Change in neutrophil-to-lymphocyte ratio after acute and chronic exercise: a systematic review and meta-analysis

Chronic inflammation contributes to many common diseases, and exercise is a widely accessible tool to modulate it. This meta-analysis evaluates the neutrophil-to-lymphocyte ratio (NLR), a simple inflammatory marker, to better understand and optimize the anti-inflammatory effects of exercise. The present meta-analysis aims to systematically evaluate existing evidence on NLR changes induced by acute and chronic exercise. This study was registered in PROSPERO (CRD420251042422). Studies were selected based on PICO criteria: Population (P)-human participants regardless of age or health; Intervention (I)-acute or chronic exercise; Comparison (C)-NLR levels before exercise; Outcome (O)-within-subject change in NLR measured before and after exercise. We searched PubMed, EMBASE, Scopus, Web of Science, and the Cochrane Library extensively. Pooled results were expressed as mean difference (MD) with 95% confidence intervals (CIs) using STATA version 19.0. Twenty-six studies with a total of 1,203 participants were included. NLR levels showed no significant change immediately after acute exercise (MD = 0.03; 95% CI: -0.24 to 0.30; P = 0.82; k = 12, I² = 93.6%) but increased significantly 1-3 h postexercise (MD = 1.23; 95% CI: 0.46-1.99; P = 0.002; k = 5, I² = 93.3%). Chronic exercise was associated with a significant overall decrease in NLR (MD = -0.30; 95% CI: -0.56 to -0.04; P = 0.02; k = 15, I² = 98.4%). Studies with older participants reported greater reductions in NLR following chronic exercise. Sensitivity analysis confirmed that no single study had a disproportionate influence on the pooled estimates, and publication bias tests did not suggest bias. Acute exercise induces a transient increase in NLR between 1 and 3 h postexercise, whereas chronic exercise leads to sustained reductions, reinforcing the value of exercise as a nonpharmacologic strategy to reduce systemic inflammation, as reflected by this inflammatory marker.NEW & NOTEWORTHY Neutrophil-to-lymphocyte ratio (NLR) was unchanged immediately after acute exercise but increased significantly by 1-3 h later, reflecting a transient inflammatory response. Chronic exercise leads to a significant reduction in NLR, indicating long-term anti-inflammatory benefits. Studies with older participants reported greater reductions in NLR following chronic exercise.