ethnic background, baseline N = 7,485), initially drawn from the electoral role in Australia where voting is compulsory, that were assessed four times over 12 years on measures of verbal memory, processing speed, working memory, verbal ability, and reaction time. Linear mixed models showed that within each cohort, women had better verbal memory and men had better working memory and faster reaction times. Verbal ability and processing speed showed variable gender differences in the young and middle-aged cohorts but no difference in the oldest cohort. In young and middle age, there were no gender differences in rates of change in verbal memory, processing speed, reaction time, verbal ability, or working memory. In old age, the gender differences were only observed in rates of change in verbal memory. Women showed more verbal memory decline between the 8-year and 12-year follow-ups than men, despite retaining higher average memory performance than men. We conclude that from ages 20-76, gender differences in cognitive abilities are stable except for faster memory ageing among women in the eighth decade. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

The impact of saturated fat, added sugar and their combination on human hippocampal integrity and function: A systematic review and meta-analysis.

Paralleling animal research, there is emerging evidence that a Western-style (WS) diet - high in saturated fat and added sugar - impairs human hippocampal functioning. However, the conditions under which this occurs are not fully understood and there have been published failures to detect such effects. To date, there has been no systematic review or meta-analysis of relevant human studies. We undertook a systematic database search and review. Twenty studies were identified, two experimental, with the remainder correlational. The latter were included in a meta-analyses on the impact of WS-diet and its macronutrient components on human hippocampal function. Effects of age and sex were also examined. A WS-diet adversely impacted human hippocampal volume and functioning, with a small-pooled effect size. No effects were found for individual macronutrients. There was a high-level of study heterogeneity, which was not fully explained by study/sample characteristics. This may arise via the wide range of assessment tools used to measure both dietary intake and hippocampal functioning. Overall, a WS-diet clearly impacts human hippocampal functioning as in animals.