A primer on common analytic concerns in psychoneuroimmunology: Alternatives and paths forward

On the pursuit of reproducibility: the importance of large sample sizes in psychoimmunology

Peripheral inflammatory markers (PIMs), such as C-reactive protein (CRP) or white blood cell count (WBC), have been associated with depression severity in meta-analyses and large cohort studies. However, in typically-sized psychoimmunology studies (N < 200) that explore associations between PIMs and neurobiological/psychosocial constructs related to depression and studies that examine less-studied PIMs (e.g., interferon gamma), significant concerns about reproducibility of results exist. For the well-characterized association between PIMs (CRP/WBC) and depression severity, we examined statistical errors as a function of sample size in a large community cohort (n = 24,550). We further assessed how statistical errors varied as related to analytic decisions (e.g., number of covariates) and characteristics related to study design (e.g., relationships within subgroups of patients). Only large samples (e.g., n = 1000 to n = 10,000) were sufficiently powered to detect PIM-depression associations and minimized overestimation of effect sizes (e.g., effect size inflation), and greater sample sizes were required as more covariates were included in analytic models. Moderately sized samples (n > 500) generally ensured the correct directionality of effect sizes (e.g., low rates of sign reversal). Sample sizes required for 80% power also varied widely depending on study design characteristics (e.g., N = 350 to N = 10,000+). Typically-sized psychoimmunology studies examining PIM-depression associations (N < 200) are likely underpowered and at high risk of overestimation of effect sizes. Study design characteristics also notably influence power and statistical error rates. Use of large sample sizes (e.g., N > 7000) and consideration of analytic decisions (e.g., number/choice of covariates) will maximize reproducibility of psychoimmunology studies related to depression to enhance development of treatments for depression or to help understand pathophysiological mechanisms of depression.

Early adversity and inflammation at midlife: the moderating role of internalizing psychopathology

BACKGROUND

Childhood adversity has been associated with increased peripheral inflammation in adulthood. However, not all individuals who experience early adversity develop these inflammatory outcomes. Separately, there is also a link between various internalizing emotional distress conditions (e.g. depression, anxiety, and fear) and inflammation in adulthood. It is possible the combination of adult emotional distress and past childhood adversity may be uniquely important for explaining psychopathology-related immune dysfunction at midlife.

METHODS

Using data from the Midlife in the United States (MIDUS) study (n = 1255), we examined whether internalizing, defined as past 12-month emotional distress symptomatology and trait neuroticism, moderated associations between childhood adversity and heightened inflammation in adulthood. Using latent variable modeling, we examined whether transdiagnostic or disorder-specific features of emotional distress better predicted inflammation.

RESULTS

We observed that childhood adversity only predicted adult inflammation when participants also reported adult internalizing emotional distress. Furthermore, this moderation effect was specific to the transdiagnostic factor of emotional distress rather than the disorder-specific features.

CONCLUSIONS

We discuss the possibility that adult internalizing symptoms and trait neuroticism together may signal the presence of temporally stable vulnerabilities that amplify the impact of childhood adversity on midlife immune alterations. The study highlights the importance of identifying emotional distress in individuals who have experienced childhood adversity to address long-term immune outcomes and enhance overall health.

Interpersonal stressors predicting inflammation in adolescents: Moderation by emotion regulation and heart rate variability?

This study assessed interpersonal stressors (peer adversity and parental rejection) as predictors of adolescents' circulating inflammatory markers, while examining emotion regulation and parasympathetic nervous system activity (at rest, reactivity, and recovery) as potential protective moderators. Data were collected in a Belgian cohort of adolescents in 2017 (n=185, 51.4 % boys, 10-18 y) and 2018 (n=98), and included serum inflammatory markers (CRP, TNFα, IFNγ, IL-6, IL-8 and IL-10), peer adversity, parental rejection, emotion regulation and heart rate variability (RMSSD-HRV, at rest and in 2018 also in response to a Trier Social Stress Test). Contrary to the hypothesis, interpersonal stressors were negatively related to TNFα (in 2017 and 2018), IFNγ (in 2017 and longitudinally) and IL-6 (in 2018). In 23 % of the tested associations, HRV at rest was a significant moderator: the negative stressor-inflammation associations were present only among adolescents with low HRV resting values. No significant moderation by HRV reactivity or recovery was detected. After correction for multiple testing, all above-mentioned significant findings disappeared. These unexpected findings may suggest that the positive association between stress exposure and circulating markers of inflammation is not yet detectable in adolescence and perhaps becomes evident only later in life.

Longitudinal associations between dimensions of maltreatment and internalizing symptoms in late adolescence: The role of inflammation during the COVID-19 pandemic

Childhood adversity and depression have been linked with heightened inflammation. However, few longitudinal studies examine how dimensions of maltreatment (i.e., abuse and neglect) differentially impact pathways to heightened inflammation and internalizing symptoms. The present study examined effects of abuse and neglect on (1) internalizing symptoms through inflammation, and (2) on inflammation through internalizing symptoms across 3 years of adolescence in the context of the COVID-19 pandemic. In a sample of 78 adolescents, significant indirect effects revealed that childhood abuse, not neglect, significantly predicted future internalizing symptoms, which predicted future heighted C-reactive protein (CRP). Using prospective longitudinal data, these findings emphasize the importance of examining distinct forms of maltreatment in understanding the developmental pathways connecting early adversity, internalizing symptoms, and inflammation.

Incorporating causal inference perspectives into psychoneuroimmunology: A simulation study highlighting concerns about controlling for adiposity in immunopsychiatry

Psychoneuroimmunology and immunopsychiatry are quickly approaching a critical point where the clinical translatability of their evidence base will be tested. To maximize chances for translational success, we believe researchers must adopt causal inference techniques that augment the causal relevance of estimates given theorized causal structures. To illustrate the utility of incorporating causal inference perspectives into psychoneuroimmunology, we applied directed acyclic graphs and a combination of empirical and simulated data to demonstrate the consequences of controlling for adiposity when testing the association between inflammation and depression under the plausible causal structure of increases in adipose tissue leading to greater inflammation that in turn promotes depression. Effect size estimates were pulled from a dataset combining the Midlife in the United States 2 (MIDUS-2) and MIDUS Refresher datasets. Data were extracted and used to simulate data reflecting an adiposity → inflammation → depression causal structure. Next, a Monte Carlo simulation study with 1,000 iterations and three sample size scenarios (Ns = 100, 250, and 500) was conducted testing whether controlling for adiposity when estimating the relation between inflammation and depression influenced the precision of this estimate. Across all simulation scenarios, controlling for adiposity reduced precision of the inflammation → depression estimate, suggesting that researchers primarily interested in quantifying inflammation → depression associations should not control for adiposity. This work thus underscores the importance of incorporating causal inference approaches into psychoneuroimmunological research.

Mediation of the Association Between Vascular Risk Factors and Depressive Symptoms by C-Reactive Protein

Background

This study examined whether C-reactive protein (CRP), a marker of low-grade systemic inflammation, mediates the association between vascular risk factor (VRF) burden and depressive symptoms.

Methods

We drew on the prospective design of the UK Biobank to include participants with longitudinal data on VRF burden, CRP, and depressive symptoms. Total, direct, and indirect effects were estimated using regression-based mediation models while controlling for confounding by sociodemographic factors, baseline CRP, and baseline depression. Sensitivity analyses probed the robustness of results to unmeasured confounding.

Results

We analyzed data from 10,470 participants from the UK Biobank (mean age = 56.75 years at baseline). Net of covariates, VRFs at baseline were associated with higher depressive symptoms at follow-up (total effect = 0.099; 95% CI, 0.002-0.163). CRP mediated this association (indirect effect = 0.010; 95% CI, 0.004-0.017), accounting for 10.0% (95% CI, 0.3%-30.0%) of the total effect of VRF burden on depressive symptoms. Exploratory analyses suggested that the total and indirect effects pertained to somatic depressive symptoms (tiredness and appetite).

Conclusions

These results suggest that inflammation-promoting effects of VRFs may contribute to depressive symptoms in mid- and later life. However, the mediating pathway via CRP explains only a small part of the association between VRFs and depression after accounting for important covariates and may pertain to specific depressive symptoms. Future studies leveraging similar longitudinal designs are needed to further disentangle the time-varying effects between VRFs, inflammation, and certain depressive symptoms while addressing important confounders.

Age and professional experience as determinants of the utilization of psychoneuroimmunological research in clinical practice: An exploratory study

The immune system is affected by psychosocial stimuli and plays a major role in the development of various diseases. Psychoneuroimmunology (PNI)-based interventions may positively influence the disease course; however, the impact of PNI research findings on clinical practice differs depending on the medical specialties involved. A comprehensive overview of the use of PNI research findings in clinical practice is currently lacking. This exploratory study aimed to provide insight into the dissemination of PNI research findings and their practical applications among clinical practitioners. Data was collected from 50 physicians using an ad hoc online questionnaire. We invited participants to take part in our online survey via an article in the DocCheck Newsletter, a German-language newsletter for physicians. Bivariate nonparametric correlation analysis (Spearman correlation) were used to explore the relationship between independent variables (age, sex, medical specialty, professional experience, and clinical environment) and dependent variables (six questionnaire items concerned with awareness, relevance, and utilization of PNI concepts). While 46% of respondents believed that PNI research findings were relevant to patient treatment, only 22% used PNI-based interventions as part of their therapeutic regimen. Furthermore, 90% of participants could not refer their patients to therapists offering PNI-based interventions. Moderately positive correlations were identified between the increasing age (rs = .48, P < .001) and increasing amount of professional experience (rs = .34, P = .02) of study participants and awareness of the theoretical foundations of PNI research. Although there is some awareness of PNI among medical practitioners, there appears to be a clear barrier inhibiting the implementation of research findings in current treatment practices. Therefore, it is necessary to examine the impact of increasing age and professional experience on the utilization of PNI-based interventions in patient care.