Gender differences in the association between parity and cognitive function: Evidence from the UK biobank

The cognitive benefits of ecosystem improvement: Evidence from China's National Key Ecological Function Zones

Despite growing evidence of a strong correlation between ecosystem changes and human health, the direct impact of ecological improvements on cognitive function remains underexplored. This study examines the impact of China's National Key Ecological Function Zones (NKEFZs) policy on residents' cognitive function, employing a staggered Difference-in-Differences model. Using large-scale longitudinal survey data from 92,825 adults, our findings indicate that NKEFZs implementation is associated with significant improvements in cognitive outcomes, with cognitive scores increasing by 0.0291 standard deviations for vocabulary, 0.0703 for mathematical scores, and 0.0993 for overall cognitive function. Further analysis reveals that these effects are mediated by enhanced objective health status, reduced depression, and increased outdoor exercise frequency. Heterogeneity analysis suggests that the cognitive benefits of NKEFZs implementation vary across demographic groups, with older and lower-income individuals experiencing less pronounced effects. These findings emphasize the broader public health implications of ecosystem improvement.

Gender differences in the mediating effects of social participation and number of children on psychological resilience and cognitive function in older adults

The aim of this study is to explore the relationship between the number of children of older adults in China and their cognitive function. A total of 15862 older adults were included in the 2017-2018 China Health and Longevity Longitudinal Survey(CLHLS), and were explored using Structural Equation Modeling(SEM) and restricted cubic splines(RCS). Research has found that social participation and psychological resilience have a moderating effect on the impact of child numbers on cognitive function, with a greater impact observed in female participants. RCS shows a U-shaped relationship between the number of children and poorer cognitive outcomes, but low fertility rates are only associated with poorer cognitive function in women. Cognitive function decreases with decreasing social participation and psychological resilience. To combat cognitive decline in older adults with multiple children, it is imperative to take into account the societal and psychological impacts and to integrate a suite of complementary intervention strategies.

Pregnancy as a window of opportunity for dementia prevention: a narrative review

Dementia is a debilitating condition with a disproportionate impact on women. While sex differences in longevity contribute to the disparity, the role of the female sex as a biological variable in disease progression is not yet fully elucidated. Metabolic dysfunctions are drivers of dementia etiology, and cardiometabolic diseases are among the most influential modifiable risk factors. Pregnancy is a time of enhanced vulnerability for metabolic disorders. Many dementia risk factors, such as hypertension or blood glucose dysregulation, often emerge for the first time in pregnancy. While such cardiometabolic complications in pregnancy pose a risk to the health trajectory of a woman, increasing her odds of developing type 2 diabetes or chronic hypertension, it is not fully understood how this relates to her risk for dementia. Furthermore, structural and functional changes in the maternal brain have been reported during pregnancy suggesting it is a time of neuroplasticity for the mother. Therefore, pregnancy may be a window of opportunity to optimize metabolic health and support the maternal brain. Healthy dietary patterns are known to reduce the risk of cardiometabolic diseases and have been linked to dementia prevention, yet interventions targeting cognitive function in late life have largely been unsuccessful. Earlier interventions are needed to address the underlying metabolic dysfunctions and potentially reduce the risk of dementia, and pregnancy offers an ideal opportunity to intervene. This review discusses current evidence regarding maternal brain health and the potential window of opportunity in pregnancy to use diet to address neurological health disparities for women.

Number of children and dementia risk: a causal mediation analysis using data from the HUNT study linked with national registries in Norway

BACKGROUND

Childlessness, as well as having a high number of children, has been reported to be associated with an elevated risk of dementia compared to having 2-3 children. The mechanisms underlying these relationships are not well understood and may be mediated by different midlife risk factors. We examined the mediating role of various factors on the relationship between the number of children and dementia risk. These factors include socioeconomic factors (e.g., occupational complexity), psychosocial (e.g.., social activities, loneliness, life satisfaction), lifestyle (e.g., smoking, physical inactivity, alcohol intake), and chronic diseases (e.g., obesity, diabetes, depression, hearing impairment and hypertension).

METHODS

Using a historic cohort design, we included 9,745 participants born between 1931-48, with a mean age of 78.2 (SD = 6.4) years at the time of cognitive testing in the HUNT4 70 + sub-study (2017-2019). Further measures were obtained through data linkage between information from Statistics Norway and the HUNT1(1984-86), and HUNT2 (1995-97) Surveys. Causal mediation analyses using an inverse odd weighting approach were conducted to decompose the total effect of the number of children (0, 1, or 4 + children vs. 2-3) on the risk of dementia at age 70 + years into direct and indirect effects with mediators assessed at a mean age of 50.7 (SD = 6.4) years. The analyses were adjusted for age, sex, marital status at age 25 years, educational status, and religion assessed during HUNT3 (2006-2008).

RESULTS

Overall, 15.7% were diagnosed with dementia. The proportions with dementia by the number of children were 22.3% among those with no children, 21.4% for those with one child, 13% for those with 2-3 children (specifically, 12.6% for those with 2 children and 13.4% for those with 3 children), and 19.9% for those with 4 + children. Compared to the reference group of individuals with 2-3 children, the dementia risk was higher among the groups with no children (relative risk (RR): 1.30, 95% confidence interval (CI) (1.12, 1.51)), those with one child (RR: 1.30, 95% CI (1.14, 1.47)) and those with 4 + children (RR: 1.12, 95% CI (1.01, 1.24)). The elevated risks of dementia were not mediated by the socioeconomic, psychosocial, lifestyle, or chronic diseases related factors that we tested. Sex-stratified analysis showed higher dementia risk for men without children and women with one or 4 + children compared to those with 2-3 children, with similar patterns across sexes. None of the mediators contributed to mediation in either group. None of the mediators appeared to contribute through mediation in either group.

CONCLUSIONS

Our findings suggest that the number of children-specifically being childless, having one child, or having four or more children-may influence the risk of dementia. These relationships were not mediated by psychosocial, lifestyle, and socioeconomic factors, or markers of chronic diseases in adulthood considered in this study.

Childbearing Histories and Midlife Cognition: Accounting for Early Life Factors

OBJECTIVES

Childbearing histories-for example, parity and age at first birth-matter for the health outcomes of mid- and later-life women. There is growing evidence that childbearing may shape cognitive outcomes. However, previous research is not definitive due to its inability to account for selection. Selection is critical to address given that multiple factors, including socioeconomic background and cognition in adolescence, place women at risk for both specific childbearing experiences and poor cognitive functioning.

METHODS

We analyze the 1979 National Longitudinal Survey of Youth (NLSY79; N = 3,668), a longitudinal nationally representative data set from the United States that began collecting data during respondents' late teens and early 20s. We estimate the average treatment effects of childbearing histories on midlife memory and cognition using propensity-score matching techniques that incorporate an expansive set of early life factors.

RESULTS

In models adjusting for early life covariates, we find that any births, high parity, and early first birth are associated with worse self-reported memory, but not cognitive functioning scores. After addressing the influence of early life factors through matching techniques, the only robust differences relate to any births and early first births with self-reported memory.

DISCUSSION

Selection into specific childbearing experiences partially drives the link between childbearing and cognition at midlife, with cascading implications into later life. We suggest incorporating childbearing and early life factors into models to identify social determinants of memory and cognitive functioning.

Variation in Adult Cognition Across Domains and Life Course Place Effects in the UK

This study explores the role that place of birth and place of residence have in variation in cognition in adulthood in the UK. We take advantage of both the large sample size and number of cognitive domains in the UK Biobank to estimate the effect of place of birth and place of residence on adulthood cognition using multilevel modeling. We find, consistent with studies in the US, that place effects at both time points contribute modest variation (<3% of the variation) across all measured cognitive domains, suggesting a relative lack of contribution of shared environments in explaining future Alzheimer's Disease and Related Dementias. Moreover, the geographical contribution to cognitive function in adulthood was slightly larger for females than for males. This study is among the first to explore the impact of both the independent and joint associations of place of birth and place of residence with different cognitive domains.

Association between parity and female mortality: the mediative role of depressive symptoms

STUDY QUESTION

Is parity associated with all-cause and cause-specific mortality among women in a nationally representative cohort of the US population, and does depression mediate this association?

SUMMARY ANSWER

Nulliparous women have a higher risk of all-cause and cause-specific mortality, with depression partially mediating the relationship between parity and women's all-cause and cause-specific mortality.

WHAT IS KNOWN ALREADY

Parity, a significant state in reproductive life, has enduring implications for women's health. There is also a complex relationship between depression, a prevalent mental and emotional disorder, and female fertility. Previous studies have elucidated the relationships between parity and depression, both of which are associated with mortality. However, findings from studies examining parity and women's mortality have been inconsistent. Moreover, few studies have investigated whether the effect of parity on mortality is mediated by depression.

STUDY DESIGN, SIZE, DURATION

We conducted a cross-sectional study using data from seven cycles of the National Health and Nutrition Examination Survey (NHANES) spanning 2005-2018.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The study cohort comprised adult women with available parity and survival follow-up data. Parity data were self-reported and sourced from the Reproductive Health Questionnaire. Depression scores were derived from the Patient Health Questionnaire 9, and cause-specific deaths were identified using the International Statistical Classification of Diseases, 10th Revision (ICD-10). Weighted multivariable Cox regression was applied to analyze the association between parity, depression, and mortality. Weighted linear regression was performed to examine the relationship between parity and depression. Mediation analyses were employed to determine whether and to what extent depression mediated the effect of parity on mortality.

MAIN RESULTS AND THE ROLE OF CHANCE

Our study ultimately encompassed 16 962 American women. Following multivariable adjustment, compared to nulliparous women, those with one to three live births exhibited a 17% and 33% reduction in all-cause and cancer mortality, respectively (all-cause mortality: HR = 0.83, 95% CI = 0.69-0.99, P = 0.040; cancer mortality: HR = 0.67, 95% CI = 0.45-0.99, P = 0.045). Women with more than four live births demonstrated lower all-cause mortality and mortality from other (not cancer or cardiovascular disease) diseases (all-cause mortality: HR = 0.73, 95% CI = 0.58-0.93, P = 0.011; other diseases mortality: HR = 0.66, 95% CI = 0.47-0.91, P = 0.013). No correlation was detected between parity and the risk of cardiovascular disease mortality among women. Furthermore, depression was found to partially mediate the impact of parity on all-cause mortality and mortality from other diseases in women.

LIMITATIONS, REASONS FOR CAUTION

Firstly, a single index of parity was used as an exposure factor, and other reproductive factors such as birth spacing, age at first birth, and mode of delivery were not taken into account. Secondly, despite accounting for important potentially confounders in our analysis, such as BMI, smoking status, and educational level, the influence of unmeasured confounders (e.g., social class, latent reproductive system diseases) on reproductive behavior or mortality cannot be dismissed. Thirdly, women's vulnerability to depression fluctuates across reproductive stages, and the effect of depression on female fertility varies over time. Due to data constraints, we were unable to obtain information on women's mental health status at different reproductive stages. Fourthly, due to the data accessibility limitations of NHANES, we were unable to specifically explore the relationship between parity and different specific types of cancer, a limitation that may obscure potential correlations. Additionally, despite our efforts to control for various confounding factors in subgroup analyses, the smaller sample sizes in some subgroups may limit the statistical power, affecting the ability to detect effects. Finally, studies exploring the association between parity and depression are cross-sectional designs, making it difficult to infer causality. These results should be interpreted with caution, and further research is warranted to corroborate our findings.

WIDER IMPLICATIONS OF THE FINDINGS

Our study underscores the elevated risk of all-cause and cause-specific mortality in nulliparous women and reveals that depression partially mediates the negative correlation between parity and women's all-cause mortality and mortality from other diseases. These results should be interpreted with caution, and further investigation is needed to support our findings.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the National Key Research and Development Program of China (2023YFC2705700), the Key Research & Developmental Program of Hubei Province (2022BCA042), and the Interdisciplinary Innovative Talents Foundation from Renmin Hospital of Wuhan University (JCRCWL-2022-001). The authors declare that they have no conflict of interest.

TRIAL REGISTRATION NUMBER

N/A.

Higher Number of Children Is Associated With Increased Risk of Generalization Deficits in Older African American Women

OBJECTIVES

The objectives of this project were to: (1) examine the relationship between the number of biological children and hippocampal-dependent cognitive performance among older African American women and (2) determine the influence of socioeconomic status (i.e., age, education, marital status, median household income), if any, on this relationship.

METHODS

A total of 146 cognitively unimpaired African American women aged 60 and older were recruited from the greater Newark area and reported their number of biological children, marital status, educational level, and age. We retrieved median household income from census tract data based on the participants' addresses. Participants' cognitive performance was assessed using the Rey Auditory Verbal Learning Test (RAVLT) long delay recall and a Rutgers generalization task (Concurrent Discrimination and Transfer Task).

RESULTS

As the number of biological children a woman has had increases, the number of generalization errors also increased, indicating poorer hippocampal-dependent cognitive performance when controlling for age, education, marital status, and median household income. There was no significant relationship between the number of children and performance on a standardized neuropsychological measure of episodic memory (RAVLT), although education was a significant covariate.

DISCUSSION

Generalization tasks may better capture early changes in cognitive performance in older African American women who have had children than standardized neuropsychological assessments. This finding may be explained by the fluctuations in estrogen associated with having children. Future studies should explore how these findings can be applied to protecting cognitive function and preventing Alzheimer's disease in older African American women who have had children.

Hormone Replacement Therapy and Alzheimer's Disease: Current State of Knowledge and Implications for Clinical Use

Alzheimer's disease (AD) is a progressive neurodegenerative disorder responsible for over half of dementia cases, with two-thirds being women. Growing evidence from preclinical and clinical studies underscores the significance of sex-specific biological mechanisms in shaping AD risk. While older age is the greatest risk factor for AD, other distinct biological mechanisms increase the risk and progression of AD in women including sex hormones, brain structural differences, genetic background, immunomodulation and vascular disorders. Research indicates a correlation between declining estrogen levels during menopause and an increased risk of developing AD, highlighting a possible link with AD pathogenesis. The neuroprotective effects of estrogen vary with the age of treatment initiation, menopause stage, and type. This review assesses clinical and observational studies conducted in women, examining the influence of estrogen on cognitive function or addressing the ongoing question regarding the potential use of hormone replacement therapy (HRT) as a preventive or therapeutic option for AD. This review covers recent literature and discusses the working hypothesis, current use, controversies and challenges regarding HRT in preventing and treating age-related cognitive decline and AD. The available evidence indicates that estrogen plays a significant role in influencing dementia risk, with studies demonstrating both beneficial and detrimental effects of HRT. Recommendations regarding HRT usage should carefully consider the age when the hormonal supplementation is initiated, baseline characteristics such as genotype and cardiovascular health, and treatment duration until this approach can be more thoroughly investigated or progress in the development of alternative treatments can be made.

Associations of reproductive factors and exogenous estrogens with global and domain-specific cognition in later life

INTRODUCTION

Few studies have comprehensively examined the impact of reproductive factors (i.e., reproductive window, parity, hormonal contraception [HC], and menopausal hormone therapy [MHT]) on global and domain-specific cognition in later life.

METHODS

We studied a population-based sample of 2458 women (median age 74.2 years) residing in Olmsted County, Minnesota; participants underwent a clinical evaluation and comprehensive cognitive testing.

RESULTS

The length of a woman's reproductive window was not associated with cognition. Higher parity was associated with greater cognitive decline in all domains. Ever HC use was associated with less decline in all domains. Ever MHT use was associated with greater decline in global cognition and all domain-specific z-scores except visuospatial; results were driven by women who initiated MHT 5 or more years after menopause. Additional adjustments for APOE and vascular-related covariates did not attenuate the results.

DISCUSSION

Multiple reproductive risk factors are associated with cognitive decline in later life.

HIGHLIGHTS

The length of a woman's reproductive window was not associated with cognition longitudinally. Greater parity was associated with greater cognitive decline longitudinally. Ever HC use was associated with less decline in global cognition and all domain-specific z-scores longitudinally (all p < 0.01). Ever MHT use was associated with greater decline in global cognition and all domain-specific z-scores except visuospatial longitudinally (all p < 0.01). The greatest cognitive decline was among women who initiated MHT more than 5 years after menopause.

Very Early-Life Risk Factors for Developing Dementia: Evidence From Full Population Registers

OBJECTIVES

Very early-life conditions are recognized as critical for healthy brain development. This study assesses early-life risk factors for developing dementia. In the absence of historical medical birth records, we leverage an alternative full population approach using demographic characteristics obtained from administrative data to derive proxy indicators for birth complications and unfavorable birth outcomes. We use proxy variables to investigate the impact of early-life risk factors on dementia risk.

METHODS

We use administrative individual-level data for full cohorts born 1932-1950 in Sweden with multigenerational linkages. Records on hospitalization and mortality are used to identify dementia cases. We derive 3 birth risk factors based on demographic characteristics: advanced maternal age, narrow sibling spacing, and twin births, and apply survival analysis to evaluate long-term effects on dementia risk. We control for confounding using multiple indicators for socio-economic status (SES), including parental surnames, and by implementing a sibling design. As comparison exposure, we add low education from the 1970 Census.

RESULTS

The presence of at least 1 birth risk factor increases dementia risk (HR = 1.059; 95% CI: 1.034, 1.085). The occurrence of twin births poses a particularly heightened risk (HR = 1.166; 95% CI: 1.084, 1.255).

DISCUSSION

Improvements to the very early-life environment hold significant potential to mitigate dementia risk. A comparison to the influence of low education on dementia (the largest known modifiable risk factor) suggests that demographic birth characteristics are of relevant effect sizes. Our findings underscore the relevance of providing assistance for births experiencing complications and adverse health outcomes to reduce dementia cases.