Prevalence of low-grade inflammation in depression: a systematic review and meta-analysis of CRP levels

Psychol Med. 2019 Sep;49(12):1958-1970. doi: 10.1017/S0033291719001454. Epub 2019 Jul 1.


Background: Peripheral low-grade inflammation in depression is increasingly seen as a therapeutic target. We aimed to establish the prevalence of low-grade inflammation in depression, using different C-reactive protein (CRP) levels, through a systematic literature review and meta-analysis.

Methods: We searched the PubMed database from its inception to July 2018, and selected studies that assessed depression using a validated tool/scale, and allowed the calculation of the proportion of patients with low-grade inflammation (CRP >3 mg/L) or elevated CRP (>1 mg/L).

Results: After quality assessment, 37 studies comprising 13 541 depressed patients and 155 728 controls were included. Based on the meta-analysis of 30 studies, the prevalence of low-grade inflammation (CRP >3 mg/L) in depression was 27% (95% CI 21-34%); this prevalence was not associated with sample source (inpatient, outpatient or population-based), antidepressant treatment, participant age, BMI or ethnicity. Based on the meta-analysis of 17 studies of depression and matched healthy controls, the odds ratio for low-grade inflammation in depression was 1.46 (95% CI 1.22-1.75). The prevalence of elevated CRP (>1 mg/L) in depression was 58% (95% CI 47-69%), and the meta-analytic odds ratio for elevated CRP in depression compared with controls was 1.47 (95% CI 1.18-1.82).

Conclusions: About a quarter of patients with depression show evidence of low-grade inflammation, and over half of patients show mildly elevated CRP levels. There are significant differences in the prevalence of low-grade inflammation between patients and matched healthy controls. These findings suggest that inflammation could be relevant to a large number of patients with depression.

Keywords: C-reactive protein; CRP; depression; immunopsychiatry; inflammation; low-grade inflammation; meta-analysis; mood; prevalence; review.

Publication types

  • Meta-Analysis
  • Research Support, Non-U.S. Gov't
  • Systematic Review

MeSH terms

  • Antidepressive Agents / therapeutic use
  • C-Reactive Protein / analysis*
  • Depressive Disorder / complications*
  • Depressive Disorder / drug therapy
  • Humans
  • Inflammation / blood
  • Inflammation / epidemiology*
  • Odds Ratio
  • Prevalence


  • Antidepressive Agents
  • C-Reactive Protein