Vitamin D supplementation does not alter inflammatory markers in overweight and obese individuals: A systematic review and meta-analysis of randomized controlled trials

Chronic low-grade inflammation is a common feature of obesity and plays a crucial role in the progression of its complications. Vitamin D (VitD) plays an important role in modulating the immune response and regulating inflammation. Thus, this systematic review and meta-analysis aimed to evaluate the effects of isolated VitD supplementation on main inflammatory markers in overweight and obese individuals with no comorbidities and with VitD deficiency. We hypothesized that the increase in serum VitD concentrations after supplementation would significantly reduce the concentrations of inflammatory markers. The search was conducted in Medline/PubMed, SCOPUS, EMBASE, and Web of Science. Eleven randomized placebo-controlled studies were included in the final analysis, with a total of 504 participants and daily (1,000 - 7,000 IU) or bolus (100,000 - 200,000 IU) doses of VitD lasting from 2 to 26 weeks. The VitD supplementation did not influence C-reactive protein (CRP) (MD: 0.01; 95% CI -0.37, 0.39; P = 0.97), interleukin-6 (IL-6) (MD: -0.34; 95% CI -1.09, 0.42; P = 0.38), and tumor necrosis factor (TNF) concentrations (MD: -0.02; 95% CI -0.23, 0.19; P = 0.85). In the analysis considering the studies with a significant increase in serum VitD concentrations, VitD supplementation also did not influence CRP (MD: -0.17; 95% CI -0.88, 0.54; P = 0.64), IL-6 (MD: -0.47; 95% CI -1.31, 0.37; P = 0.27), and TNF concentrations (MD: 0.01; 95% CI -1.34, 1.37; P = 0.98). This meta-analysis suggests that VitD supplementation does not significantly alter inflammatory markers in overweight and obese individuals.