Discussion
periodontitis, PD
PERIODONTITIS, INFLAMMATORY DISEASE, TRANSFORMING
The Meta-analysis included both intervention and observational studies of varying quality, which will influence the interpretation of results. And high quality scores for both cross-sectional studies [The results of this meta-analysis showed that SRP + vitamin D could significantly reduce CAL compared to SRP alone. And similar to Machado V, et al. [At the same time, considering the large heterogeneity among the results of the Meta-analysis, stata14.0 software was used for sensitivity analysis through one-by-one elimination, which found that none of the results changed the direction, indicating that the included studies were stable. And subgroup analysis of study types, publication year, samples source (serum or saliva), measurement method of vitamin D (Elisa, HPLC–MS, CLIA), country, and gender showed that none of the above factors were sources of heterogeneity for the included studies. Given the lack of evidence of clinical heterogeneity, this Meta-analysis was performed using random-effects models.This Meta-analysis found there were statistically significant differences in serum vitamin D levels between individuals with periodontitis and healthy population, that is to say, periodontitis was associated with lower serum vitamin D levels compared with normal population. 25(OH)D is regarded as the best indicator of vitamin D status [The results of this Meta-analysis showed that either SRP alone or SRP combined vitamin D could increase the serum vitamin D concentrations in individuals with periodontitis. In addition, SRP + vitamin D was helpful to improve periodontal clinical indicators. And the Meta-analysis demonstrated that SRP + vitamin D reduced CAL compared to SRP, although there was no significant difference in the improvement of PD, GI, and BI between SRP + vitamin D and SRP. Studies have shown that periodontitis is an inflammatory disease closely related to autoimmune regulation, and early recognition of early biomarkers of periodontitis, such as Transforming Growth Factor-β1 (TGF-β1) and Vascular endothelial growth factor (VEGF), is crucial for the treatment and prognosis of periodontitis [In a preliminary cohort study, similar to this systematical review, periodontal individuals with higher plasma vitamin D levels had lower PD and CAL [This study has the following shortcomings. Firstly, although a comprehensive search of five major English databases was conducted, all the included studies were in English, and there was a lack of published studies in other languages, as well as a lack of grey literature database search, which may cause publication bias to some extent. Secondly, there was a great deal of heterogeneity among studies, and the sources of clinical heterogeneity of some outcome indicators were still not fully explained by subgroup analysis and sensitivity analysis. Thirdly, due to the limited number of high-quality studies (RCTs) evaluating the relationship between vitamin D and periodontitis, observational studies and intervention studies meeting the inclusion and exclusion criteria were included in this meta-analysis in order to more comprehensively analyze the relationship between vitamin D and periodontitis. Although confounding factors were strictly controlled for observational studies and subgroup analysis was performed based on study type. However, the heterogeneity results could not be changed, and these bias factors would inevitably affect the results of the meta-analysis. Therefore, the interpretation of the results of this study should be cautious.