Increased soluble interleukin-2 receptor levels are related to somatic but not to cognitive-affective features in major depression

Meta-analysis of soluble tumour necrosis factor receptors in severe mental illnesses

Tumour necrosis factor (TNF), as an innate immune defense molecule, functions through binding to TNF receptor 1 (TNFR1) or TNF receptor 2 (TNFR2). Peripheral levels of soluble TNFR1 (sTNFR1) and soluble TNFR2 (sTNFR2) were widely measured in severe mental illnesses (SMIs) including schizophrenia (SCZ), bipolar disorder (BD) and major depressive disorder (MDD) but inconsistencies existed. Hence, the present meta-analysis was conducted to identify the overall association between plasma/serum sTNFR1 and sTNFR2 levels and SMIs. Published studies were searched using Pubmed and Scopus. Data were analysed using Comprehensive Meta-Analysis version 2. Hedges's g effect sizes and 95% confidence intervals were pooled using fixed-effect or random-effects models. Heterogeneity, publication bias and study quality were assessed. Sensitivity analysis and subgroup analysis were performed. Our findings revealed that sTNFR1 level was significantly higher in SMI, particularly in BD. The sTNFR2 level significantly elevated in SMI but with smaller effect size. These findings further support the association between altered immune system and inflammatory abnormalities in SMI, especially in patients with BD. Subgroup analysis showed that younger age of onset, longer illness duration and psychotropic medication raised both sTNFR levels, especially sTNFR1, as these factors may contribute to the activation of inflammation. Future studies were suggested to identify the causality between TNFR pathway and SCZ, BD and MDD respectively using homogenous group of each SMI, and to determine the longitudinal effect of each psychotropic medication on TNFR pathway.

Selected Biomarkers of Depression: What Are the Effects of Cytokines and Inflammation?

Depression is one of the leading mental illnesses worldwide and lowers the quality of life of many. According to WHO, about 5% of the worldwide population suffers from depression. Newer studies report a staggering global prevalence of 27.6%, and it is rising. Professionally, depression belonging to affective disorders is a psychiatric illness, and the category of major depressive disorder (MDD) comprises various diagnoses related to persistent and disruptive mood disorders. Due to this fact, it is imperative to find a way to assess depression quantitatively using a specific biomarker or a panel of biomarkers that would be able to reflect the patients' state and the effects of therapy. Cytokines, hormones, oxidative stress markers, and neuropeptides are studied in association with depression. The latest research into inflammatory cytokines shows that their relationship with the etiology of depression is causative. There are stronger cytokine reactions to pathogens and stressors in depression. If combined with other predisposing factors, responses lead to prolonged inflammatory processes, prolonged dysregulation of various axes, stress, pain, mood changes, anxiety, and depression. This review focuses on the most recent data on cytokines as markers of depression concerning their roles in its pathogenesis, their possible use in diagnosis and management, their different levels in bodily fluids, and their similarities in animal studies. However, cytokines are not isolated from the pathophysiologic mechanisms of depression or other psychiatric disorders. Their effects are only a part of the whole pathway.

Inflammatory Cytokines, but Not Dietary Patterns, Are Related to Somatic Symptoms of Depression in a Sample of Women

Background

Depression is a heterogenous disorder with both cognitive and somatic symptom dimensions that may differentially relate to systemic inflammation. Diet, which has the potential to modulate both inflammation levels and mood, is yet to be studied within the context of individual depression dimensions. This study examined the associations between inflammatory cytokines and dietary patterns with depressive symptom dimension profiles among a sample of women recruited in a non-clinical setting.

Methods

Inflammatory cytokines (IL-6 and TNF-α), inflammatory diet (Diet Inflammatory Index; DII), and depressive symptoms (Beck Depression Inventory-II; BDI-II) were measured in 136 females (M age = 22.01 ± 4.02, range 18-59 years). Multiple linear regressions were used to investigate the relationships between inflammatory cytokines and diet with self-reported cognitive, somatic, and total depressive symptoms, adjusting for demographic factors.

Results

Findings showed that increased somatic dimension scores were positively associated with IL-6 (ß = 0.273, p = 0.002) and TNF-α (ß = 0.215, p = 0.017), but not inflammatory diet (p = 0.300). Total BDI-II scores were only positively associated with IL-6 (ß = 0.221, p = 0.012), and cognitive dimension scores were not associated with any inflammation measures.

Conclusions

These findings contribute to existing evidence that inflammatory cytokines are associated with the somatic symptoms of depression. Inflammatory diet index was not associated with depression measures.

Body Mass Index and Somatic Symptom Severity in Patients with Somatic Symptom Disorder: The Mediating Role of Working Memory

Objective

In somatic symptom disorder (SSD), cognitive dysfunction is related to perceptive distortion that excessively amplifies bodily sensations. The association between high body mass index (BMI) and cognitive dysfunction could be attributed to underlying systemic inflammation. We aimed to evaluate whether patients with SSD and high BMI exhibit increased somatic symptom severity and whether this is mediated by cognitive dysfunction.

Methods

This retrospective, cross-sectional study was conducted on 54 patients with SSD (20 males/34 females, mean age ± standard deviation 40.65 ± 13.23 years). Participants’ BMI, laboratory data including complete blood count and lipid profile, results from the Korean Wechsler Adult Intelligence Scale-IV, and scores of the Korean-Symptom Checklist 95-Somatization (SCL95-SOM) were analyzed. We performed a path analysis to evaluate BMI as a predictor of somatic symptoms.

Results

In a path analysis, the SCL95-SOM score was directly influenced by working memory (b = −0.326, p = 0.032), which was significantly influenced by BMI (b = −0.338, p = 0.009), although there was no direct effect of BMI on the SCL95-SOM score. The path analytic model showed a close fit to the data with the following values c² (df) = 0.918 (1), p = 0.338, root mean square error of approximation = 0.000 (< 0.001), and comparative fit index = 1.00.

Conclusion

Patients with SSD and high BMI may exhibit increased somatic symptom severity, and this is mediated by working memory dysfunction. Weight management may help improve symptoms in patients with SSD and high BMI.

Inflammatory markers in depression: A meta-analysis of mean differences and variability in 5,166 patients and 5,083 controls

IMPORTANCE

The magnitude and variability of cytokine alterations in depression are not clear.

OBJECTIVE

To perform an up to date meta-analysis of mean differences of immune markers in depression, and to quantify and test for evidence of heterogeneity in immune markers in depression by conducting a meta-analysis of variability to ascertain whether only a sub-group of patients with depression show evidence of inflammation.

DATA SOURCES

Studies that reported immune marker levels in peripheral blood in patients with depression and matched healthy controls in the MEDLINE database from inception to August 29th 2018 were examined.

STUDY SELECTION

Case-control studies that reported immune marker levels in peripheral blood in patients with depression and healthy controls were selected.

DATA EXTRACTION AND SYNTHESIS

Means and variances (SDs) were extracted for each measure to calculate effect sizes, which were combined using multivariate meta-analysis.

MAIN OUTCOMES AND MEASURES

Hedges g was used to quantify mean differences. Relative variability of immune marker measurements in patients compared with control groups as indexed by the coefficient of variation ratio (CVR).

RESULTS

A total of 107 studies that reported measurements from 5,166 patients with depression and 5,083 controls were included in the analyses. Levels of CRP (g = 0.71; 95%CI: 0.50-0.92; p < 0.0001); IL-3 (g = 0.60; 95%CI: 0.31-0.89; p < 0.0001); IL-6 (g = 0.61; 95%CI: 0.39-0.82; p < 0.0001); IL-12 (g = 1.18; 95%CI: 0.74-1.62; p < 0.0001); IL-18 (g = 1.97; 95%CI: 1.00-2.95; p < 0.0001); sIL-2R (g = 0.71; 95%CI: 0.44-0.98; p < 0.0001); and TNFα (g = 0.54; 95%CI: 0.32-0.76; p < 0.0001) were significantly higher in patients with depression. These findings were robust to a range of potential confounds and moderators. Mean-scaled variability, measured as CVR, was significantly lower in patients with depression for CRP (CVR = 0.85; 95%CI: 0.75-0.98; p = 0.02); IL-12 (CVR = 0.61; 95%CI: 0.46-0.80; p < 0.01); and sIL-2R (CVR = 0.85; 95%CI: 0.73-0.99; p = 0.04), while it was unchanged for IL-3, IL-6, IL-18, and TNF α.

CONCLUSIONS AND RELEVANCE

Depression is confirmed as a pro-inflammatory state. Some of the inflammatory markers elevated in depression, including CRP and IL-12, show reduced variability in patients with depression, therefore supporting greater homogeneity in terms of an inflammatory phenotype in depression. Some inflammatory marker elevations in depression do not appear due to an inflamed sub-group, but rather to a right shift of the immune marker distribution.

Inflammation and the dimensions of depression: A review

Patients with depressive disorders show a wide range of clinical manifestations including cognitive and neurovegetative symptoms. Importantly, these symptoms can differ in terms of biological etiology, and deconstructing depression into specific symptoms may provide valuable insight into the underlying neurobiology. Little research has examined inflammation in the context of depressive dimensions. Here we conduct a narrative review of the existing literature (21 studies) to elucidate whether the depression-inflammation link is symptom specific. Overall, there is evidence that an association exists between neurovegetative symptoms of depression and inflammation, independent of cognitive symptoms. The same cannot be said of cognitive symptoms and inflammation. There is also some evidence of gender differences in the directionality of the relationship between depression and inflammation. Potential explanations for these findings, limitations of the existing literature and recommendations for future research design are discussed.

Shared microglial mechanisms underpinning depression and chronic fatigue syndrome and their comorbidities

In 2011, it was reviewed that a) there is a strong co-occurrence between major depression and chronic fatigue syndrome (CFS), with fatigue and physio-somatic symptoms being key symptoms of depression, and depressive symptoms appearing during the course of CFS; and b) the comorbidity between both disorders may in part be explained by activated immune-inflammatory pathways, including increased translocation of Gram-negative bacteria and increased levels of pro-inflammatory cytokines, such as interleukin (IL)-1. Nevertheless, the possible involvement of activated microglia in this comorbidity has remained unclear. This paper aims to review microglial disturbances in major depression, CFS and their comorbidity. A comprehensive literature search was conducted using the PubMed / MEDLINE database to identify studies, which are relevant to this current review. Depressed patients present neuroinflammatory alterations, probably related to microglial activation, while animal models show that a microglial response to immune challenges including lipopolysaccharides is accompanied by depressive-like behaviors. Recent evidence from preclinical studies indicates that activated microglia have a key role in the onset of fatigue. In chronic inflammatory conditions, such as infections and senescence, microglia orchestrate an inflammatory microenvironment thereby causing fatigue. In conclusion, based on our review we may posit that shared immune-inflammatory pathways and especially activated microglia underpin comorbid depression and CFS. As such, microglial activation and neuro-inflammation may be promising targets to treat the overlapping manifestations of both depression and CFS.

Cytokine alterations and cognitive impairment in major depressive disorder: From putative mechanisms to novel treatment targets

Overwhelming evidence indicates the involvement of immune-inflammatory processes in the pathophysiology of major depressive disorder (MDD). Peripheral cytokine alterations serve as one of most consistently reported indices of subthreshold inflammatory state observed in MDD. Although cytokines cannot pass directly through the blood-brain barrier, a number of transport mechanisms have been reported. In addition, peripheral cytokines may impact central nervous system via downstream effectors of their biological activity. Animal model studies have provided evidence that cytokines might impact cognitive performance through direct and indirect effects on long-term potentiation, neurogenesis and synaptic plasticity. Therefore, it has been hypothesized that cytokine alterations might contribute to cognitive impairment that is widely observed in MDD and persists beyond episodes of acute relapse in the majority of patients. Although several studies have provided that peripheral cytokine alterations might be related to cognitive deficits in patients with MDD, the quality of evidence still leaves much to be desired due to methodological heterogeneity and limitations. In this article, we provide an overview of studies investigating the association between peripheral cytokine alterations and cognitive performance in MDD, discuss underlying mechanisms and neural substrates. Finally, we propose possible treatment targets related to cytokine alterations taking into account existing evidence for antidepressant efficacy of anti-inflammatory pharmacological treatment modalities.

Cytokines and depression in cancer patients and caregivers

OBJECTIVE

A better understanding of the biobehavioral mechanisms underlying depression in cancer is required to translate biomarker findings into clinical interventions. We tested for associations between cytokines and the somatic and psychological symptoms of depression in cancer patients and their healthy caregivers.

PATIENTS AND METHODS

The GRID Hamilton Rating Scale for Depression (Ham-D) was administered to 61 cancer patients of mixed type and stage, 26 primary caregivers and 38 healthy controls. Concurrently, blood was drawn for multiplexed plasma assays of 15 cytokines. Multiple linear regression, adjusted for biobehavioral variables, identified cytokine associations with the psychological (Ham-Dep) and somatic (Ham-Som) subfactors of the Ham-D.

RESULTS

The Ham-Dep scores of cancer patients were similar to their caregivers, but their Ham-Som scores were significantly higher (twofold, p=0.016). Ham-Som was positively associated with IL-1ra (coefficient: 1.27, p≤0.001) in cancer patients, and negatively associated with IL-2 (coefficient: -0.68, p=0.018) in caregivers. Ham-Dep was negatively associated with IL-4 (coefficient: -0.67, p=0.004) in cancer patients and negatively associated with IL-17 (coefficient: -1.81, p=0.002) in caregivers.

CONCLUSION

The differential severity of somatic symptoms of depression in cancer patients and caregivers and the unique cytokine associations identified with each group suggests the potential for targeted interventions based on phenomenology and biology. The clinical implication is that depressive symptoms in cancer patients can arise from biological stressors, which is an important message to help destigmatize the development of depression in cancer patients.

Peripheral Immune Alterations in Major Depression: The Role of Subtypes and Pathogenetic Characteristics

Depression has been associated with peripheral inflammatory processes and alterations in cellular immunity. Growing evidence suggests that immunological alterations may neither be necessary nor sufficient to induce depression in general, but seem to be associated with specific features. Using baseline data from the Outcome of Psychological Interventions in Depression trial, this exploratory study examines associations between depression subtypes and pathogenetic characteristics (i.e., melancholic vs non-melancholic depression, chronic vs non-chronic depression, age of onset, cognitive-affective and somatic symptom dimensions) with plasma levels of C-reactive protein (CRP), interleukin (IL)-6, IL-10, and numbers of leukocyte subpopulations in 98 patients with major depression (MD) and 30 age and sex-matched controls. Patients with MD exhibited higher CRP levels, higher neutrophil and monocyte counts, lower IL-10 levels, and an increased neutrophil to lymphocyte ratio (NLR) than controls. Patient with later age of onset had higher levels of two inflammatory markers (CRP, NLR) and lower cytotoxic T cell counts after adjusting for sociodemographics, lifestyle factors, and antidepressants. Furthermore, lower anti-inflammatory IL-10 levels were related to more severe somatic depressive symptoms. These results confirm and extend previous findings suggesting that increased levels of CRP are associated with a later onset of depression and demonstrate that also NLR as a subclinical inflammatory marker is related to a later onset of depression.

Serum zinc concentrations and depression in persons with Human Immunodeficiency Virus infection: The positive living with HIV (POLH) study

Low levels of serum zinc concentrations and depression are common in persons infected with Human Immunodeficiency Virus (HIV). Low levels of serum zinc concentrations may increase risk of depression in general population. However, research on the role of zinc in depression among HIV- infected person is limited. We assessed the association between serum zinc concentrations and depression in HIV-infected persons. A cross-sectional survey was conducted among 311 HIV-positive people (177 men and 134 women) aged 18-60 years residing in Kathmandu, Nepal. The atomic absorption method was used to measure serum zinc concentrations and the Beck Depression Inventory (BDI)-Ia method was used to measure depression, with cut off score 20 or higher consistent with clinically significant depression. Relationships were assessed using multiple linear and logistic regression analyses. Serum zinc concentrations were significantly inversely associated with depression in all participants and in men but not in women. Participants with the highest tertile of serum zinc concentrations had a significantly decreased risk of depression in men but not in women. Serum zinc concentrations were inversely associated with depressive symptoms scores in HIV-infected men. Further prospective studies are needed to confirm the role of zinc in depression among persons infected with HIV.

Comparison of pro-inflammatory cytokines among patients with bipolar disorder and unipolar depression and normal controls

OBJECTIVE

Research evidence has shown that bipolar disorder (BD) and unipolar depression (UD) are both related to inflammatory dysregulation, but few studies have compared the levels of cytokines between these two disorders.

METHODS

Study subjects were age- and gender-matched outpatients with BD or UD and normal controls (NC). Severities of depression and mania symptoms were assessed with the Montgomery-Åsberg Depression Rating Scale (MADRS) and the Young Mania Rating Scale (YMRS). Pro-inflammatory cytokines, including soluble interleukin-6 receptor (sIL-6R), soluble interleukin-2 receptor (sIL-2R), C-reactive protein (CRP), soluble tumor necrosis factor receptor type 1 (sTNF-R1), soluble p-selectin receptor (sP-selectin), and monocyte chemotactic protein-1 (MCP-1), were assessed in all subjects by enzyme-linked immunosorbent assays.

RESULTS

In all, 130 patients with BD, 149 patients with UD, and 130 NC were enrolled in the study; 67.6% were female and the average age was mean ± standard deviation (SD) 43.5 ± 11.8 years. The BD group had a significantly higher smoking rate, more medical comorbidity, higher body mass index (BMI), and higher levels of sIL-2R, sIL-6R, CRP, sTNF-R1, and MCP-1 (all p < 0.01) than the UD and NC groups. When the remitted patients with BD (YMRS scores ≤ 12) were compared with the patients with UD, controlling for age, MADRS score, smoking, medical comorbidity, and BMI in the regression model, the results showed that the BD group had significantly higher levels of sIL-6R (p < 0.001), CRP (p = 0.045), sTNF-R1 (p = 0.036), and MCP-1 (p = 0.001) than the UD group.

CONCLUSIONS

Higher levels of sIL-6R, CRP, sTNF-R1, and MCP-1 were noted in BD than in UD. These results may suggest a more severe inflammatory dysregulation in BD. Further studies are required to investigate whether these cytokines could be biomarkers for affective disorders.

Association of inflammatory biomarkers with depressive symptoms and cognitive decline in a community-dwelling healthy older sample: a 3-year follow-up study

BACKGROUND

The relationship between the pathophysiology of dementia and neuroinflammation is well-known. The number of reports stating that depression is a risk factor for dementia has recently been increasing. These epidemiological findings suggest the possibility that both depression and dementia have common pathophysiological backgrounds of neuroinflammation.

METHODS

The sample consists of 64 non-demented community-dwelling older participants aged 65 years or over. Participants were assessed at baseline (2004-2006) and 3 years later (2007-2009). Plasma concentration of markers of inflammation (interleukins (IL)-1β, IL-2, IL-6, soluble interleukin-2 receptor (sIL-2R), soluble interleukin-6 receptor (sIL-6R), high sensitivity C-reactive protein (hsCRP) and tumor necrosis factor (TNF)-α) were measured at baseline. Depression symptoms were assessed with the Beck Depression Inventory (BDI) and cognitive decline was assessed with the Mini-Mental State Examination (MMSE), Frontal Assessment Battery (FAB) and Clock Drawing Test (CDT) at baseline and follow-up. All analyses were adjusted for age, gender and years of education.

RESULTS

In the cross-sectional analysis, the present study found soluble IL-2 receptor (sIL-2R) to be associated only with the MMSE score at baseline in men. In the longitudinal analysis, none of our inflammatory biomarkers were associated with either depressive symptoms or cognitive decline.

LIMITATIONS

The present study consists of small number of participants and body mass index (BMI) scores were not obtained.

CONCLUSIONS

Our findings suggest that sIL-2R is associated with current cognitive function in men. None of our inflammatory markers predicted future depressive state or cognitive decline in our community-dwelling healthy older sample.

Blunted exercise-induced mobilization of monocytes in somatization syndromes and major depression

BACKGROUND

Previous research indicates that physical activity may alter the number of immune cells. We examined whether increasing or decreasing the level of physical activity affects circulating lymphocyte and monocyte counts in patients with somatization syndromes and patients with major depression.

METHODS

Thirty-eight participants with major depression, 26 participants with somatization syndromes and 47 healthy controls participated in the study. Using an experimental within-subject design, participants were involved in 1 week of increased physical activity (daily exercise sessions) and 1 week of reduced physical activity. Counts of total lymphocytes, lymphocyte subsets and monocytes were determined before and after each trial. Linear mixed models adjusted for sex, body mass index, age, fitness status and the order of trials were used for longitudinal data analysis.

RESULTS

One week of exercise increases the number of monocytes in healthy controls (p<.05), but not in patients with somatization syndromes or patients with major depression. In addition, after 1 week of exercise, depressive symptoms were reduced in patients with major depression (p<.05) while somatoform symptoms were reduced (p<.05) in both clinical groups. Baseline comparisons and mixed models indicated reduced T helper cell counts in patients with somatization syndromes.

LIMITATIONS

Relatively small sample size. The time of physical activity was relatively short and restricted to low-graded exercise.

CONCLUSIONS

This study demonstrates a blunted mobilization of monocytes by exercise in both patients with somatization syndromes and patients with major depression. In addition, even one week of exercise reduces somatoform and depressive symptoms.

Pro-inflammatory cytokine associated with somatic and pain symptoms in depression

BACKGROUND

More than two-thirds of depressed patients complain of somatic and pain symptoms, which are frequently regarded as a psychological reaction. Although there is a growing body of evidence showing that depression is related to immune abnormalities, few studies have investigated the association between inflammatory cytokines and somatic/pain symptoms.

METHOD

Patients with depressive disorder but without any medical disorders, and age/gender/body mass index (BMI)-matched healthy subjects were enrolled. All the subjects completed the self-rating scales of the Beck Depression Inventory-II and the Depression and Somatic Symptoms Scale, which was comprised of depressive, somatic, and pain subscales. Pro-inflammatory cytokines, including C-reactive protein (CRP), interleukin-2 receptor (sIL-2R), soluble interleukin 6 receptor (sIL-6R), soluble TNF-receptors (sTNF-R), soluble P-selectin (sP-selectin), monocyte chemotactic protein-1 (MCP-1), and adiponectin, were assessed by enzyme-linked immunosorbent assays.

RESULTS

In all, 109 patients with depressive disorder and 126 normal controls were enrolled. The patients with depressive disorder had significantly more severe depression, somatic and pain symptoms (all p<0.001), and higher levels of sIL-2R (p<0.0001), sTNF-R (p<0.001), and sP-selectin (p=0.005) than the normal control group. Using multivariate regression analysis with controlling of age, gender, BMI, and other pro-inflammatory cytokines, sIL-2R was the most significant predictor for depressive symptoms (p<0.0001); with further controlling of severity of depressive symptom, sP-selectin was the only predictor for somatic (p=0.002) and pain (p=0.059) symptoms.

CONCLUSION

The elevated sP-selectin associated with somatic symptoms in depression, may indicate early micro-vascular changes occur subtly, and provide neurobiological evidence for somatic and pain symptom in depression.

The predictive value of somatic and cognitive depressive symptoms for cytokine changes in patients with major depression

CONTEXT

Elevated concentrations of proinflammatory cytokines have been hypothesized as an important factor in the pathophysiology of depression. Depression itself is considered to be a heterogeneous disorder. Current findings suggest that "cognitive" and "somatic" symptom dimensions are related to immune function in different ways. So far, little research has been done on the longitudinal aspects of inflammation in patients with major depression, especially with respect to different symptom dimensions of depression. Therefore, we investigated which aspects of depression may predict changes in tumor necrosis factor-alpha (TNF-alpha) and interleukin (IL)-6 over 4 weeks.

METHODS

Forty-one patients with major depression diagnosed according to the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV), and 45 healthy controls were enrolled. Serum measurements of TNF-alpha and IL-6 were conducted at baseline and 4 weeks later. Psychometric measures included the assessment of cognitive-affective depressive symptoms and somatic symptoms during the last 7 days as well as somatic symptoms during the last 2 years.

RESULTS

Patients with depression showed increased levels of TNF-alpha (P<0.05) compared to healthy controls. Hierarchical regression analyses indicated that neither depressive nor somatic symptoms predict changes in proinflammatory cytokines in the whole sample of depressed patients. Moderation analyses and subsequent sex-stratified regression analyses indicated that higher somatoform symptoms during the last 2 years significantly predict an increase in TNF-alpha in women with major depression (P<0.05) but not in men. Exploratory analyses indicated that the stability of TNF-alpha and IL-6 (as indicated by intraclass correlation coefficients) over 4 weeks was high for TNF-alpha but lower for IL-6.

CONCLUSION

The present study demonstrated that a history of somatoform symptoms may be important for predicting future changes in TNF-alpha in women with major depression.

Zinc in depression: a meta-analysis

BACKGROUND

Zinc is an essential micronutrient with diverse biological roles in cell growth, apoptosis and metabolism, and in the regulation of endocrine, immune, and neuronal functions implicated in the pathophysiology of depression. This study sought to quantitatively summarize the clinical data comparing peripheral blood zinc concentrations between depressed and nondepressed subjects.

METHODS

PubMed, Cumulated Index to Nursing and Allied Health Literature, and PsycINFO were searched for original peer-reviewed studies (to June 2012) measuring zinc concentrations in serum or plasma from depressed subjects (identified by either screening or clinical criteria) and nondepressed control subjects. Mean (±SD) zinc concentrations were extracted, combined quantitatively in random-effects meta-analysis, and summarized as a weighted mean difference (WMD).

RESULTS

Seventeen studies, measuring peripheral blood zinc concentrations in 1643 depressed and 804 control subjects, were included. Zinc concentrations were approximately -1.85 µmol/L lower in depressed subjects than control subjects (95% confidence interval: [CI]: -2.51 to -1.19 µmol/L, Z17 = 5.45, p < .00001). Heterogeneity was detected (χ(2)17 = 142.81, p < .00001, I(2) = 88%) and explored; in studies that quantified depressive symptoms, greater depression severity was associated with greater relative zinc deficiency (B = -1.503, t9 = -2.82, p = .026). Effect sizes were numerically larger in studies of inpatients (WMD -2.543, 95% CI: -3.522 to -1.564, Z9 = 5.09, p < .0001) versus community samples (WMD -.943, 95% CI: -1.563 to -.323, Z7 = 2.98, p = .003) and in studies of higher methodological quality (WMD -2.354, 95% CI: -2.901 to -1.807, Z7 = 8.43, p < .0001).

CONCLUSIONS

Depression is associated with a lower concentration of zinc in peripheral blood. The pathophysiological relationships between zinc status and depression, and the potential benefits of zinc supplementation in depressed patients, warrant further investigation.