Using the Avon Longitudinal Study of Parents and Children birth cohort, we used regression analyses to examine: (1) cross-sectional and (2) longitudinal associations between measures of DGIH [insulin resistance (IR); impaired glucose tolerance] and body mass index (BMI) at ages 9 and 18 years, and depression (depressive symptoms and depressive episode) at age 18 years and (3) whether sociodemographics, lifestyle factors or inflammation [interleukin-6 (IL-6) at age 9 years] confounded any such associations.
We found that increased plasma IL-6 and IL-8 and reductions of serotonin, IL-2 and quinolinic acid were associated with the severity of depressive symptoms and increased the risk for PPD.
IL-6 partially mediated the association between increasing exposure to events over time in childhood and depressive symptoms at the beginning of adolescence.
Among all patients, in a multiple regression analysis predicting presence of somatic/affective depressive symptoms, sST2 (P = .026), IL-6 (P = .010), B-type natriuretic peptide (P = .016), and sleep (Pittsburgh Sleep Quality Index [P < .001]) were significant predictors (overall model F = 15.39, P < .001, adjusted R<sup>2</sup> = .207).
For T2D, hsCRP, IL-1RA, CCL2 and adiponectin or its isoforms were associated with depressive symptoms in at least two studies, whereas positive associations of IL-1β, IL-6 and IL-18 with depressive symptoms or depression were reported from single cohorts.
After controlling for demographic characteristics, body mass index, and depressive symptoms, attachment avoidance and anxiety were associated with IL-6 but not CRP.
Using longitudinal data, we have tested whether childhood serum interleukin 6 (IL-6) and C-reactive protein (CRP) levels are associated with specific depressive symptoms in early adulthood.
Pro-inflammatory markers interleukin-6 and tumor necrosis factor-α were associated with longer sleep duration and fewer depressive symptoms, respectively.
Anti-IL-6 antibodies (SMD = 0.8, 95% CI [0.20-1.41]) and an anti-IL-12/23 antibody (SMD = 0.48, 95% CI [0.26-0.70]) had larger effects on depressive symptoms than other drug classes.
While cross-sectional associations of inflammatory markers interleukin-6 (IL-6) and C-reactive protein with major depressive disorder are well established, evidence for longitudinal associations mostly comes from studies on depression symptoms, not diagnoses.
Baseline TNF (beta = 0.361, p = 0.007) and IL-6 (beta = -0.306, p = 0.026) predicted negative symptoms slopes, along with depressive symptom severity at baseline (beta = -0.596, p = 0.000).
To provide more evidence, we measured the plasma levels of IL-1β, IL-6, interferon (INT)-α2, INT-γ, and tumor necrosis factor (TNF)-α in patients having MDD and explored correlations between the five proinflammatory cytokines and specific depressive symptoms.
More frequent stressful life events before BD1 predicted significantly more severe depressive symptoms at BD2, but only for adolescents with moderate (50th percentile) and high (84th percentile) levels of IL-6 and CRP at BD2.
Monoclonal antibodies against proinflammatory cytokines, such as interleukin 6, interleukin 17, and tumor necrosis factor α, have demonstrated antidepressant effects in patients with chronic inflammatory conditions who report significant depressive symptoms.
In patients with T2D, reductions in depressive symptoms were associated with reductions in high-sensitivity C-reactive protein (hsCRP), interleukin (IL)-18 and IL-1 receptor antagonist (IL-1RA) (P ≤ 0.016), whereas no associations were seen for IL-6, CCL2 and adiponectin.
Depression was directly related to evening salivary cortisol and inflammation, such that higher evening cortisol predicted greater depressive symptoms (β=0.215, p<0.01) and higher pro-inflammatory cytokines (interleukin-2 [IL-2], IL-6, and tumor necrosis factor-alpha [TNF-α] levels (β=0.185, p<0.05), when controlling for covariates.
Studies including a complete evaluation of inflammatory markers are scarce and high levels of interleukin-6 (IL-6) and C-reactive protein (CRP) are the most consistent findings associated with obesity and symptoms of depression.