Does parity matter in women's risk of dementia? A COSMIC collaboration cohort study

Impact of the South African Child Support Grant on memory decline and dementia probability in rural and low-income mothers, 2014-2021

INTRODUCTION

Aging populations across sub-Saharan Africa are rapidly expanding, leading to an increase in the burden of Alzheimer's disease and related dementias (ADRD). Cash transfer interventions are one plausible mechanism to combat ADRD at a population-level in low-income settings. We exploited exogenous variation in eligibility for South Africa's Child Support Grant (CSG) to estimate the longitudinal association between potential CSG benefit and cognitive trajectories in rural mothers with <10 children (n = 1090).

METHODS

South Africa's CSG delivers monthly cash payments to primary caregivers, predominantly mothers, to offset the costs associated with child rearing. This study implemented a quasi-experimental design using data (2014-2022) from a rural, low-income cohort in the Agincourt research area, South Africa. We fit linear mixed effects models and generalized linear models to estimate the association of potential CSG benefit per eligible child with memory decline and dementia probability, respectively. We stratified all models by the mother's total number of children (1-4 and 5-9) and examined effect modification by household wealth and the mother's education level.

RESULTS

Having above median CSG per eligible child was associated with higher baseline memory scores (β = 0.12 SD units, 95% CI = 0.02, 0.22) but steeper memory decline (β = -0.02 SD units, 95% CI = -0.04, -0.00) compared to below median CSG. Within stratified analyses, this effect was primarily observed among mothers with 5-9 children. No associations were observed between potential CSG per eligible child and dementia probability.

CONCLUSIONS

Our findings support the use of large-scale cash transfers as a promising intervention to promote healthy cognitive aging in mid-life women within rural, low-income settings. However, we found evidence that the CSG in its current structure may not be sufficient support for women to sustain measurable cognitive benefits over the long-term.

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.

Exploring the parity paradox: Differential effects on neuroplasticity and inflammation by APOEe4 genotype at middle age

Female sex and Apolipoprotein E (APOE) ε4 genotype are top non-modifiable risk factors for Alzheimer's disease (AD). Although female-unique experiences like parity (pregnancy and motherhood) have positive effects on neuroplasticity at middle age, previous pregnancy may also contribute to AD risk. To explore these seemingly paradoxical long-term effects of parity, we investigated the impact of parity with APOEε4 genotype by examining behavioural and neural biomarkers of brain health in middle-aged female rats. Our findings show that primiparous (parous one time) hAPOEε4 rats display increased use of a non-spatial cognitive strategy and exhibit decreased number and recruitment of new-born neurons in the ventral dentate gyrus of the hippocampus in response to spatial working memory retrieval. Furthermore, primiparity and hAPOEε4 genotype synergistically modulate inflammatory markers in the ventral hippocampus. Collectively, these findings demonstrate that previous parity in hAPOEε4 rats confers an added risk to present with reduced activity and engagement of the hippocampus as well as elevated pro-inflammatory signaling, and underscore the importance of considering female-specific factors and genotype in health research.

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.

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.

Roadmap for maternal behavior research in domestic dogs: lessons from decades of laboratory rodent work

Maternal behavior research in laboratory rats has revealed important behavioral and neurobiological mechanisms governing the onset, maintenance and decline of maternal behavior. However, the extent to which these mechanisms are evolutionarily conserved across species is less clear. This manuscript proposes that examining these mechanisms in dogs may be a viable approach to test their generality and help bridge the gap between rodent and human research, as domestic dogs show greater individual differences and exhibit more human-like maternal characteristics than rodents. These aspects represent advantages over rodent models, which in turn allow systems biological approaches not available in rodents. Additionally, domestic dogs share similar social environments with humans, suffer from the same mental disorders as humans, and can be treated with the same medications. This paper begins with a summary of key findings and theoretical developments from decades of rat maternal behavior research, followed by a literature review of the extant maternal behavior research on dogs and related methodology, highlighting the unique behavioral characteristics of dog maternal behavior and similarities and differences from rat maternal behavior. Finally, several knowledge gaps in dog maternal behavior research, as well as the future research in this area is discussed. It concludes that research on dog maternal behavior will not only advance our understanding of the universality of the neurobiological and behavioral mechanisms in maternal behavior, but also improve our understanding of risk factors associated with postpartum mental disorders.

Child support grant expansion and cognitive function among women in rural South Africa: Findings from a natural experiment in the HAALSI cohort

BACKGROUND

Cash transfers are a promising but understudied intervention that may protect cognitive function in adults. Although South Africa has a rapidly ageing population, little is known about the nature of association between cash transfers and cognitive function in this setting.

OBJECTIVES

We leveraged age-eligibility expansions to South Africa's Child Support Grant (CSG) to investigate the association between duration of CSG eligibility and cognitive function of biological mothers of child beneficiaries in South Africa.

METHODS

We analysed 2014/2015 baseline data from 944 women, aged 40-59 years with at least one CSG-eligible child, enrolled in the population-representative HAALSI cohort in Agincourt, South Africa. Duration of CSG eligibility for each mother was calculated based on the birth dates of all their children and the CSG age-eligibility expansion years (2003-2012). Cognitive function was measured using a cognitive battery administered at the HAALSI baseline interview. Linear regression was used to estimate the association between duration of CSG eligibility, dichotomized as low (≤10 years) and high (>10 years) eligibility, and cognitive function z-scores of the mothers.

RESULTS

High vs. low duration of CSG eligibility, was associated with higher cognitive function z-scores in the full sample [β: 0.15 SD units; 95% CI: 0.04, 0.26; p-value = 0.01]. In mothers with one to four lifetime children, but not five or more, high vs. low duration of CSG eligibility, was associated with higher cognitive function z-scores [β: 0.19 SD units; 95% CI: 0.05, 0.34, p-value = 0.02].

CONCLUSION

Government cash transfers given to support raising children may confer substantial protective effects on the subsequent cognitive function of mothers. Further studies are needed to understand how parity may influence this relationship. Our findings bring evidence to policymakers for designing income supplementation programmes to promote healthy cognitive ageing in low-income settings.

Effects of reproductive experience on cost-benefit decision making in female rats

Many individuals undergo mating and/or other aspects of reproductive experience at some point in their lives, and pregnancy and childbirth in particular are associated with alterations in the prevalence of several psychiatric disorders. Research in rodents shows that maternal experience affects spatial learning and other aspects of hippocampal function. In contrast, there has been little work in animal models concerning how reproductive experience affects cost-benefit decision making, despite the relevance of this aspect of cognition for psychiatric disorders. To begin to address this issue, reproductively experienced (RE) and reproductively naïve (RN) female Long-Evans rats were tested across multiple tasks that assess different forms of cost-benefit decision making. In a risky decision-making task, in which rats chose between a small, safe food reward and a large food reward accompanied by variable probabilities of punishment, RE females chose the large risky reward significantly more frequently than RN females (greater risk taking). In an intertemporal choice task, in which rats chose between a small, immediate food reward and a large food reward delivered after a variable delay period, RE females chose the large reward less frequently than RN females. Together, these results show distinct effects of reproductive experience on different forms of cost-benefit decision making in female rats, and highlight reproductive status as a variable that could influence aspects of cognition relevant for psychiatric disorders.

Cellular and molecular signatures of motherhood in the adult and ageing rat brain

Pregnancy is marked by robust changes, including brain changes to volume, structure, connectivity and neuroplasticity. Although some brain changes are restricted to pregnancy and the postpartum, others are long-lasting. Few studies have examined possible mechanisms of these changes or the effects of multiple pregnancies. We characterized various cellular and molecular signatures of parity (nulliparous, primiparous, biparous) in the rat hippocampus. We investigated density of neural stems cells (Sox2), microglia (Iba-1) and levels of a synaptic protein (PSD-95), cell signalling pathways, neuroinflammation, and the tryptophan-kynurenine (TRP-KYN) pathway, one week after weaning their pups from the last pregnancy (age of dam: seven months) and in middle-age (age of dam: 13 months). Parity increased PSD-95 levels in both age groups and prevented the age-related decrease in neural stem cell density observed in nulliparous rats. Biparity increased cell signalling phosphoproteins (pp70S6K, S6RP) and number of microglia in the dentate gyrus, regardless of age. Parity resulted in transient changes to the TRP-KYN system. Thus, previous parity has lasting effects on synaptic plasticity with fewer lasting effects on inflammation and cell signalling phosphoproteins in the whole hippocampus.

Prospective observational studies on nutrition intake and the incidence of cognitive impairment in middle-aged and older adults: A protocol for systematic review and meta-analysis

INTRODUCTION

According to several studies, a specific dietary pattern can reduce the risk of dementia and cognitive impairment. However, the robustness of these results has not been tested. The study intends to investigate the association between nutrition intake and cognitive impairment in middle-aged and older adults (≥45-years) and provide reliable, evidence-based references for healthcare decision-makers, researchers, and policymakers.

REVIEW QUESTION

Are the dietary characteristics of community-dwelling adults (≥45-years) associated with the occurrence of cognitive impairment?

OBJECTIVES

The primary objective of this protocol is to synthesize the longitudinal observational evidence on the relationship between nutrition intake patterns and the incidence of cognitive impairment in middle-aged and older adults (≥45-years), and to provide detailed dietary recommendations for the prevention of cognitive impairment in this population.

METHODS AND ANALYSIS

Cohort studies conducted among adults (≥45-years) will be included. The following electronic databases will be searched for relevant records published by July 2023, with a restriction on language to English: Pubmed, Medline, Embase, Web of science, Cochrane Library. The studies will be selected, the data will be extracted, and the bias risk will be assessed by two independent investigators. The Meta-analysis of Observational Studies in Epidemiology guidelines will be followed to summarize observational studies, and the protocol will adhere to the recommendations from the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols 2015 statement. Endnote X9 will be used to manage data screening. We will use Review Manager 5.4 and Stata 16.0 to conduct data analysis, and a random-effects model will be applied to pool clinically homogenous studies. The results will be presented based on the form of nutrition intake. For assessing publication bias, Egger's test and visual inspection of funnel plots will be utilized.

ETHICS AND DISSEMINATION

As this study does not involve primary data, ethical approval is not required. The final report will be published in a peer-reviewed journal.

PROSPERO REGISTRATION NUMBER

A registration number of DOI 10.17605/OSF.IO/NAKC3 was assigned to it on October 15, 2022 on Prospero.

Beyond sex differences: short- and long-term effects of pregnancy on the brain

Growing attention has been directed to the inclusion of females in neuroscience studies, and to the importance of studying sex as a biological variable. However, how female-specific factors such as menopause and pregnancy, affect the brain remains understudied. In this review, we use pregnancy as a case in point of a female-unique experience that can alter neuroplasticity, neuroinflammation, and cognition. We examine studies in both humans and rodents indicating that pregnancy can modify neural function in the short term, as well as alter the trajectory of brain aging. Furthermore, we discuss the influence of maternal age, fetal sex, number of pregnancies, and presence of pregnancy complications on brain health outcomes. We conclude by encouraging the scientific community to prioritize researching female health by recognizing and including factors such as pregnancy history in research.

Associations between parenthood and dementia in men and women: biology or confounding?

BACKGROUND

High parity and extremes of age at first birth have been linked with increased dementia risk in women, with exposure to pregnancy-associated physiological changes proposed as an explanation. However, confounding by socioeconomic and lifestyle factors could also produce such associations, whereby men would share similar patterns of association. We investigated whether these associations hold for both sexes.

METHODS

In a cohort study including all women (N = 2,222,638) and men (N = 2,141,002) ≥ 40 years of age in 1994-2017 in Denmark, we used Cox regression to evaluate associations between number of children, age at first birth, and dementia risk separately for women and men.

RESULTS

During follow-up, 81,413 women and 53,568 men (median age at diagnosis, 83.3 and 80.3 years, respectively) developed dementia. Compared with having one child, having two or more children was associated with modest decreases in overall dementia risk in both sexes (hazard ratio [HR] range 0.82-0.91, P_{difference men vs. women} = 0.07). Although the associations between childlessness and overall dementia risk differed statistically for men and women, the association magnitudes differed only slightly (HR_men 1.04, 95% confidence interval [CI] 1.01-1.06; HR_women 0.99, 95% CI 0.97-1.01; P = 0.002). Associations between age at becoming a parent and overall dementia were also similar for women and men, with the exception of older (≥ 40 years) first-time parents (HR_men 1.00, 95% CI 0.96-1.05; HR_women 0.92, 95% CI 0.86-0.98; P = 0.01). With few exceptions, sub-analyses by dementia subtype and timing of onset also revealed similar patterns and effect magnitudes for women and men.

CONCLUSIONS

Associations between number of children, age at becoming a parent, and dementia risk were similar for both sexes. Lifestyle and socioeconomic factors are more likely to explain the observed associations than normal pregnancy-related physiological changes.

Walking for Cognitive Health: Previous Parity Moderates the Relationship Between Self-Reported Walking and Cognition

BACKGROUND

Older females show greater cognitive gains from physical activity (PA) than males, which may be related to long-term consequences of female-specific reproductive events (eg, pregnancy) on cognitive health.

METHODS

To determine whether previous parity could moderate the relationship between PA and cognitive decline in older women, we conducted secondary analyses of data from the Health, Aging, and Body Composition Study. We tested whether the association between average PA over 10 years and cognition (Modified Mini-Mental State Examination [3MS]) and executive functioning (digit symbol substitution test [DSST]) over 10 years varied by previous parity (nulliparity, low parity, medium parity, and grand multiparity). An analysis of covariance was performed with cognition (average and change over 10 years) as the dependent variables, parity as a categorical predictor, average PA as a continuous predictor, and a set of relevant covariates.

RESULTS

Significant interactions were found between PA and parity group for all 4 comparisons: average 3MS (p = .014), average DSST (p = .032), change in 3MS (p = .016), and change in DSST (p = .017). Simple slope analyses indicated the positive relationship between PA and average 3MS and DSST was only significant in the nulliparity and grand multiparity groups, and the positive relationship between PA and change in 3MS and DSST was only significant in the grand multiparity group.

CONCLUSION

The findings suggest the relationship between self-reported walking and cognitive performance was strongest in the groups at risk for cognitive decline and dementia, the nulliparous and grand multiparous groups.

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

While much previous work linking fertility history with late-life cognition has focused on a narrow set of cognitive measures and/or has used modest sample sizes in the analysis, our paper expands the size and scope of these linkages by analyzing cognitive function across five domains and precisely estimating gendered patterns between men and women. Results point to important gendered associations between parity and cognition: having children is likely associated with better cognitive function for fathers in all five domains. However, mothers show worse cognitive function in some domains (i.e., numeric memory, prospective memory, and fluid intelligence) than childless women. We explore the possibility of confounding in these associations and rule out the effects of genetic cognitive ability on fertility. We also find that adding controls for educational attainment differ by gender-strengthening associations between parity and cognition for men and largely eliminating them for women. The findings support previous work done on how life course contexts may link to the risk of dementia or cognitive impairment, highlighting parity as potential protective or risk factors to parents' cognitive health. The use of five cognitive domains yields variations in results, giving implications on measure selection of cognitive function and calling for replicated work covering more cognitive domains.

Child Support Grant expansion and cognitive function among women in rural South Africa: findings from a natural experiment in HAALSI cohort

Cash transfers are a promising but understudied intervention that may protect cognitive function in adults by promoting their cognitive reserve. South Africa has a rapidly ageing population, however, less is known about the nature of association between cash transfers and cognitive function in this setting. We leveraged natural experiments from Child Support Grant (CSG) age-eligibility expansions to investigate the association between duration of CSG eligibility and cognitive function among biological mothers of child beneficiaries in South Africa. We analysed 2014/2015 baseline data from 944 women, aged 40 - 59 years with at least one CSG-eligible child, enrolled in the HAALSI cohort in Agincourt, South Africa. Duration of CSG eligibility for each mother was calculated based on the birth dates of all their children and the CSG age eligibility expansion years. Cognitive function was measured using a cognitive battery administered to the mothers at baseline interview. Linear regression was used to estimate the association between duration of CSG eligibility, dichotomized as low (≤10 years) and high (>10 years) eligibility, and cognitive function z-scores of the mothers. Our study finds that high duration of CSG eligibility, compared to low, was associated with higher cognitive function z-scores in the full sample [β: 0.15 SD; 95% CI: 0.04, 0.26; p-value = 0.01]. In mothers with one to four lifetime children, but not five or more, high duration of CSG eligibility, compared to low, was associated with higher cognitive function z-scores [β: 0.19 SD; 95% CI: 0.05, 0.34, p-value = 0.02]. Government cash transfers given to support raising children may confer substantial protective effect on cognitive function of mothers in their mid-life. Further studies are needed to understand how parity may influence this relationship. Our findings bring evidence to policymakers for designing income supplementation programmes to promote healthy cognitive ageing in low-income settings.

Fertility experiences and later-life cognitive function among older adults in China

OBJECTIVES

The relationship between fertility history and human health has long fascinated scholars; however, whether there is a link between number of children and cognitive function in older adults remains unclear. We investigated the associations between parity and the timing of first and last births with the cognitive function of older adults over 65.

METHODS

The mini-mental state examination (MMSE) was selected as a tool to measure cognitive function. We analyzed data on 5847 older adults in rural and urban communities in China from the 2018 Chinese Longitudinal Healthy Longevity Survey using ordinary least squares. To further explore the transmission mechanism, we also conducted a mediating effect analysis.

RESULTS

We found a negative association between number of children and cognitive function in older adults. Compared with older adults with four children, the MMSE scores of older adults with more than five children decreased significantly, and the score of older adults with zero to three children increased. Further, a late age at first birth (≥35) and a late age at last birth (≥35) were negatively associated with cognitive function. We also found that the associations between parity and cognition might be partly explained by variations in health.

CONCLUSION

Our analyses provided evidence from China to support the link between fertility history and cognitive function that has been observed in previous international studies: We suggest that high parity (≥5) is negatively associated with cognitive function.

The expectant brain-pregnancy leads to changes in brain morphology in the early postpartum period

There is growing evidence that pregnancy may have a significant impact on the maternal brain, causing changes in its structure. To investigate the patterns of these changes, we compared nulliparous women (n = 40) with a group of primiparous women (n = 40) and multiparous mothers (n = 37) within 1-4 days postpartum, using voxel-based and surface-based morphometry (SBM). Compared with the nulliparous women, the young mothers showed decreases in gray matter volume in the bilateral hippocampus/amygdala, the orbitofrontal/subgenual prefrontal area, the right superior temporal gyrus and insula, and the cerebellum. These pregnancy-related changes in brain structure did not predict the quality of mother-infant attachment at either 3 or 12 weeks postpartum nor were they more pronounced among the multiparous women. SBM analyses showed significant cortical thinning especially in the frontal and parietal cortices, with the parietal cortical thinning likely potentiated by multiple pregnancies. We conclude that, compared with the brain of nulliparous women, the maternal brain shows widespread morphological changes shortly after childbirth. Also, the experience of pregnancy alone may not be the underlying cause of the adaptations for mothering. As regards the exact biological function of the changes in brain morphology, longitudinal research will be needed to draw any definitive conclusions.

Reproductive factors and the risk of incident dementia: A cohort study of UK Biobank participants

BACKGROUND

Women's reproductive factors have been associated with the risk of dementia; however, these findings remain uncertain. This study aimed to examine the risk of incident all-cause dementia associated with reproductive factors in women and the number of children in both sexes and whether the associations vary by age, socioeconomic status (SES), smoking status, and body mass index (BMI) in the UK Biobank.

METHODS AND FINDINGS

A total of 273,240 women and 228,957 men without prevalent dementia from the UK Biobank were included in the analyses. Cox proportional hazard regressions estimated hazard ratios (HRs) for reproductive factors with incident all-cause dementia. Multiple adjusted models included age at study entry, SES, ethnicity, smoking status, systolic blood pressure, BMI, history of diabetes mellitus, total cholesterol, antihypertensive drugs, and lipid-lowering drugs. Over a median of 11.8 years follow-up, 1,866 dementia cases were recorded in women and 2,202 in men. Multiple adjusted HRs ((95% confidence intervals (CIs)), p-value) for dementia were 1.20 (1.08, 1.34) (p = 0.016) for menarche <12 years and 1.19 (1.07, 1.34) (p = 0.024) for menarche >14 years compared to 13 years; 0.85 (0.74, 0.98) (p = 0.026) for ever been pregnant; 1.43 (1.26, 1.62) (p < 0.001) for age at first live birth <21 compared to 25 to 26 years; 0.82 (0.71, 0.94) (p = 0.006) for each abortion; 1.32 (1.15, 1.51) (p = 0.008) for natural menopause at <47 compared to 50 years; 1.12 (1.01, 1.25) (p = 0.039) for hysterectomy; 2.35 (1.06, 5.23) (p = 0.037) for hysterectomy with previous oophorectomy; and 0.80 (0.72, 0.88) (p < 0.001) for oral contraceptive pills use. The U-shaped associations between the number of children and the risk of dementia were similar for both sexes: Compared with those with 2 children, for those without children, the multiple adjusted HR ((95% CIs), p-value) was 1.18 (1.04, 1.33) (p = 0.027) for women and 1.10 (0.98, 1.23) (p = 0.164) for men, and the women-to-men ratio of HRs was 1.09 (0.92, 1.28) (p = 0.403); for those with 4 or more children, the HR was 1.14 (0.98, 1.33) (p = 0.132) for women and 1.26 (1.10, 1.45) (p = 0.003) for men, and the women-to-men ratio of HRs was 0.93 (0.76, 1.14) (p = 0.530). There was evidence that hysterectomy (HR, 1.31 (1.09, 1.59), p = 0.013) and oophorectomy (HR, 1.39 (1.08, 1.78), p = 0.002) were associated with a higher risk of dementia among women of relatively lower SES only. Limitations of the study include potential residual confounding and self-reported measures of reproductive factors, as well as the limited representativeness of the UK Biobank population.

CONCLUSIONS

In this study, we observed that some reproductive events related to shorter cumulative endogenous estrogen exposure in women were associated with higher dementia risk, and there was a similar association between the number of children and dementia risk between women and men.

Hormones and neuroplasticity: A lifetime of adaptive responses

Major life transitions often co-occur with significant fluctuations in hormones that modulate the central nervous system. These hormones enact neuroplastic mechanisms that prepare an organism to respond to novel environmental conditions and/or previously unencountered cognitive, emotional, and/or behavioral demands. In this review, we will explore several examples of how hormones mediate neuroplastic changes in order to produce adaptive responses, particularly during transitions in life stages. First, we will explore hormonal influences on social recognition in both males and females as they transition to sexual maturity. Next, we will probe the role of hormones in mediating the transitions to motherhood and fatherhood, respectively. Finally, we will survey the long-term impact of reproductive experience on neuroplasticity in females, including potential protective effects and risk factors associated with reproductive experience in mid-life and beyond. Ultimately, a more complete understanding of how hormones influence neuroplasticity throughout the lifespan, beyond development, is necessary for understanding how individuals respond to life changes in adaptive ways.

Association of bilateral oophorectomy and menopause hormone therapy with mild cognitive impairment: the REDLINC X study

BACKGROUND

Dementia is a major public health problem. Estrogen is a regulator of the central nervous system and its deficit could be involved in cognitive decline in older women.

OBJECTIVE

This study aimed to evaluate the association of bilateral oophorectomy, menopause hormone therapy (MHT) and other factors on mild cognitive impairment (MCI).

METHOD

The case-control study included 941 otherwise healthy postmenopausal women aged 60 years and over from six Latin American countries. Personal and family data were recorded and MCI was assessed using the Montreal Cognitive Assessment test (MoCA).

RESULTS

Average age, years of education and body mass index were 66.1 ± 5.8 years, 12.4 ± 5.0 years and 26.0 ± 4.3 kg/m², respectively. A total of 30.2% had undergone bilateral oophorectomy and 40.3% had used MHT. A total of 232 women (24.7%) had MCI. The prevalence of MCI was higher in women with intact ovaries and non-MHT users as compared to MHT users (29.3% vs. 11.7% [odds ratio (OR) 0.32; 95% confidence interval (CI) 0.20-0.51]). Among oophorectomized women, MCI prevalence was higher among non-MHT users as compared to MHT users (45.2% vs. 12.8% [OR 0.18; 95% CI 0.10-0.32]). Logistic regression analysis determined that the variables associated with MCI were age >65 years (OR 1.69; 95% CI 1.20-2.38), parity (having >2 children; OR 1.69; 95% CI 1.21-2.37), bilateral oophorectomy (OR 1.56; 95% CI 1.09-2.24), hypertension (OR 1.41; 95% CI 1.01-1.96), being sexually active (OR 0.56; 95% CI 0.40-0.79), education >12 years (OR 0.46; 95% CI 0.32-0.65) and MHT use (OR 0.31; 95% CI 0.21-0.46).

CONCLUSION

Age, parity, bilateral oophorectomy and hypertension are independent factors associated with MCI; contrary to this, higher educational level, maintaining sexual activity and using MHT are protective factors.

Remodeling of the maternal gut microbiome during pregnancy is shaped by parity

BACKGROUND

The maternal microbiome has emerged as an important factor in gestational health and outcome and is associated with risk of preterm birth and offspring morbidity. Epidemiological evidence also points to successive pregnancies-referred to as maternal parity-as a risk factor for preterm birth, infant mortality, and impaired neonatal growth. Despite the fact that both the maternal microbiome and parity are linked to maternal-infant health, the impact of parity on the microbiome remains largely unexplored, in part due to the challenges of studying parity in humans.

RESULTS

Using synchronized pregnancies and dense longitudinal monitoring of the microbiome in pigs, we describe a microbiome trajectory during pregnancy and determine the extent to which parity modulates this trajectory. We show that the microbiome changes reproducibly during gestation and that this remodeling occurs more rapidly as parity increases. At the time of parturition, parity was linked to the relative abundance of several bacterial species, including Treponema bryantii, Lactobacillus amylovorus, and Lactobacillus reuteri. Strain tracking carried out in 18 maternal-offspring "quadrads"-each consisting of one mother sow and three piglets-linked maternal parity to altered levels of Akkermansia muciniphila, Prevotella stercorea, and Campylobacter coli in the infant gut 10 days after birth.

CONCLUSIONS

Collectively, these results identify parity as an important environmental factor that modulates the gut microbiome during pregnancy and highlight the utility of a swine model for investigating the microbiome in maternal-infant health. In addition, our data show that the impact of parity extends beyond the mother and is associated with alterations in the community of bacteria that colonize the offspring gut early in life. The bacterial species we identified as parity-associated in the mother and offspring have been shown to influence host metabolism in other systems, raising the possibility that such changes may influence host nutrient acquisition or utilization. These findings, taken together with our observation that even subtle differences in parity are associated with microbiome changes, underscore the importance of considering parity in the design and analysis of human microbiome studies during pregnancy and in infants. Video abstract.