H4K20me3, H3K4me2 and H3K9me2 mediate the effect of ER on prognosis in breast cancer

Previous studies have indicated that histone methylations act as mediators in the relationship between oestrogen receptor (ER) and breast cancer prognosis, yet the mediating role has never been assessed. Therefore, we investigated seven histone methylations (H3K4me2, H3K4me3, H3K9me1, H3K9me2, H3K9me3, H3K27me3 and H4K20me3) to determine whether they mediate the prognostic impact of ER on breast cancer. Tissue microarrays were constructed from 1045 primary invasive breast tumours, and the expressions of histone methylations were examined by immunohistochemistry. Multifactorial logistic regression was used to analyse the associations between ER and histone methylations. Cox proportional hazard model was performed to assess the relationship between histone methylations and breast cancer prognosis. The mediation effects of histone methylations were evaluated by model-based causal mediation analysis. High expressions of H3K9me1, H3K9me2, H3K4me2, H3K27me3, H4K20me3 were associated with ER positivity, while high expression of H3K9me3 was associated ER negativity. Higher H3K9me2, H3K4me2 and H4K20me3 levels were associated with better prognosis. The association between ER and breast cancer prognosis was most strongly mediated by H4K20me3 (29.07% for OS; 22.42% for PFS), followed by H3K4me2 (11.5% for OS; 10.82% for PFS) and least by H3K9me2 (9.35% for OS; 7.34% for PFS). H4K20me3, H3K4me2 and H3K9me2 mediated the relationship between ER and breast cancer prognosis, which would help to further elucidate the impact of ER on breast cancer prognosis from an epigenetic perspective and provide new ideas for breast cancer treatment.

Larger hypothalamic subfield volumes in patients with chronic insomnia disorder and relationships to levels of corticotropin-releasing hormone

The hypothalamus is a well-established core structure in the sleep-wake cycle. While previous studies have not consistently found whole hypothalamus volume changes in chronic insomnia disorder (CID), differences may exist at the smaller substructural level of the hypothalamic nuclei. The study aimed to investigate the differences in total and subfield hypothalamic volumes, between CID patients and healthy controls (HCs) in vivo, through an advanced deep learning-based automated segmentation tool. A total of 150 patients with CID and 155 demographically matched HCs underwent T1-weighted structural magnetic resonance scanning. We utilized FreeSurfer v7.2 for automated segmentation of the hypothalamus and its five nuclei. Additionally, correlation and causal mediation analyses were performed to investigate the association between hypothalamic volume changes, insomnia symptom severity, and hypothalamus-pituitary-adrenal (HPA) axis-related blood biomarkers. CID patients exhibited larger volumes in the right anterior inferior, left anterior superior, and left posterior subunits of the hypothalamus compared to HCs. Moreover, we observed a positive association between blood corticotropin-releasing hormone (CRH) levels and insomnia severity, with anterior inferior hypothalamus (a-iHyp) hypertrophy mediating this relationship. In conclusion, we found significant volume increases in several hypothalamic subfield regions in CID patients, highlighting the central role of the HPA axis in the pathophysiology of insomnia.

The role of breastfeeding support in racial/ethnic disparities in breastfeeding practices

BACKGROUND

Persistent racial/ethnic disparities in breastfeeding practices in the United States are well documented but the underlying causes remain unclear. While racial/ethnic disparities are often intertwined with socioeconomic disparities in breastfeeding, studies suggest that lack of breastfeeding support from family, health care organizations and workplaces may contribute to racial/ethnic disparities in breastfeeding rates. No studies have investigated the extent to which racial/ethnic disparities in breastfeeding practices can be explained by breastfeeding support.

METHODS

We used survey data from participants of a federal nutrition assistance program in Los Angeles County, the most populous county in the United States, to examine causal mechanisms underlying racial/ethnic disparities in breastfeeding in five groups: Spanish-speaking Latina, English-speaking Latina, Non-Hispanic White (NHW), Non-Hispanic Black (NHB) and Non-Hispanic Asian (NHA). Applying causal mediation analysis, this study estimated the proportion of racial/ethnic differences in breastfeeding ('any' breastfeeding, i.e., partial or exclusive) rates at 6 months that could be explained by differential access to breastfeeding support from family, birth hospitals and workplaces.

RESULTS

NHB and English-speaking Latina mothers were less likely, and Spanish-speaking Latina mothers more likely to breastfeed through 6 months than NHW mothers. Lack of breastfeeding support from family, hospitals and workplaces accounted for approximately 68% of the difference in any breastfeeding rates at 6 months between NHW and NHB mothers and 36% of the difference between NHW and English-speaking Latina mothers.

CONCLUSION

These findings highlight the importance of improving support from family, hospitals and workplaces for breastfeeding mothers to reduce racial/ethnic disparities in breastfeeding.

Influence of preterm birth on the association between gestational diabetes mellitus and childhood developmental vulnerability: a causal mediation analysis

BACKGROUND

Epidemiological studies examining the direct and indirect effects of gestational diabetes mellitus (GDM) on offspring early childhood developmental vulnerability are lacking. Therefore, the aims of this study were to estimate the direct and indirect effects of GDM (through preterm birth) on early childhood developmental vulnerability.

METHODS

We conducted a retrospective population-based cohort study on the association between gestational diabetes mellitus and early childhood developmental vulnerability in children born in Western Australia (WA) using maternal, infant and birth records from the Midwives Notification, Hospitalizations, Developmental Anomalies, and the Australian Early Development Census (AEDC) databases. We used two aggregated outcome measures: developmentally vulnerable on at least one AEDC domain (DV1) and developmentally vulnerable on at least two AEDC domains (DV2). Causal mediation analysis was applied to estimate the natural direct (NDE), indirect (NIE), and total (TE) effects as relative risks (RR).

RESULTS

In the whole cohort (n = 64,356), approximately 22% were classified as DV1 and 11% as DV2 on AEDC domains. Estimates of the natural direct effect suggested that children exposed to GDM were more likely to be classified as DV1 (RR = 1.20, 95% CI: 1.10-1.31) and DV2 (RR = 1.34, 95% CI: 1.19-1.50) after adjusting for potential confounders. About 6% and 4% of the effect of GDM on early childhood developmental vulnerability was mediated by preterm birth for DV1 and DV2, respectively.

CONCLUSION

Children exposed to gestational diabetes mellitus were more likely to be developmentally vulnerable in one or more AEDC domains. The biological mechanism for these associations is not well explained by mediation through preterm birth.

Effects of intimate partner violence and homophobic bullying on ART adherence among young Thai men who have sex with men: a causal mediation analysis

Background

Adherence to antiretroviral therapy is crucial in determining health outcomes and secondary HIV transmission for people living with HIV/AIDS. Young men who have sex with men (YMSM) living with HIV are often challenged by the prevailing experiences of psychosocial stressors, such as intimate partner violence and homophobic bullying, which may negatively affect their HIV care engagement.

Methods

This study is the first to utilize a prospective cohort design (N= 185) involving YMSM living with HIV in Thailand. We examined the effects of intimate partner violence and homophobic bullying on ART adherence. We also tested the mediating effect of depression on the relationship between intimate partner violence and homophobic bullying on ART adherence.

Results

We found that intimate partner violence (AOR: 2.58, 95% CI: 1.13, 5.42) and homophobic bullying (AOR: 2.40, 95% CI: 1.26, 4.48) were associated with subsequent ART nonadherence. Moreover, depression partially mediated 17.4% (95% CI: 0.75%, 56%) of the effect of homophobic bullying on ART nonadherence.

Conclusions

The results suggest that tailored interventions to optimize ART adherence should address the impacts of intimate partner violence and homophobic bullying for HIV+ YMSM. The screening and subsequent treatment of depression alone may not be sufficient to address the effects of intimate partner violence, homophobic bullying, and possibly other MSM-specific psychosocial stressors on ART adherence.

A methodological study of exposome based on an open database: Association analysis between exposure to metal mixtures and hyperuricemia

BACKGROUND

Exposome recognizes that humans are constantly exposed to multiple environmental factors, and elucidating the health effects of complex exposure mixtures places greater demands on analytical methods.

OBJECTS

We aimed to explore the association between mixed exposure to metals and hyperuricemia (HUA), and highlight the potential of explainable machine learning (EML) and causal mediation analysis (CMA) for application in the analysis of exposome data.

METHODS

Pre-pandemic data from the National Health and Nutrition Examination Survey (NHANES) 2011-2020 and a total of 13780 individuals were included. We first used traditional statistical models (multiple logistic regression (MLR) and restricted cubic spline regression (RCS)) and EML to explore associations between mixed metals exposures and HUA, followed by the CMA using the 4-way decomposition method to analyze the interaction and mediation effects among BMI or estimated glomerular filtration rate (eGFR), metals and HUA.

RESULTS

The prevalence of HUA was 18.91% (2606/13780). The MLR showed that mercury (Q4 vs Q1: OR = 1.08, 95% CI:1.02-1.14) and lead (Q4 vs Q1: OR = 1.23, 95% CI:1.13-1.34) were generally positively associated with HUA. Higher concentrations of lead, mercury, selenium and manganese were associated with the increased odds of HUA, and BMI and eGFR were the top two variables attributable to the risk of developing HUA in the EML. Subgroup analyses from the MLR and EML consistently demonstrated the positive relationship between exposure to lead, mercury and selenium in participants with BMI <25 kg/m2 and BMI ≥30 kg/m2. BMI mediated 32.12% of the association between lead exposure and HUA, and the interaction between BMI and lead accounted for 3.88% of the association in the CMA.

CONCLUSIONS

Heavy metals can increase the HUA risk and BMI or eGFR can mediate and interact with metals to cause HUA. Future studies based on exposome can attempt to utilize the EML and CMA.

An Introduction to Causal Mediation Analysis With a Comparison of 2 R Packages

Traditional mediation analysis, which relies on linear regression models, has faced criticism due to its limited suitability for cases involving different types of variables and complex covariates, such as interactions. This can result in unclear definitions of direct and indirect effects. As an alternative, causal mediation analysis using the counterfactual framework has been introduced to provide clearer definitions of direct and indirect effects while allowing for more flexible modeling methods. However, the conceptual understanding of this approach based on the counterfactual framework remains challenging for applied researchers. To address this issue, the present article was written to highlight and illustrate the definitions of causal estimands, including controlled direct effect, natural direct effect, and natural indirect effect, based on the key concept of nested counterfactuals. Furthermore, we recommend using 2 R packages, 'medflex' and 'mediation', to perform causal mediation analysis and provide public health examples. The article also offers caveats and guidelines for accurate interpretation of the results.

Pre-pregnancy body mass index and risk of maternal or infant complications with gestational diabetes mellitus as a mediator: A multicenter, longitudinal cohort study in China

AIMS

We explored the complex relationships between pre-pregnancy body mass index (pBMI) and maternal or infant complications and the mediating role of gestational diabetes mellitus (GDM) in these relationships.

METHODS

Pregnant women from 24 hospitals in 15 different provinces of China were enrolled in 2017 and followed through 2018. Propensity score-based inverse probability of treatment weighting, logistic regression, restricted cubic spline models, and causal mediation analysis were utilized. In addition, the E-value method was used to evaluate unmeasured confounding factors.

RESULTS

A total of 6174 pregnant women were finally included. Compared to women with a normal pBMI, obese women had a higher risk for gestational hypertension (odds ratio [OR] = 5.38, 95% confidence interval [CI]: 3.48-8.34), macrosomia (OR = 2.65, 95% CI: 1.83-3.84), and large for gestational age (OR = 2.05, 95% CI: 1.45-2.88); 4.73% (95% CI: 0.57%-8.88%), 4.61% (95% CI: 0.51%-9.74%), and 5.02% (95% CI: 0.13%-10.18%) of the associations, respectively, were mediated by GDM. Underweight women had a high risk for low birth weight (OR = 1.42, 95% CI: 1.15-2.08) and small for gestational age (OR = 1.62, 95% CI: 1.23-2.11). Dose-response analyses indicated that 21.0 kg/m² may be the appropriate tipping point pBMI for risk for maternal or infant complications in Chinese women.

CONCLUSION

A high or low pBMI is associated with the risk for maternal or infant complications and partly mediated by GDM. A lower pBMI cutoff of 21 kg/m² may be appropriate for risk for maternal or infant complications in pregnant Chinese women.

Association between residential greenness and all-cause mortality and the joint mediation effect of air pollutants among old people with disability: A prospective cohort study

BACKGROUND

Residential greenness offers health benefits to old people, but evidence of its association with the health of old people with disability is scarce. Moreover, due to the limited mobility of this vulnerable population, air pollutants may play an indispensable mediating role in that association, which however remains understudied.

OBJECTIVES

This study aimed to investigate the association between residential greenness and all-cause mortality risk and the joint mediation effect of air pollutants among old people with disability.

METHODS

A total of 34,075 old people with disability were included in the Chengdu Long-term Care Insurance cohort. Participants' residential greenness exposure was measured by an enhanced vegetation index within the 500 m buffer zone (EVI_500m). Causal mediation analysis was conducted to assess the total effect (TE) of residential greenness and the natural indirect effect (NIE) through PM_2.5, CO, NO₂, SO₂, and O₃ on all-cause mortality.

RESULTS

The TE of EVI_500m on the all-cause mortality risk in overall participants showed negative, which, decreased from the 2^nd quartile (HR = 0.93, 95 % CI: 0. 91, 0.95) to the 4^th quartile (HR = 0.81, 95 % CI: 0.76, 0.85); the NIE through the five air pollutants also decreased from the 2^nd quartile (HR = 0.96, 95 % CI: 0.95, 0.98) to the 4^th quartile (HR = 0.90, 95 % CI: 0.88, 0.93), with the proportion mediated decreased from 48 % to 44 %. The stronger TE or NIE were observed in participants aged <80 years old, men, with mild-moderate disability, and having outdoor experience every week.

CONCLUSION

Exposure to residential greenness was associated with a decreased risk of mortality, partially through the pathways of air pollutants, which varied by age, sex, degree of disability, and frequency of weekly outdoors. Our findings would provide evidence to develop aging-friendly cities.

Evaluating the Mediating Role of Recall of Intervention Knowledge in the Relationship Between a Peer-Driven Intervention and HIV Risk Behaviors Among People Who Inject Drugs

Peer-driven interventions can be effective in reducing HIV injection risk behaviors among people who inject drugs (PWID). We employed a causal mediation framework to examine the mediating role of recall of intervention knowledge in the relationship between a peer-driven intervention and subsequent self-reported HIV injection-related risk behavior among PWID in the HIV Prevention Trials Network (HPTN) 037 study. For each intervention network, the index participant received training at baseline to become a peer educator, while non-index participants and all participants in the control networks received only HIV testing and counseling; recall of intervention knowledge was measured at the 6-month visit for each participant, and each participant was followed to ascertain HIV injection-related risk behaviors at the 12-month visit. We used inverse probability weighting to fit marginal structural models to estimate the total effect (TE) and controlled direct effect (CDE) of the intervention on the outcome. The proportion eliminated (PE) by intervening to remove mediation by the recall of intervention knowledge was computed. There were 385 participants (47% in intervention networks) included in the analysis. The TE and CDE risk ratios for the intervention were 0.47 [95% confidence interval (CI): 0.28, 0.78] and 0.73 (95% CI: 0.26, 2.06) and the PE was 49%. Compared to participants in the control networks, the peer-driven intervention reduced the risk of HIV injection-related risk behavior by 53%. The mediating role of recall of intervention knowledge accounted for less than 50% of the total effect of the intervention, suggesting that other potential causal pathways between the intervention and the outcome, such as motivation and skill, self-efficacy, social norms and behavior modeling, should be considered in future studies.

The mediating effects of depression, anxiety, and rapid eye movement sleep behavior disorder on the association between dopaminergic replacement therapy and impulse control disorders in Parkinson's disease

OBJECTIVES

This study aims to longitudinally explore whether and how rapid eye movement sleep behavior disorder (RBD), depression, and anxiety mediate the association between dopaminergic replacement therapy (DRT) and impulse control disorders (ICDs) in patients with Parkinson's disease (PD).

METHODS

Subjects were selected from the Parkinson's Progression Markers Initiative. After excluding missing data, 268, 223, 218, 238, and 219 patients with PD diagnosed at 12, 24, 36, 48, and 60 months prior, respectively, were included. We used the Questionnaire for Impulsive-Compulsive Disorders, RBD Screening Questionnaire, Geriatric Depression Scale, and State-Trait-Anxiety Inventory to assess ICBs, RBD, depression, and anxiety, respectively. We constructed three causal mediation analysis models to infer potential contingent pathways from DRT to ICD mediated by depression, anxiety, and RBD separately.

RESULTS

DRT was associated with an increased risk of PD incidence. Aggravation of ICDs was partly explained by improvements in depression (the average causal mediation effect accounted for 8.0% of the total effect) and RBD (the average causal mediation effect of RBD accounted for 16.4% of the total effect). This suggested that anxiety (the average causal mediation effect accounted for 12.7% of the total effect) plays a mediating role.

CONCLUSIONS

Focusing on changes in RBD, depression, and anxiety associated with hyperdopaminergic status should be an essential part of strategies to prevent ICDs in patients with Parkinson's disease.

Complete effect decomposition for an arbitrary number of multiple ordered mediators with time-varying confounders: A method for generalized causal multi-mediation analysis

Causal mediation analysis is advantageous for mechanism investigation. In settings with multiple causally ordered mediators, path-specific effects have been introduced to specify the effects of certain combinations of mediators. However, most path-specific effects are unidentifiable. An interventional analog of path-specific effects is adapted to address the non-identifiability problem. Moreover, previous studies only focused on cases with two or three mediators due to the complexity of the mediation formula in a large number of mediators. In this study, we provide a generalized definition of traditional path-specific effects and interventional path-specific effects with a recursive formula, along with the required assumptions for nonparametric identification. Subsequently, a general approach is developed with an arbitrary number of multiple ordered mediators and with time-varying confounders. All methods and software proposed in this study contribute to comprehensively decomposing a causal effect confirmed by data science and help disentangling causal mechanisms in the presence of complicated causal structures among multiple mediators.

A causal mediation analysis

Large inequalities in health and well-being exist between people with and without disability, in part due to poor socio-economic circumstances, and potentially also related to societal factors including issues associated with accessibility and participation. To better understand the contribution of societal factors, we used a unique longitudinal survey of disability in Great Britain to quantify the extent to which barriers to participation contribute to poorer health and well-being. We used data from 2354 individuals who participated in three waves of the Life Opportunities Survey between 2009 and 2014 and compared five health and well-being outcomes (self-rated health, anxiousness, life satisfaction, life worth, happiness) between adults who acquired an impairment and those who remained disability-free. Causal mediation analysis was conducted to quantify how much of the effect of disability acquisition on each outcome was explained by barriers to participation in employment, economic life, transport, community, leisure and civic activities, social contact, and accessibility. People who recently acquired a disability had poorer health and well-being compared to people with no disability. Barriers to participation explained 15% of inequalities in self-rated health, 28% for anxiousness, 32% for life satisfaction, 37% for life worth, and 70% for happiness. A substantial proportion of the inequalities in health and well-being experienced by people with recently acquired disability were socially produced, driven by barriers to participation in different life domains. Furthermore, there was evidence that barriers to participation mediated the effect of well-being measured to a greater extent than the more clinically aligned measures, self-reported health and anxiousness. These findings highlight modifiable factors amenable to public health interventions that could lead to substantial improvements in health and well-being for people with disability.

High cardiovascular disease risk-associated with the incidence of Type 2 diabetes among prediabetics

BACKGROUND

Prediabetes is a risk factor for developing Type 2 diabetes mellitus (T2D). We report on the first cohort study of the association between high cardiovascular diseases (CVD) risk with the incidence of T2D in prediabetics. First, estimate the direct effect of developing T2D on patients with prediabetes who have high CVDs risk; and 2) assess the potential increased risk of developing T2D mediated by statins.

METHODS

We conducted a population-based cohort study using a subset of data from the Canadian Primary Care Sentinel Surveillance Network (CPCSSN) from 2000 to 2015. Cox proportional hazards (PH) regressions were conducted to estimate our primary outcome, which is the time to T2D among patients with prediabetes.

RESULTS

From the 4995 filtered prediabetic participants identified between 2000 and 2015, 2800 participants were diagnosed with high CVDs risk scores as measured by the Framingham risk score. 2195 participants were non-high CVDs risk controls. The covariate-adjusted hazard ratio (HR) of 1.24 [95% confidence interval (CI), 1.10-1.31] for T2D by CVDs risk among prediabetics was observed. The total effect of CVDs risk on developing T2D was decomposed to a natural direct effect of high CVDs risk HR= 1.18 [95% CI, 1.01-1.48] and an indirect effect through statin therapy of HR= 1.06 [95% CI, 0.97-1.30].

CONCLUSION

Patients with prediabetes and high CVDs risk had a 24% higher chance of developing T2D. The high CVDs risk effect was mediated by statin therapy. Regular monitoring and counselling of prediabetics using statins is likely warranted to prevent the incidence of T2D.

Role of insulin resistance in the association between resting heart rate and type 2 diabetes: A prospective study

BACKGROUND

Elevated resting heart rate (RHR) is a predictor of incident type 2 diabetes (T2D). Insulin resistance is thought to play a role in this association; however, the extent to which insulin resistance mediates this association is unclear.

METHODS

1309 Japanese individuals without diabetes were recruited during 2009-2012 and followed for 5 years, of whom 78 developed T2D, as diagnosed by the 75 g oral glucose tolerance test. Supine RHR was measured by electrocardiography. Using logistic regression analysis, we examined the association between RHR and incident T2D, and interaction with the homeostasis model assessment of insulin resistance (HOMA-IR) index. Causal mediation analysis was applied to decompose the effect of RHR on the outcome and estimate the proportion mediated by the HOMA-IR index.

RESULTS

The sex- and age-adjusted cumulative incidence rate of T2D increased with increasing RHR. After adjustment for sex, age, waist circumference, current smoking status, alcohol use, habitual exercise, and cardiovascular disease medications, individuals with a RHR ≥80 bpm, compared with <60 bpm, showed an increased risk of incident T2D [odds ratio (OR), 2.89; 95 % confidence interval (CI), 1.07 to 7.80]. Multivariate adjusted OR for the total effect per 1 SD increase in RHR on incident T2D was 1.37 (95 % CI, 1.01 to 1.74) in the mediation analysis, and the proportion of the total indirect effect mediated by the HOMA-IR index was 27.5 % (95 % CI, 1.5 to 53.5).

CONCLUSIONS

Approximately 30 % of the effect of RHR on incident T2D was explained by the indirect effect of insulin resistance.

The role of frailty in the association between depression and fall risk among older adults

OBJECTIVES

Although there is a recognized association between depression and greater fall risk among older adults, the mechanisms explaining this association are unclear. This study evaluated the role of frailty, a common geriatric syndrome, in determining greater risk of falls among older adults with depression.

METHOD

We used longitudinal data from three biennial waves of the Health and Retirement Study (HRS; 2010-2014). The sample included community-dwelling survey respondents age ≥ 65 who participated in objective physiological measures. Major Depression (MD) was measured using Composite International Diagnostic Interview for depression short form. Frailty was measured using criteria outlined in the frailty phenotype model. Causal mediation analysis was used to differentiate the direct effect of depression and indirect effect mediated by frailty on falls, fall injuries, and multiple falls.

RESULTS

Major depression was associated with significantly greater odds of experiencing a fall (OR: 1.91; 95% CI: 1.31, 2.77), fall injury (OR: 1.86; 95% CI: 1.17, 2.95), and multiple falls (OR: 2.26; 95% CI: 1.52, 3.37) over a two-year period. Frailty was a significant mediator of the effects of depression on falls and multiple falls, accounting for approximately 18.9% and 21.3% of the total effects, respectively. We found no evidence of depression-frailty interaction. Sensitivity analyses showed that results were robust to unmeasured confounding and alternative operationalizations of depression.

CONCLUSION

Frailty explains a significant proportion of increased likelihood of falls among older adults with depression. Treatment and management of frailty symptoms may be an important components of fall prevention among older adults with depression.

Chronic hypertension, perinatal mortality and the impact of preterm delivery: a population-based study

OBJECTIVES

To estimate the association between chronic hypertension and perinatal mortality and to evaluate the extent to which risks are impacted by preterm delivery.

DESIGN

Cross-sectional analysis.

SETTING

United States, 2015-18.

POPULATION

Singleton births (20-44 weeks of gestation).

EXPOSURE

Chronic hypertension, defined as elevated blood pressure diagnosed before pregnancy or recognised before 20 weeks of gestation.

MAIN OUTCOMES AND MEASURES

We derived the risk of perinatal mortality in relation to chronic hypertension from Poisson models, adjusted for confounders. The impacts of misclassification and unmeasured confounding were assessed. Causal mediation analysis was performed to quantify the impact of preterm delivery on the association.

RESULTS

Of the 15 090 678 singleton births, perinatal mortality rates were 22.5 and 8.2 per 1000 births in chronic hypertensive and normotensive pregnancies, respectively (adjusted risk ratio 2.05, 95% CI 2.00-2.10). Corrections for exposure misclassification and unmeasured confounding biases substantially increased the risk estimate. Although causal mediation analysis revealed that most of the association of chronic hypertension on perinatal mortality was mediated through preterm delivery, the perinatal mortality rates were highest at early term, term and late term gestations, suggesting that a planned early term delivery at 37-38^6/7  weeks may optimally balance risk in these pregnancies. Additionally, 87% (95% CI 84-90%) of perinatal deaths could be eliminated if preterm deliveries, as a result of chronic hypertension, were preventable.

CONCLUSIONS

Chronic hypertension is associated with increased risk for perinatal mortality. Planned early term delivery and targeting modifiable risk factors for chronic hypertension may reduce perinatal mortality rates.

TWEETABLE ABSTRACT

Maternal chronic hypertension is associated with increased risk for perinatal mortality, largely driven by preterm birth.

Association between a single mother family and childhood undervaccination, and mediating effect of household income: a nationwide, prospective birth cohort from the Japan Environment and Children's Study (JECS)

Background

Although childhood undervaccination among single mother families is a concern for child healthcare, their association is still under debate. This study aimed to investigate the association between maternal marital status and the risk of childhood undervaccination and determine the mediating effect of household income.

Methods

We utilised prospective birth cohort from the Japan Environment and Children’s Study (JECS). Of 104,062 foetal records (children) from 97,413 mothers, 82,462 that included mothers recruited between 2011 and 2014, were analysed. Childhood undervaccination was defined as not having been vaccinated with at least one routine vaccine. A log-binomial regression analysis was used to estimate the risk ratio (RR) for the association between maternal marital status and the risk of childhood undervaccination. A causal mediation analysis was further performed to investigate the proportion of the association mediated by household income.

Results

Among 82,462 children, 3188 and 79,274 had unmarried and married mothers, respectively. Childhood undervaccination was observed in 1053 (33.0%) and 16,901 (21.3%) children of unmarried and married mothers, respectively. Maternal marital status was associated with a higher risk of childhood undervaccination (adjusted risk ratio [aRR], 1.34; 95% confidence interval [CI], 1.27 to 1.41). Compared with married and older mothers, both unmarried and older (aRR, 1.54; 95% CI, 1.35 to 1.77) and unmarried and younger (aRR, 1.66; 95% CI, 1.54 to 1.79) mothers were associated with a higher risk of childhood undervaccination. The causal mediation analysis showed that the proportion mediated by household income was 10.5% (95% CI, 9.9 to 11.0%).

Conclusions

This nationwide, prospective, large-scale birth cohort study found that a household with a single mother was associated with an increased risk of childhood undervaccination, and 10% of this association was explained by household income. These findings underscore the importance of improving the social environment among single mother families, including not only poverty but also working conditions.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12889-022-12511-7.

Role of medical comorbidity in the association between psychiatric disorders and mortality among patients with COVID-19

We examined whether excess chronic medical comorbidity mediated excess COVID-19 inpatient mortality among people with mental disorders in the early phase of the pandemic, a question with important implications for public health and clinical decision-making. Using records of 2599 COVID-19 hospitalized patients, we conducted a formal causal mediation analysis to estimate the extent to which chronic comorbidity mediates the association between mental disorders and COVID-19 mortality. The Odds Ratio (95% CI) for Natural Indirect Effect and Controlled Direct Effect were 1.07(1.02, 1.14) and 1.40 (1.00, 1.95), respectively, suggesting that a large proportion of excess COVID-19 mortality among people with mental disorders may be explained by factors other than comorbidity.

Mediators of neutrophil lymphocyte ratio in the relationship between ondansetron pre-treatment and the mortality of ICU patients on mechanical ventilation: causal mediation analysis from the MIMIC-IV database

AIMS

The mortality of critically ill patients undergoing mechanical ventilation (MV) is high and few strategies are available. We explored the relationship between ondansetron pre-treatment, the neutrophil:lymphocyte ratio (NLR), and platelet:lymphocyte ratio (PLR), and mortality of ventilated patients in the intensive care unit.

METHODS

We developed a retrospective cohort study that involved patients undergoing MV in the Multiparameter Intelligent Monitoring in Intensive Care IV (MIMIC-IV) database. Causal mediation analysis was conducted to assess the relationship of ondansetron use and mortality and explore the potential causal pathway mediated by the NLR or PLR. The primary outcome was 28-day mortality.

RESULTS

A total of 17,927 eligible patients was obtained (5665 had taken ondansetron before MV initiation and 12,262 patients had not). The OR for 28-day mortality for ondansetron use uncorrelated with the mediator (NLR, PLR) was 0.72 (95%CI=0.64-0.81, P <0.001). Ondansetron was also associated with a reduction in 28-day mortality after controlling for the mediator of NLR (OR = 0.98, 95%CI = 0.97-0.99, P < 0.01). For the indirect effect, the NLR could explain 13.47% (95%CI = 8.59-20.54%, P < 0.01) of the impact of ondansetron use on 28-day mortality. The proportion mediated increased to 21.50% (95%CI = 12.36-47.44%, P < 0.01) for 90-day mortality. Adjusted mediation analysis revealed no suggestion of a causal mediation pathway for this effect by the PLR (P = 0.12).

CONCLUSIONS

NLR may play substantial roles in the relationship between ondansetron pre-treatment before initiation of mechanical ventilation and the reduction of death risk in ventilated patients.

Does NAFLD mediate the relationship between obesity and type 2 diabetes risk? evidence from the multi-ethnic study of atherosclerosis (MESA)

PURPOSE

To estimate the effect of obesity on type 2 diabetes (T2DM) risk and evaluate to what extent non-alcoholic fatty liver disease (NAFLD) mediates this association.

METHODS

Data came from 4,522 adults ages 45-84 participating in the Multi-Ethnic Study of Atherosclerosis cohort. Baseline obesity was defined using established BMI categories. NAFLD was measured by CT scans at baseline and incident T2DM defined as fasting glucose ≥126 mg/dL or use of diabetes medications.

RESULTS

Over a median 9.1 years of follow-up between 2000 and 2012, 557 new cases of T2DM occurred. After adjusting for age, sex, race/ethnicity, education, diet and exercise, those with obesity had 4.5 times the risk of T2DM compared to normal weight (hazard ratio [HR] = 4.5, 95% confidence interval [CI]: 3.0, 5.9). The mediation analysis suggested that NAFLD accounted for ~36% (95% CI: 27, 44) of the effect (direct effect HR = 3.2, 95% CI: 2.3, 4.6; indirect effect through NAFLD, HR = 1.4, 95% CI: 1.3, 1.5).

CONCLUSIONS

These data suggest that the association between obesity and T2DM risk is partially explained by the presence of NAFLD. Future studies should evaluate if NAFLD could be an effective target to reduce the effect of obesity on T2DM.

Association between cardiac autonomic function and physical activity in patients at high risk of sudden cardiac death: a cohort study

Background

High levels of physical activity (PA) and heart rate variability (HRV) are associated with cardiovascular benefits in patients with cardiovascular diseases. HRV, representing cardiac autonomic function, is positively associated with PA. However, the impacts of PA and cardiac autonomic function on cardiovascular outcomes were not analysed in the same study population. This lack of evidence supported our hypothesis that PA might contribute to cardiovascular benefits via enhanced cardiac autonomic function.

Methods

Patients with implantable cardioverter defibrillator (ICD) or cardiac resynchronisation therapy defibrillator (CRT-D) implantation were included from the SUMMIT registry. HRV and PA values were assessed during the first 30–60 days post device implantation using a continuous home monitoring system. Causal mediation analysis was conducted to explore the possible mediation function of HRV in the association of PA with long-term cardiac death and all-cause mortality in patients at a high risk of sudden cardiac death.

Results

Over a mean follow-up period of 47.7 months, 63 cardiac deaths (18.9%) and 85 all-cause death events (25.5%) were observed among 342 patients with ICD/CRT-D implantation. A positive linear association between HRV and PA was demonstrated and the β value of HRV was 0.842 (95% confidence interval [CI]: 0.261–1.425, P = 0.005) in the multiple linear regression analysis. Multivariable Cox proportional hazards analysis revealed that high levels of PA (≥11.0%) and HRV (≥75.9 ms) were independent protective factors against cardiac death (PA: hazard ratio [HR] = 0.273; 95% CI, 0.142–0.526, P < 0.001; HRV: HR = 0.224; 95% CI, 0.103–0.489, P < 0.001) and all-cause mortality (PA: HR = 0.299; 95% CI, 0.177–0.505, P < 0.001; HRV: HR = 0.394; 95% CI, 0.231–0.674, P = 0.001). Causal mediation analysis demonstrated partial mediation effects of PA that were mediated through HRV on cardiac death (mediation proportion = 12.9, 95%CI: 2.2–32.0%, P = 0.006) and all-cause mortality (mediation proportion = 8.2, 95%CI: 1.6–20.0%, P = 0.006).

Conclusions

HRV might be a modest mediator in the association between high levels of PA and the reduced risks of cardiac death and all-cause mortality in ICD/CRT-D recipients. This finding supports that enhanced cardiac autonomic function might be one of the underlying mechanisms by which regular PA contributes to cardiovascular benefits.

Antidepressant Use Partially Mediates the Association Between Depression and Risk of Falls and Fall Injuries Among Older Adults

BACKGROUND

The association between depression and fall risk in older adults is recognized, yet the mechanisms underlying this association are unclear. This study estimated the mediating role of antidepressant use in the association between depression and falls and fall injuries.

METHODS

Longitudinal data from the Health and Retirement Study (2004-2006) were linked with medication data from the Prescription Drug Study (2005). The sample included community-dwelling adults aged ≥65 with data on depression and medication use (n = 3565). Depression was measured using 2 independent survey tools: Composite International Diagnostic Interview for depression short form and an 8-item version of the Center for Epidemiological Studies-Depression scale. We used causal mediation analysis to estimate and compare the direct and indirect (mediated by antidepressant use) effects of depression on falls and fall injuries.

RESULTS

Individuals with major depressive disorder were significantly more likely to experience a fall (OR: 1.92; 95% CI: 1.41, 2.62) and a fall injury (OR: 1.67; 95% CI: 1.09, 2.55) over 2 years. Indirect effect estimates showed that antidepressant medication use accounted for approximately 19% and 18% of the association between major depressive disorder and falls and fall injuries, respectively. Results were similar when using an alternative depression measure and when considering only selective serotonin reuptake inhibitor antidepressants.

CONCLUSIONS

Antidepressant use explains a significant proportion, but not a majority, of the association between depression and greater fall risk. Treatment benefits of antidepressants should be considered with, and may outweigh, concerns about increased risk of falls associated with antidepressant use.

Why Does a Growth Mindset Intervention Impact Achievement Differently across Secondary Schools? Unpacking the Causal Mediation Mechanism from a National Multisite Randomized Experiment

The growth mindset or the belief that intelligence is malleable has garnered significant attention for its positive association with academic success. Several recent randomized trials, including the National Study of Learning Mindsets (NSLM), have been conducted to understand why, for whom, and under what contexts a growth mindset intervention can promote beneficial achievement outcomes during critical educational transitions. Prior research suggests that the NSLM intervention was particularly effective in improving low-achieving 9th graders' GPA, while the impact varied across schools. In this study, we investigated the underlying causal mediation mechanism that might explain this impact and how the mechanism varied across different types of schools. By extending a recently developed weighting method for multisite causal mediation analysis, the analysis enhances the external and internal validity of the results. We found that challenge-seeking behavior played a significant mediating role, only in medium-achieving schools, which may partly explain the reason why the intervention worked differently across schools. We conclude by discussing implications for designing interventions that not only promote students' growth mindsets but also foster supportive learning environments under different school contexts.

Trauma-related differences in socio-emotional functioning predict housing and employment outcomes in homeless veterans

RATIONALE

Mental health and substance use disorders are strong risk factors for homelessness. Understanding the role of transdiagnostic factors could help inform efforts to reduce homelessness among veterans with a range of disorders. Homeless veterans have high rates of trauma exposure, which can result in the depletion of social and emotional resources that may contribute to housing and employment stability. In this study, we evaluated the role of problems with emotional lability and interpersonal closeness as transdiagnostic socio-emotional factors that might interfere with efforts to achieve housing and employment stability.

METHODS

The sample consisted of 346 homeless veterans with co-occurring disorders that were admitted to a U.S. Department of Veterans Affairs (VA) residential treatment program between 2004 and 2009. Assessments were conducted at treatment entry (baseline) and two follow-up timepoints (6- and 12-months). Variables used in the current analyses included history of interpersonal trauma exposure, emotional lability and interpersonal closeness at baseline and 6-months, and homelessness and employment problems during follow-up. Data were analyzed using structural equation modeling and counterfactually-defined mediation effects.

RESULTS

Veterans exposed to more trauma types experienced more baseline impairment and less improvement during treatment in emotional lability and interpersonal closeness. Problems with interpersonal closeness mediated 73% of the relationship between exposure to multiple traumas and homelessness, and 32%-61% of the relationship between trauma exposure and employment problems. Emotional lability mediated 36% of the relationship between exposure to multiple traumas and employment problems. Decomposition of indirect pathways revealed that indirect effects were primarily transmitted through changes during treatment, and not baseline levels.

CONCLUSION

Findings support a cumulative effect of trauma on persistence of socio-emotional deficits across treatment, which increased risk of homelessness and employment problems during follow-up. Greater attention and more targeted efforts should be directed at helping trauma-exposed veterans build socio-emotional resources during treatment.

Large-Scale Hypothesis Testing for Causal Mediation Effects with Applications in Genome-wide Epigenetic Studies

In genome-wide epigenetic studies, it is of great scientific interest to assess whether the effect of an exposure on a clinical outcome is mediated through DNA methylations. However, statistical inference for causal mediation effects is challenged by the fact that one needs to test a large number of composite null hypotheses across the whole epigenome. Two popular tests, the Wald-type Sobel's test and the joint significant test using the traditional null distribution are underpowered and thus can miss important scientific discoveries. In this paper, we show that the null distribution of Sobel's test is not the standard normal distribution and the null distribution of the joint significant test is not uniform under the composite null of no mediation effect, especially in finite samples and under the singular point null case that the exposure has no effect on the mediator and the mediator has no effect on the outcome. Our results explain why these two tests are underpowered, and more importantly motivate us to develop a more powerful Divide-Aggregate Composite-null Test (DACT) for the composite null hypothesis of no mediation effect by leveraging epigenome-wide data. We adopted Efron's empirical null framework for assessing statistical significance of the DACT test. We showed analytically that the proposed DACT method had improved power, and could well control type I error rate. Our extensive simulation studies showed that, in finite samples, the DACT method properly controlled the type I error rate and outperformed Sobel's test and the joint significance test for detecting mediation effects. We applied the DACT method to the US Department of Veterans Affairs Normative Aging Study, an ongoing prospective cohort study which included men who were aged 21 to 80 years at entry. We identified multiple DNA methylation CpG sites that might mediate the effect of smoking on lung function with effect sizes ranging from -0.18 to -0.79 and false discovery rate controlled at level 0.05, including the CpG sites in the genes AHRR and F2RL3. Our sensitivity analysis found small residual correlations (less than 0.01) of the error terms between the outcome and mediator regressions, suggesting that our results are robust to unmeasured confounding factors.

The deterioration of oral function and orofacial appearance mediated the relationship between tooth loss and depression among community-dwelling older adults: A JAGES cohort study using causal mediation analysis

BACKGROUND

Depression is a major health problem among older adults, for which previous studies have suggested tooth loss as a risk factor. This study examined the mediating effect of oral function and orofacial appearance in the relationship between tooth loss and depression.

METHODS

This three-year follow-up longitudinal study was based on a self-reported questionnaire targeting community-dwelling older adults aged ≥65 years. We used the incidence of depressive symptoms during follow-up as the outcome, the number of remaining teeth (≥20/≤19) as the exposure, and the deterioration of oral function and orofacial appearance (speaking, smiling, and eating) as mediators. We fitted the logistic regression model including confounders and calculated the natural indirect effect (NIE), natural direct effect, and the proportion mediated (PM) by the deterioration of oral functions by applying the causal mediation analysis framework.

RESULTS

The mean age of the 8,875 participants was 72.7 years (1SD=5.5) and 48.0% were male. Depressive symptoms developed during follow-up in 11.5% of the participants (n=1,024). The incidence for those with ≤19 and ≥20 remaining teeth was 13.1% and 9.2%, respectively. Total effect of fewer remaining teeth (≤19) on depressive symptoms was OR=1.30 (95%CI=1.12-1.51). Difficulty in speaking (NIE OR=1.03, 95%CI=1.00-1.06, PM=12.4%), problems in smiling (NIE OR=1.04, 95%CI=1.01-1.07, PM=16.9%), and difficulty in chewing (NIE OR=1.05, 95%CI=1.02-1.09, PM=21.9%) significantly mediated the relationship.

LIMITATION

Selection bias due to dropout.

CONCLUSION

Deterioration of oral function and orofacial appearance were mediating factors of the mechanism for the relationship between tooth loss and the incidence of depressive symptoms.

Adolescents' relative position in school and educational attainment: The mediating role of educational expectations

This study examines whether and how adolescents' relative deprivation in school is associated with their years of education by incorporating the social comparison perspective into the Wisconsin status attainment model. Using Waves 1, 2, and 4 of the National Longitudinal Study of Adolescent to Adult Health (Add Health), this study finds that adolescents who are positioned at the bottom of the economic hierarchy in school are likely to have up to one less year of education, compared to their counterparts positioned at the top of the hierarchy, when holding other variables constant. Also, by using causal mediation analyses, I find that educational expectations account for more than 20% of the relationship between adolescents' relative deprivation and educational attainment. The sensitivity analyses are conducted to examine how robust the main findings are to the violation of the assumption used in this study. These results provide evidence showing that adolescents' educational outcomes do not only depend on their material resources but also on their relative standing in the economic hierarchy.

Maternal folic acid supplementation mediates the associations between maternal socioeconomic status and congenital heart diseases in offspring

Low maternal socioeconomic status (SES) is considered as a risk factor of congenital heart diseases (CHDs) in offspring. However, the pathways underpinning the SES-CHDs associations are unclear. We assessed if first trimester maternal folic acid supplementation (FAS) is a mediator of the SES-CHDs associations. This case-control study included 8379 CHD cases and 6918 CHD-free controls from 40 participating centers in Guangdong, Southern China, 2004-2016. All fetuses were screened for CHDs using ultrasound and cases were confirmed by echocardiogram. We collected SES and FAS information during face-to-face interview by obstetricians using a structured questionnaire. Low SES was defined as education attainment <12 years, household individual income <3000 Chinese Yuan/person/month or unemployment. FAS referred to at least 0.4 mg of daily folic acid intake over 5 days/week continuously. We used causal mediation analysis to estimate the direct, indirect and proportion mediated by FAS on the SES-CHDs associations adjusted for confounders. Both low maternal income and education were significantly associated with increased risks of CHDs and lower prevalence of FAS. Low maternal FAS prevalence mediated 10% [95%CI:5%,13%] and 3% [95%CI:1%,5%] of the maternal low income-CHDs and the maternal low education-CHDs associations, respectively. In addition, FAS mediated the highest proportion of the associations between income and multiple critical CHDs [46.9%, 95%CI:24.7%,77%] and conotruncal defects [31.5%, 95%CI:17.1%,52.0%], respectively. Maternal FAS partially mediated the SES-CHDs associations, especially among the most critical and common CHDs. Promoting FAS in low SES women of childbearing age may be a feasible intervention to help prevent CHDs.

Air Pollution and Adverse Pregnancy and Birth Outcomes: Mediation Analysis Using Metabolomic Profiles

PURPOSE OF REVIEW

Review how to use metabolomic profiling in causal mediation analysis to assess epidemiological evidence for air pollution impacts on birth outcomes.

RECENT FINDINGS

Maternal exposures to air pollutants have been associated with pregnancy complications and adverse pregnancy and birth outcomes. Causal mediation analysis enables us to estimate direct and indirect effects on outcomes (i.e., effect decomposition), elucidating causal mechanisms or effect pathways. Maternal metabolites and metabolic pathways are perturbed by air pollution exposures may lead to adverse pregnancy and birth outcomes, thus they can be considered mediators in the causal pathways. Metabolomic markers have been used to explain the biological mechanisms linking air pollution and respiratory function, and of arsenic exposure and birth weight. However, mediation analysis of metabolomic markers has not been used to assess air pollution effects on adverse birth outcomes. In this article, we describe the assumptions and applications of mediation analysis using metabolomic markers that elucidate the potential mechanisms of the effects of air pollution on adverse pregnancy and birth outcomes. The hypothesis of mediation along specified pathways can be assessed within the structural causal modeling framework. For causal inferences, several assumptions that go beyond the data-including no uncontrolled confounding-need to be made to justify the effect decomposition. Nevertheless, studies that integrate metabolomic information in causal mediation analysis may greatly improve our understanding of the effects of ambient air pollution on adverse pregnancy and birth outcomes as they allow us to suggest and test hypotheses about underlying biological mechanisms in studies of pregnant women.

Functional relevance of resistance training-induced neuroplasticity in health and disease

Repetitive, monotonic, and effortful voluntary muscle contractions performed for just a few weeks, i.e., resistance training, can substantially increase maximal voluntary force in the practiced task and can also increase gross motor performance. The increase in motor performance is often accompanied by neuroplastic adaptations in the central nervous system. While historical data assigned functional relevance to such adaptations induced by resistance training, this claim has not yet been systematically and critically examined in the context of motor performance across the lifespan in health and disease. A review of muscle activation, brain and peripheral nerve stimulation, and imaging data revealed that increases in motor performance and neuroplasticity tend to be uncoupled, making a mechanistic link between neuroplasticity and motor performance inconclusive. We recommend new approaches, including causal mediation analytical and hypothesis-driven models to substantiate the functional relevance of resistance training-induced neuroplasticity in the improvements of gross motor function across the lifespan in health and disease.

The effect of gender on mental health service use: an examination of mediation through material, social and health-related pathways

PURPOSE

We aimed to understand how much of the gender difference in mental health service use could be due to the joint mediation of employment, behavioural and material factors, social support and mental health need.

METHODS

We used data from employed individuals aged 18-65 years who participated in the 2015-2017 waves of the Household, Income and Labour Dynamics in Australia survey. The exposure (male, female) and confounders were measured in 2015, mediators in 2016 and the outcome-whether a person had seen a mental health professional in the previous year-was measured in 2017. We estimated natural mediation effects using weighted counterfactual predictions from a logistic regression model.

RESULTS

Men were less likely to see a mental health care provider than women. The total causal effect on the risk difference scale was  - 0.045 (95% CI  - 0.056,  - 0,034). The counterfactual of men taking the mediator values of women explained 28% (95% CI 1.7%, 54%) of the total effect, with the natural direct effect estimated to represent an absolute risk difference of  - 0.033 (95% CI  - 0.048,  - 0.018) and the natural indirect effect  - 0.012 (95% CI  - 0.022,  - 0.0027).

CONCLUSION

Gendered differences in the use of mental health services could be reduced by addressing inequalities in health, employment, material and behavioural factors, and social support.

Examining the causal mediating role of brain pathology on the relationship between diabetes and cognitive impairment: the Cardiovascular Health Study

The paper examines whether diabetes mellitus leads to incident mild cognitive impairment and dementia through brain hypoperfusion and white matter disease. We performed inverse odds ratio weighted causal mediation analyses to decompose the effect of diabetes on cognitive impairment into direct and indirect effects, and we found that approximately a third of the total effect of diabetes is mediated through vascular-related brain pathology. Our findings lend support for a common aetiological hypothesis regarding incident cognitive impairment, which is that diabetes increases the risk of clinical cognitive impairment in part by impacting the vasculature of the brain.

Cognitive reserve mediates the severity of certain neuropsychological deficits related to cocaine use disorder

The concept of cognitive reserve (CR) is being considered in the field of substance use disorder (SUD) by observing that there are individuals whose brain alterations are not related to the cognitive symptomatology they present. Our aims were to characterise the possible neuropsychological deficits in a sample of subjects with SUD compared to healthy controls and to determine whether the degree of CR is a mediator in the cognitive functioning of these patients. To perform these objectives, the study involved a sample of subjects with SUD in outpatient treatment and a healthy control group. A CR questionnaire and a comprehensive neuropsychological assessment were administered, and we also collected data related to drug consumption and psychological well-being. The SUD group showed poorer performance compared to the control group in several cognitive domains (attention, declarative memory, executive functions and emotional perception), as well as in psychological comfort. Interestingly, we observed that the deficits found in attention and processing speed were highly mediated by the CR level of the participants, an effect that we did not observe in the rest of the variables registered. Our results suggest that long-term drug consumption leads to cognitive deficits and affects the psychological well-being of the subjects. Moreover, the CR should be taken into account during the assessment and rehabilitation of patients with SUD due to its protective role against certain neuropsychological deficits.

Stein-like estimators for causal mediation analysis in randomized trials

Causal mediation analysis aims to estimate natural direct and natural indirect effects under clearly specified assumptions. Traditional mediation analysis based on Ordinary Least Squares assumes an absence of unmeasured causes to the putative mediator and outcome. When these assumptions cannot be justified, instrumental variable estimators can be used in order to produce an asymptotically unbiased estimator of the mediator-outcome link, commonly referred to as a Two-Stage Least Squares estimator. Such bias removal, however, comes at the cost of variance inflation. A Semi-Parametric Stein-Like estimator has been proposed in the literature that strikes a natural trade-off between the unbiasedness of the Two-Stage Least Squares procedure and the relatively small variance of the Ordinary Least Squares estimator. The Semi-Parametric Stein-Like estimator has the advantage of allowing for a direct estimation of its shrinkage parameter. In this paper, we demonstrate how this Stein-like estimator can be implemented in the context of the estimation of natural direct and natural indirect effects of treatments in randomized controlled trials. The performance of the competing methods is studied in a simulation study, in which both the strength of hidden confounding and the strength of the instruments are independently varied. These considerations are motivated by a trial in mental health, evaluating the impact of a primary care-based intervention to reduce depression in the elderly.

Polygenic liability for schizophrenia predicts shifting-specific executive function deficits and tobacco use in a moderate drinking community sample

Individuals with schizophrenia have higher lifetime rates of substance use disorders than the general population, and research suggests high comorbidity rates may be partially explained by shared genetic influences related to common underlying etiology. Moreover, deficits in executive functions are thought to be central to the diagnosis of schizophrenia and are likewise associated with alcohol and tobacco use. The current study examined the associations between schizophrenia polygenic risk scores and tobacco and alcohol use and the mediation of these associations by executive function sub-domains. Results from the Psychiatric Genomics Consortium's meta-analysis of genome-wide association studies of schizophrenia were used to calculate polygenic risk scores in a sample of moderate drinkers. Schizophrenia risk scores were significantly associated with shifting-specific executive function deficits and tobacco use phenotypes. However, risk scores were not significantly associated with alcohol use and executive functions were not significantly associated with either tobacco or alcohol use. These findings extend previous research by suggesting that genetic risk for schizophrenia may be associated with specific sub-domains of executive function as well as smoking. The lack of a relation with alcohol use suggests genetic factors related to schizophrenia and executive functioning may not influence drinking in a non-disordered, social-drinking sample.

Loneliness as a mediator of the relationship between shame and health problems in young people exposed to childhood violence

RATIONALE

Shame related to childhood violence can be detrimental to mental and physical health. Shame may erode social bonds.

OBJECTIVE

In this study we tested whether loneliness is an important pathway between violence-related shame and health problems.

METHOD

Individuals who reported exposure to childhood violence in a telephone interview survey in 2013 (wave one) were re-contacted 12-18 months later (wave two), as part of a more general survey of the Norwegian adult population. In total, 505 adolescent and young adult participants (mean age = 21 years) responded to questions about violence exposure, violence-related shame, loneliness, anxiety/depression symptoms, and somatic health complaints. We used counterfactually based causal mediation analysis within the structural equation modelling framework to test whether loneliness mediated a potential association between shame and health.

RESULTS

Shame had a profound effect on anxiety/depression symptoms and we identified both direct and indirect effects. Loneliness mediated about one third of the relationship between shame and anxiety/depression symptoms. The relationship between shame and somatic health complaints was weaker in total, but this more modest effect largely occurred indirectly through loneliness.

CONCLUSIONS

Our results add to the literature by highlighting the role of loneliness in the relationship between shame and health. Shame may have the potential to break down social connectedness, with a detrimental effect on health. Clinicians may find it helpful to pay close attention to the way shame regulates social interaction. Preventing social isolation and loneliness may promote good health in violence victims.

Implementation and reporting of causal mediation analysis in 2015: a systematic review in epidemiological studies

Background

Causal mediation analysis is often used to understand the impact of variables along the causal pathway of an occurrence relation. How well studies apply and report the elements of causal mediation analysis remains unknown.

Methods

We systematically reviewed epidemiological studies published in 2015 that employed causal mediation analysis to estimate direct and indirect effects of observed associations between an exposure on an outcome. We identified potential epidemiological studies through conducting a citation search within Web of Science and a keyword search within PubMed. Two reviewers independently screened studies for eligibility. For eligible studies, one reviewer performed data extraction, and a senior epidemiologist confirmed the extracted information. Empirical application and methodological details of the technique were extracted and summarized.

Results

Thirteen studies were eligible for data extraction. While the majority of studies reported and identified the effects of measures, most studies lacked sufficient details on the extent to which identifiability assumptions were satisfied. Although most studies addressed issues of unmeasured confounders either from empirical approaches or sensitivity analyses, the majority did not examine the potential bias arising from the measurement error of the mediator. Some studies allowed for exposure-mediator interaction and only a few presented results from models both with and without interactions. Power calculations were scarce.

Conclusions

Reporting of causal mediation analysis is varied and suboptimal. Given that the application of causal mediation analysis will likely continue to increase, developing standards of reporting of causal mediation analysis in epidemiological research would be prudent.

Causal mediation analysis for longitudinal data with exogenous exposure

Mediation analysis is a valuable approach to examine pathways in epidemiological research. Prospective cohort studies are often conducted to study biological mechanisms and often collect longitudinal measurements on each participant. Mediation formulae for longitudinal data have been developed. Here, we formalize the natural direct and indirect effects using a causal framework with potential outcomes that allows for an interaction between the exposure and the mediator. To allow different types of longitudinal measures of the mediator and outcome, we assume two generalized mixed-effects models for both the mediator and the outcome. The model for the mediator has subject-specific random intercepts and random exposure slopes for each cluster, and the outcome model has random intercepts and random slopes for the exposure, the mediator, and their interaction. We also expand our approach to settings with multiple mediators and derive the mediated effects, jointly through all mediators. Our method requires the absence of time-varying confounding with respect to the exposure and the mediator. This assumption is achieved in settings with exogenous exposure and mediator, especially when exposure and mediator are not affected by variables measured at earlier time points. We apply the methodology to data from the Normative Aging Study and estimate the direct and indirect effects, via DNA methylation, of air pollution, and temperature on intercellular adhesion molecule 1 (ICAM-1) protein levels. Our results suggest that air pollution and temperature have a direct effect on ICAM-1 protein levels (i.e. not through a change in ICAM-1 DNA methylation) and that temperature has an indirect effect via a change in ICAM-1 DNA methylation.