Excess body weight and specific types of depressive symptoms: Is there a mediating role of systemic low-grade inflammation?

Systemic inflammation as a mediator in the link between obesity and depression: Evidence from a nationwide cohort study

BACKGROUND

Obesity and depression are major public health issues with a complex, bidirectional relationship potentially involving systemic inflammation.

METHODS

Using a diverse sample from the National Health and Nutrition Examination Survey (NHANES) (n = 11,324; weighted population = 456,457,366), we examined the associations between obesity, systemic inflammation, and depression. Obesity was classified by Body Mass Index (BMI), depressive symptoms were assessed with the Patient Health Questionnaire-9 (PHQ-9), and systemic inflammation was measured using markers like Neutrophil-to-Lymphocyte Ratio (NLR), Systemic Inflammation Response Index (SIRI), and Systemic Immune-Inflammation Index (SII). Weighted logistic regression models were used to assess relationships between obesity, inflammation, and depression. Linear regression evaluated BMI's association with inflammation markers, and Restricted Cubic Spline (RCS) analysis explored their interrelationships. Subgroup analyses and interaction tests were conducted, and mediation analysis examined the role of inflammation markers in mediating the obesity-depression association.

RESULTS

Class III obesity was associated with higher inflammatory marker levels and increased depression risk. Mediation analysis showed NLR, SIRI, and SII mediated 5.2%, 5.9%, and 6.1% of the obesity-depression relationship.

CONCLUSIONS

Systemic inflammation partially mediates the relationship between obesity and depression.

Risk of severe obesity development: Examining the role of psychological well-being related measures and sociodemographic factors in two longitudinal UK cohort studies

OBJECTIVE

To examine the prospective association between psychological well-being related measures and severe obesity development in young and middle-aged UK adults.

DESIGN

A longitudinal analysis of two cohort studies.

METHODS

We used data from the 1958 National Child Development Study (NCDS) and the 1970 British Cohort Study (BCS) to examine the association between baseline psychological well-being related measures (depressive symptoms, life satisfaction and self-efficacy) and severe obesity development (defined as body mass index - BMI ≥35 kg/m2) and residualized BMI change scores at follow-up. We analysed repeated measures of baseline and follow-up pairs with 6- to 7-year follow-up on average (n = 22,390 and 23,811 observations in NCDS and BCS, respectively) using panel data logistic and linear models controlling for sociodemographic factors. We conducted additional analyses using analytical sample sizes with longer follow-up (16-17 years).

RESULTS

Although a range of sociodemographic factors (e.g., being female, non-married) were associated with increased risk of severe obesity development, we found limited evidence that psychological well-being related measures were associated with severe obesity development across cohorts and pooled analyses. Depressive symptoms, life satisfaction and self-efficacy were, however, associated with relatively small changes in continuous BMI change across analyses, and this tended to be limited to participants without obesity (BMI 18.5 to <30 kg/m2) and not those already living with obesity (BMI 30 to <35 kg/m2) at baseline.

CONCLUSIONS

There is limited evidence that psychological well-being related measures prospectively predict the development of severe obesity. Poorer psychological well-being is associated with modest changes in body weight in individuals without obesity.

Pathways linking BMI trajectories and mental health in an adult population-based cohort: role of emotional eating and body dissatisfaction

BACKGROUND

Overweight and obesity are associated with poor mental health, and the association is bidirectional. Few studies have examined the association between weight change and mental health over time. We aimed to provide further insight into the association between weight gain and mental health, with a focus on emotional eating and body dissatisfaction as mediating factors.

METHODS

Height and weight were self-reported upon registration, and in Spring 2022, 2023, and 2024 in the Specchio cohort (Geneva, Switzerland). BMI trajectories were estimated by (1) mixed-effects models to calculate participants' personal slopes (increase in BMI score per year), and (2) testing the odds of an upward BMI category transition from baseline to last follow-up. The associations of behavioural and psychosocial factors with BMI trajectories (slopes and transitions), and BMI trajectories with mental health outcomes were estimated using regressions adjusted for age, sex, education, and physical health condition. Structural equation modelling was used to test mediating pathways.

RESULTS

Among 7388 participants (59% women, mean age 51 years), factors associated with increasing BMI over 4 years included financial hardship, short sleep duration, less physical activity, more leisure screen time, depressive and anxiety symptoms, and emotional eating (β range [95% CI] = 0.03 [0, 0.05]-0.12 [0.09, 0.15]). Increasing BMI was associated with body dissatisfaction (β = 0.36 [0.33, 0.38]) and poorer quality of life (β = -0.06 [-0.09, -0.03]) at 4-year follow-up after adjustment for anxiety and depressive symptoms at baseline. Emotional eating partly mediated the association between anxiety and depressive symptoms at baseline and increasing BMI, and between financial hardship and increasing BMI. Body dissatisfaction and poorer self-rated health partly mediated the association between increasing BMI and quality of life at follow-up.

CONCLUSIONS

Emotional eating and body dissatisfaction contribute to the association between BMI trajectories and mental health and should be considered in weight management and mental health promotion strategies.

Association between body roundness index and sleep disorder: the mediating role of depression

BACKGROUND

Several studies have indicated a potential association between obesity, depression, and sleep disorders. However, the role of depression in mediating the relationship between obesity and sleep disorders remains unclear. The Body Roundness Index (BRI), a more precise anthropometric measure of obesity than the traditional body mass index (BMI), is particularly effective in assessing body and visceral fat levels. This study examines the relationship between BRI and sleep disorders, with a focus on whether depression influences this association.

METHODS

This study included data from 32,504 participants in the National Health and Nutrition Examination Survey (NHANES) 2005-2018 cycle. The association between BRI and sleep disorders was examined through subgroup analysis, restricted cubic spline (RCS) modeling, threshold effect analysis, and multivariable logistic regression. Furthermore, the predictive capabilities of various anthropometric indices-including BRI, weight-adjusted waist index (WWI), BMI, and weight-on sleep disorder incidence were assessed using Receiver Operating Characteristic (ROC) curve analysis. Finally, a Mediation analysis was also performed to explore the potential role of depression in this relationship.

RESULTS

This study included 32,504 participants, of whom 4,568 reported sleep disorders. After adjusting for all covariates using multivariable logistic regression, each one-unit increase in BRI was associated with a 13% higher prevalence of sleep disorders (OR = 1.13, 95% CI: 1.09, 1.16) and an 8% higher prevalence of depression (OR = 1.08, 95% CI: 1.05, 1.11). Similar results were obtained when BRI was divided into tertiles, with a significant trend (P for trend < 0.05). RCS and threshold effect analyses revealed a nonlinear relationship between BRI and sleep disorder prevalence, with a breakpoint of 3.508. The ROC curve analysis revealed that BRI had a superior predictive capability compared to traditional obesity indices, with an area under the curve (AUC) of 0.637 (95% CI, 0.628-0.645, all P < 0.001). Mediation analysis further indicated that 14% of the association between BRI and sleep disorders was mediated by depression (P < 0.001).

CONCLUSION

Elevated BRI levels were linked to a higher prevalence of sleep disorders, with depression acting as a partial mediator in this relationship. These findings emphasize the potential connection between obesity, depression, and sleep disorders, highlighting the importance of managing visceral fat to mitigate the risk of sleep disorders.

CLINICAL TRIAL NUMBER

Not applicable.

A longitudinal study of the mediator role of physical activity in the bidirectional relationships of cognitive function and specific dimensions of depressive symptoms

BACKGROUND

The bidirectional relationship between cognitive function and depressive symptoms has been extensively reported. However, the potential mechanisms are still not clear. We aim to longitudinally investigate whether physical activity mediates the bidirectional relationships between cognitive function and specific dimensions of depressive symptoms.

METHODS

Data from 6,787 individuals aged ≥50 of 2014/15 (T1), 2016/17 (T2), and 2018/19 (T3) waves of the English Longitudinal Study of Ageing (ELSA). Cognitive function was assessed by domains of memory, orientation in time, and executive function. Physical activity was measured with the intensity and frequency of participation. Specific dimensions of depressive symptoms were assessed by the 8-item Center for Epidemiologic Studies Depression Scale, distinguishing between cognitive-affective and somatic symptoms. Cross-lagged panel models were used to investigate the mediating role of physical activity in the bidirectional relationships between cognitive function and two dimensions of depressive symptoms.

RESULTS

Poorer cognitive function was indirectly associated with worse cognitive-affective symptoms (indirect effect = -0.002, 95%CI: -0.004, -0.001) through lower physical activity levels. Poorer cognitive function was also indirectly associated with worse somatic symptoms (indirect effect = -0.003, 95%CI: -0.006, -0.002) through lower physical activity levels, and the reverse mediation was observed as well (indirect effect = -0.002, 95%CI: -0.004, -0.001).

LIMITATIONS

There is no distinction between potential within-person and between-person effects.

CONCLUSIONS

Collaborative interventions of physical activity are beneficial in protecting cognitive function and mental health in older adults.

The relationship between BMI and depression: a cross-sectional study

Introduction

Mental health problems, especially depressive symptoms, are becoming increasingly prominent, posing a significant risk to public health. Changes in the body mass index (BMI) may impact an individual's mental health, however, the relationship between BMI and depressive symptoms is unclear. The purpose of this study was to investigate the association between BMI and depressive symptoms.

Methods

Using a multi-stage sampling method, 10,686 adults in Longgang District, Shenzhen City, Guangdong Province, China, were selected for participation in this study. Surveys were distributed in 2020 and 2021 to measure participant demographic data and health. Binary logistic regression, restricted cubic spline regression, and subgroup analyses were performed to explore the relationship between BMI and depressive symptoms.

Results

The results showed a U-shaped relationship between BMI and depression. Both obesity and underweight increased the risk of depression among the participants, especially in subgroups of participants who were young, highly educated, single and employed.

Conclusion

These findings suggest that adults should try to maintain a normal body weight as a way to prevent depression and maintain their physical and mental health.

Eight-year total, cognitive-affective, and somatic depressive symptoms trajectories and risks of cardiac events

In this study, we analyzed pooled data from two prospective population-based cohorts-the Health Retirement Study (HRS) and the English Longitudinal Study of Ageing (ELSA)-to explore the association between trajectories of depressive symptoms and the risk of cardiac events. Depressive symptoms were assessed using the 8-item CES-D scale and categorized into somatic and cognitive-affective subtypes. Trajectories were tracked for four surveys from baseline. Heart disease was identified based on self-reported physician-diagnosed conditions. Hazard ratios and 95% confidence intervals were calculated with Cox proportional risk models that adjusted for potential confounders. In total, 17,787 subjects (59.7% female, median age 63 years) were enrolled at baseline. During a 10-year follow-up, 2409 cases of heart disease were identified. Participants with fluctuating (HR = 1.13, 95% CI: 1.06-1.20), increasing (HR = 1.43, 95% CI: 1.25-1.64), and consistently high (HR = 1.64, 95% CI: 1.45-1.84) depressive symptom trajectories exhibited an increased risk of heart disease compared to those with consistently low depressive symptoms, while a decreasing (HR = 1.07, 95% CI: 0.96-1.19) depressive symptom trajectory did not significantly affect the risk of heart disease. Moreover, the association between heart disease and somatic depressive symptoms was found to be stronger than with cognitive-affective symptoms. These findings suggest a significant link between depressive symptom trajectories and heart disease, with particular emphasis on stronger associations with somatic symptoms. It is recommended that the identification and management of depressive symptoms be incorporated into heart disease prevention strategies.

Maternal pre-pregnancy diet and prenatal depression: the mediating role of pre-pregnancy weight status and prenatal inflammation

Depression is a common prenatal psychological complication. We aimed to investigate if maternal pre-pregnancy diet can impact prenatal depressive symptoms and the mediating role of pre-pregnancy BMI and inflammation. We used data (N 1141) from the Alberta Pregnancy Outcomes and Nutrition cohort study. We calculated Mediterranean diet adherence (MED) and dietary inflammatory index (DII) scores using data from pre-pregnancy FFQ. In the third-trimester, we assessed depressive symptoms using Edinburgh Postpartum Depression Scale (EPDS) and inflammation through serum C-reactive protein (CRP) levels. BMI was calculated from self-reported pre-pregnancy weight. Race-stratified analyses (white and people of colour) were run. We observed no association between MED or DII tertiles and depressive symptoms. However, white participants in the MED tertile-3 had lower risk of depression (EPDS < 10) compared with tertile-1 (OR = 0·56, 95 % CI, 0·33, 0·95). White individuals in MED tertile-3 had lower BMI (MD = -1·08; 95 % CI, -1·77, -0·39) and CRP (MD = -0·53; 95 % CI, -0·95, -0·11) than tertile-1, and those in DII tertile-2 (MD = 0·44; 95 % CI, 0·03, 0·84) and tertile-3 (MD = 0·42; 95 % CI, 0·01, 0·83) had higher CRP than tertile-1. Among people of colour, neither MED nor DII was associated with BMI or CRP, but BMI was negatively associated with depressive symptoms (β = -0·25, 95 % CI, -0·43, -0·06). We found no association between diet and depressive symptoms through BMI or CRP, in either race. Pre-pregnancy diet might affect the risk of prenatal depression in a race-specific way. Further research is required to explore the racial differences in the association between maternal diet and prenatal depressive symptoms/depression risk.

The association between depressive symptoms and high-sensitivity C-reactive protein: Is body mass index a moderator?

Objective

Depression and obesity are highly comorbid conditions with shared biological mechanisms. It remains unclear how depressive symptoms and body mass index (BMI) interact in relation to inflammation. This cross-sectional study investigated the independent associations of depressive symptoms and BMI with high sensitivity C-reactive protein (hs-CRP), as well as the moderating role of BMI on the depressive symptoms-hs-CRP association.

Methods

Participants (n = 8827) from the 2015-2018 National Health and Nutrition Examination Surveys were aged ≥20 with a BMI ≥18.5 kg/m2, completed the Depression Screener, and had hs-CRP data. Multivariable linear regression was used to analyze hs-CRP in relation to depressive symptoms and BMI. An interaction term was included to examine whether the depressive symptoms-hs-CRP relationship differs depending on BMI.

Results

There was a slight, albeit non-significant, increase in hs-CRP levels with each one-point increase in depressive symptoms (aCoef.Estm. = 0.01, 95% CI = -0.05, 0.06, p = 0.754). Participants with overweight (aCoef.Estm. = 1.07, 95% CI = 0.61, 1.53, p < 0.001) or obese (aCoef.Estm. = 3.51, 95% CI = 3.04, 3.98, p < 0.001) BMIs had higher mean hs-CRP levels than those with a healthy BMI. There were no significant interactions between depressive symptoms and overweight (aCoef.Estm. = 0.04, 95% CI = -0.04, 0.13, p = 0.278) or obese (aCoef.Estm. = 0.11, 95% CI = -0.01, 0.22, p = 0.066) BMI indicating a lack of difference in the depressive symptoms-hs-CRP association across participants in the healthy versus overweight and obese ranges.

Conclusions

This study suggests that BMI might not act as a moderator in the association between depressive symptoms and hs-CRP. Results should be replicated in larger samples. Further research is warranted to understand underlying mechanisms.

Early life stress in relation with risk of overweight, depression, and their comorbidity across adulthood: findings from a British birth cohort

BACKGROUND

Multimorbidity, known as the co-occurrence of at least two chronic conditions, has become of increasing concern in the current context of ageing populations, though it affects all ages. Early life risk factors of multimorbidity include adverse childhood experiences (ACEs), particularly associated with psychological conditions and weight problems. Few studies have considered related mechanisms and focus on old age participants. We are interested in estimating, from young adulthood, the risk of overweight-depression comorbidity related to ACEs while adjusting for early life confounders and intermediate variables.

METHODS

We used data from the 1958 National Child Development Study, a prospective birth cohort study (N = 18 558). A four-category outcome (no condition, overweight only, depression only and, overweight-depression comorbidity) was constructed at 23, 33, and 42 years. Multinomial logistic regression models adjusting for intermediate variables co-occurring with this outcome were created. ACEs and sex interaction on comorbidity risk was tested.

RESULTS

In our study sample (N = 7762), we found that ACEs were associated with overweight-depression comorbidity risk throughout adulthood (RRR [95% CI] at 23y = 3.80 [2.10-6.88]) though less overtime. Comorbidity risk was larger than risk of separate conditions. Intermediate variables explained part of the association. After full-adjustment, an association remained (RRR [95% CI] at 23y = 2.00 [1.08-3.72]). Comorbidity risk related to ACEs differed by sex at 42.

CONCLUSION

Our study provides evidence on the link and potential mechanisms between ACEs and the co-occurrence of mental and physical diseases throughout the life-course. We suggest addressing ACEs in intervention strategies and public policies to go beyond single disease prevention.

Comparison of the associations between Life's Essential 8 and Life's Simple 7 with depression, as well as the mediating role of oxidative stress factors and inflammation: NHANES 2005-2018

BACKGROUND

Cardiovascular health (CVH) is closely associated with depression. However, Life's Essential 8 (LE8), a novel CVH measure, has not yet been clearly linked to depression. This study aims to explore the association between LE8 and depression, compare its advantages over Life's Simple 7 (LS7), and investigate the mediating effects of oxidative stress and inflammation.

METHODS

This study investigated cross-sectional data of adults aged 20 and above from National Health and Nutrition Examination Survey (NHANES) 2005 to 2018. The LE8 score (ranging from 0 to 100) was derived from the American Heart Association's definition, based on the unweighted average of 8 metrics, classified as low cardiovascular health (CVH) (0-49), moderate CVH (50-79), and high CVH (80-100). Similar to LE8, LS7 scores were categorized into inadequate (0-7), average (8-10), or optimal (11-14) after calculating the unweighted mean of each component. Depression was diagnosed using the Patient Health Questionnaire (PHQ-9), with a score of ≥10 defining depression. Adjusted for sociodemographic factors and other risk factors for depression, weighted logistic regression and restricted cubic spline analysis were used to explore the correlation. Receiver operating characteristic (ROC) curves were used to study the associations between CVH scores and depression. Subsequently, subgroup analysis and sensitivity analysis were conducted, followed by an exploration of the mechanisms involved.

RESULTS

A total of 7 cycles from 2005 to 2018 contained complete data. Weighted logistic regression showed that both LS7 and LE8 were significantly associated with depression. Specifically, for LE8, after adjustment, the risk of depression decreased by 52 % for moderate CVH compared to low CVH (OR: 0.48, 95 % CI: 0.41-0.57, P < 0.0001), while the risk decreased by 80 % for high CVH (OR: 0.20, 95 % CI: 0.15-0.26, P < 0.0001, Ptrend < 0.0001). For LS7, after adjustment, compared with inadequate CVH, the risk of depression decreased by 49 % for average CVH (OR: 0.51, 95 % CI: 0.34-0.78, P = 0.002), and by 55 % for optimal CVH (OR: 0.45, 95 % CI: 0.27-0.74, P = 0.002, Ptrend < 0.0001). Area under ROC curves for predicting depression were 0.672 (95 % CI, 0.66-0.684; P < 0.001) and 0.605 (95 % CI, 0.59-0.619; P < 0.001) for LE8 and LS7 (PDeLong < 0.001), respectively. Sensitivity analysis demonstrated the robustness of the association. GGT and WBC jointly mediated 9.62 % of this association (all P < 0.001).

LIMITATIONS

The cross-sectional study cannot infer causality.

CONCLUSIONS

The association between Life's Essential 8 and depression was stronger and more practical. Oxidative stress and inflammation mediate this association. Individuals with extremely poor cardiovascular health have a 7-fold increased risk of depression, highlighting the necessity of maintaining at least moderate cardiovascular health.

Association between social isolation and depression: Evidence from longitudinal and Mendelian randomization analyses

BACKGROUND

Increasing evidence shows that social isolation and depression are likely to interact with each other, yet the direction and causality of the association are not clear. This study aims to examine the possible reciprocity in the relationship between social isolation and depression.

METHODS

This study fitted a cross-lagged panel model (CLPM) by using data from the English Longitudinal Study of Aging (ELSA, 2014-2019, n = 6787) to examine the temporal relationship between social isolation and depressive symptoms in older adults. We then conducted two-sample bidirectional Mendelian randomization (MR) analyses by using independent genetic variants associated with multiple social isolation phenotypes (n = 448,858-487,647) and with depression (n = 215,644-2,113,907) as genetic instruments from genome-wide association studies to assess the causality between social isolation and onset of depression.

RESULTS

The CLPM in the ELSA cohort showed a significant and positive lagged effect of social isolation on depressive symptoms (β = 0.037, P < .001). The reverse cross-lagged path from depressive symptoms to social isolation was also statistically significant (β = 0.039, P < .001). In two-sample bidirectional MR, the genetically predicted loneliness and social isolation combined phenotype (LNL-ISO) was positively associated with occurrence of depression (OR = 1.88, 95 % CI: 1.41-2.50, P < .001), vice versa (OR = 1.16, 95 % CI:1.13-1.20, P < .001).

LIMITATIONS

The self-report nature of the assessments and missing data are study limitations.

CONCLUSIONS

These findings suggest a bidirectional relationship between social isolation and depression. It is important to develop interventions that highlight the reciprocal consequences of improving either mental health or social connection in older adults.

The potential causal relationship between various lifestyles and depression: a univariable and multivariable Mendelian randomization study

Background

Previous studies have shown that lifestyle was associated with depression. Thus, the aim of this study was to examine the causality between multiple lifestyles and depression by Mendelian randomization (MR) analysis.

Methods

The single-nucleotide polymorphisms (SNPs) of depression, alcoholic drinks per week, sleeplessness or insomnia, body mass index (BMI), mood swings, weekly usage of mobile phone in the last 3 months, beef intake, cooked vegetable intake, and "smoking status: never" were acquired from the Integrative Epidemiology Unit Open genome-wide association study database. Causal effects of eight exposure factors and depression were investigated using MR-Egger, weighted median, inverse variance weighted (IVW), simple mode, and weighted mode, and results were primarily referred to IVW. Subsequently, univariable MR (UVMR) analysis was performed on eight exposure factors and depression, separately. In addition, sensitivity analysis, including heterogeneity test, horizontal pleiotropy, and leave-one-out (LOO) methods, was conducted to evaluate the stability of MR results. Furthermore, multivariable MR (MVMR) analysis was carried out.

Results

UVMR analysis revealed that all eight exposure factors were causally associated with depression; alcoholic drinks per week, sleeplessness or insomnia, BMI, mood swings, weekly usage of mobile phone in the last 3 months, and cooked vegetable intake were risk factors, and beef intake and "smoking status: never" were protection factors. Heterogeneity tests revealed no heterogeneity for alcoholic drinks per week, sleeplessness or insomnia, mood swings, weekly usage of mobile phone in the last 3 months, and cooked vegetable intake. Meanwhile, there was no horizontal pleiotropy in UVMR, and LOO analysis verified that univariable analysis results were reliable. Moreover, MVMR analysis indicated that mood swings and weekly usage of mobile phone in the last 3 months were risk factors, and beef intake was a protection factor for depression when multiple factors occurred at the same time.

Conclusion

Alcoholic drinks per week, sleeplessness or insomnia, BMI, mood swings, weekly usage of mobile phone in the last 3 months, and cooked vegetable intake were risk factors, and beef intake and "smoking status: never" were protection factors. In addition, mood swings, weekly usage of mobile phone in the last 3 months, and beef intake had a direct effect on depression when multiple factors occurred simultaneously.

Associations between metabolic syndrome and anxiety, and the mediating role of inflammation: Findings from the UK Biobank

OBJECTIVES

To investigate the association between metabolic syndrome (MetS) and anxiety and to explore the mediating role of inflammation indicators in this relationship based on the UK Biobank prospective cohort.

METHODS

This population-based retrospective cohort study analyzed data from 308,352 participants. MetS was defined according to criteria jointly developed by the American Heart Association, the National Heart, Lung, and Blood Institute, and the International Diabetes Federation. Anxiety was defined using ICD-10 codes. Cox proportional risk regression models were used to explore the hazard ratios (HRs) between MetS, components of MetS, number of MetS components, and anxiety. The mediating effect of inflammation on the association between MetS and anxiety was explored using longitudinal mediation analysis.

RESULTS

A total of 308,352 participants were included in this study. Of these, 9471 (3.071 %) developed anxiety over a mean follow-up of 12.05 years. In the fully adjusted model, MetS increased the risk of anxiety by 13.6 % (HR: 1.136, 95 %CI: 1.085-1.189). All MetS components significantly increased the risk of anxiety, with HRs ranging from 1.066 to 1.165. When MetS was treated as a linear variable, the risk of anxiety increased by 6.5 % per component increment. Age-stratified results showed that the risk of MetS for anxiety was higher among those <55 years (HR: 1.23, 95 %CI: 1.13-1.33) than among those ≥55 years (HR: 1.12, 95 %CI: 1.06-1.18). The mediating effects of platelets, lymphocytes, neutrophils, C-reactive protein, leukocytes, and INFLA scores on the association between MetS and anxiety were significant, with mediating effects of 2.30 %, 7.20 %, 15.9 %, 20.7 %, 22.0 %, and 25.3 %, respectively, and a combined mediating effect of these inflammatory factors was 30.8 % (except for INFLA scores).

CONCLUSIONS

MetS and its components significantly increased the risk of anxiety, which increased with the number of components. This association may be partially mediated by serum inflammatory indicators, suggesting that MetS may increase the risk of anxiety by elevating the level of chronic inflammation.

Obesity and psychological distress

The relationship between high body weight and mental health has been studied for several decades. Improvements in the quality of epidemiological, mechanistic and psychological research have brought greater consistency to our understanding of the links. Large-scale population-based epidemiological research has established that high body weight is associated with poorer mental health, particularly depression and subclinical depressive symptoms. There is some evidence for bidirectional relationships, but the most convincing findings are that greater body weight leads to psychological distress rather than the reverse. Particular symptoms of depression and distress may be specifically related to greater body weight. The psychological stress induced by weight stigma and discrimination contributes to psychological distress, and may in turn handicap efforts at weight control. Heightened systemic inflammation and dysregulation of the hypothalamic-pituitary-adrenal axis are biological mechanisms that mediate in part the relationship of greater body weight with poorer mental health. Changing negative societal attitudes to high body weights would improve the wellbeing of people living with obesity, and promote more effective weight-inclusive attitudes and behaviours in society at large, particularly in healthcare settings. This article is part of a discussion meeting issue 'Causes of obesity: theories, conjectures and evidence (Part II)'.

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.

Shared biological mechanisms of depression and obesity: focus on adipokines and lipokines

Depression and obesity are both common disorders currently affecting public health, frequently occurring simultaneously within individuals, and the relationship between these disorders is bidirectional. The association between obesity and depression is highly co-morbid and tends to significantly exacerbate metabolic and related depressive symptoms. However, the neural mechanism under the mutual control of obesity and depression is largely inscrutable. This review focuses particularly on alterations in systems that may mechanistically explain the in vivo homeostatic regulation of the obesity and depression link, such as immune-inflammatory activation, gut microbiota, neuroplasticity, HPA axis dysregulation as well as neuroendocrine regulators of energy metabolism including adipocytokines and lipokines. In addition, the review summarizes potential and future treatments for obesity and depression and raises several questions that need to be answered in future research. This review will provide a comprehensive description and localization of the biological connection between obesity and depression to better understand the co-morbidity of obesity and depression.

Personalized Medicine of Omega-3 Fatty Acids in Depression Treatment in Obese and Metabolically Dysregulated Patients

The co-occurrence of depression and obesity has become a significant public health concern worldwide. Recent studies have shown that metabolic dysfunction, which is commonly observed in obese individuals and is characterized by inflammation, insulin resistance, leptin resistance, and hypertension, is a critical risk factor for depression. This dysfunction may induce structural and functional changes in the brain, ultimately contributing to depression's development. Given that obesity and depression mutually increase each other's risk of development by 50-60%, there is a need for effective interventions that address both conditions. The comorbidity of depression with obesity and metabolic dysregulation is thought to be related to chronic low-grade inflammation, characterized by increased circulating levels of pro-inflammatory cytokines and C-reactive protein (CRP). As pharmacotherapy fails in at least 30-40% of cases to adequately treat major depressive disorder, a nutritional approach is emerging as a promising alternative. Omega-3 polyunsaturated fatty acids (n-3 PUFAs) are a promising dietary intervention that can reduce inflammatory biomarkers, particularly in patients with high levels of inflammation, including pregnant women with gestational diabetes, patients with type 2 diabetes mellitus, and overweight individuals with major depressive disorder. Further efforts directed at implementing these strategies in clinical practice could contribute to improved outcomes in patients with depression, comorbid obesity, and/or metabolic dysregulation.