BACKGROUND: There are differences in vitamin D levels between periodontitis and healthy individuals, but the effect of vitamin D on periodontitis is controversial. The purpose of this Meta-analysis is twofold: (1) compare vitamin D levels in individuals with or without periodontitis; (2) assess the effects of vitamin D supplementation during scaling and root planing (SRP) on periodontal clinical parameters in individuals with periodontitis. METHODS: A systematic search was conducted in five databases (PubMed, Web of Science, MEDLINE, EMBASE, and Cochrane library), published from the database inception to 12 September 2022. The Cochrane Collaboration Risk of bias (ROB) assessment tool, the risk of bias in non-randomized studies of intervention (ROBINS-I) tool, the Newcastle-Ottawa Quality Assessment Scale (NOS), and Agency for Healthcare Quality and Research (AHRQ) were used to evaluate randomized controlled trial (RCT), non-RCT, case-control study, and cross-sectional study, respectively. Statistical analysis was performed using RevMan 5.3 and Stata 14.0 software, with weighted mean difference (WMD), standardized mean difference (SMD) and 95% confidence intervals (CI) as the effect measures, and heterogeneity was tested by subgroup analysis, sensitivity analysis, Meta-regression. RESULTS: A total of 16 articles were included. The results of Meta-analysis showed that periodontitis was associated with lower serum vitamin D levels compared to normal population (SMD = -0.88, 95%CI -1.75 ~ -0.01, P = 0.048), while there was no significant difference in serum or saliva 25(OH)D levels between periodontitis and normal population. Additionally, the Meta-analysis showed that SRP + vitamin D and SRP alone had a statistically significant effect on serum vitamin D levels in individuals with periodontitis (SMD = 23.67, 95%CI 8.05 ~ 32.29, P = 0.003; SMD = 1.57, 95%CI 1.08 ~ 2.06, P < 0.01). And SRP + vitamin D could significantly reduce clinical attachment level compared to SRP alone (WMD = -0.13, 95%CI -0.19 ~ -0.06, P < 0.01), but had no meaningful effect on probing depth, gingival index, bleeding index, respectively. CONCLUSION: The evidence from this Meta-analysis suggests that the serum vitamin D concentration of individuals with periodontitis is lower than that of normal people, and SRP along with vitamin D supplementation has been shown to play a significant role in improving periodontal clinical parameters. Therefore, vitamin D supplementation as an adjuvant to nonsurgical periodontal therapy has a positive impact on the prevention and treatment of periodontal disease in clinical practice.