## 4 Discussion  
In the analysis, a total of 13 studies were included. The studies were published within the timeframe of 2013-2023, encompassing locations such as the USA [18, 29, 30, 34, 36, 37], Qatar [26], Northern Portugal [16], Korea [9, 17], China [35], and Canada [27], and involving participants of both genders. The age of participants in the studies ranged from 1 to 80 years, and the sample size varied from 335 to 8896 individuals across all age groups. Out of the total studies reviewed, four were classified as having high quality [17, 29, 30, 34], six were categorized as having medium quality [9, 18, 26, 27, 36, 37], while only two exhibited low quality based on the Newcastle-Ottawa Scale [16, 35]. The present study examines the relationship between vitamin D levels and dental caries through a comprehensive systematic review and meta-analysis. For this association, no dose-response research has ever conducted done before. The findings of this systematic review and dose-response meta-analysis show a statistically significant relationship between the lowest 25[OH]D level and a higher risk of dental caries when compared to the highest level. However, it is crucial to note that the evidence's degree of certainty was rated as low. In addition, a linear dose-response study revealed that for every 10 nmol/L rise in 25[OH] D levels, there was an apparent 3% decrease in the risk of dental caries. Nonlinear dose-response analysis revealed a linear dose-dependent association as well. The relationship between serum vitamin D levels and the risk of dental caries has been evaluated in a number of prior systematic studies and meta-analyses. Although subgroup analysis according to the type of study revealed that cross-sectional and cohort studies found no significant difference in the relationship between the suboptimal vitamin D levels and dental caries risk, a recent meta-analysis found that suboptimal vitamin D concentration significantly increased caries risk in children (11%), which is similar to our finding [33]. In another meta-analysis which included 24 controlled clinical trials of children participants, where 22 of them were conducted before the modern design of trials, \begin{table}
\begin{tabular}{c c c c c c} \hline
**Variables** & **No. of Effect Sizes** & **OR (95\% CD)** & **P within a ** & **F2** & **P between b ** \\ \hline Overall & 16 & 1.41 (1.18, 1.68) & 0.001 & 61.9\% & - \\ Age group & & & & & \textless{}0.001 \\ Children & 10 & 1.15 (1.08, 1.23) & 0.557 & 0.0\% & \\ Adolescents & 3 & 1.56 (1.02, 2.39) & 0.653 & 0.0\% & \\ Children and youth & 2 & 1.29 (0.98, 1.71) & 0.721 & 0.0\% & \\ Adults & 1 & 2.83 (2.05, 3.90) & - & - & 0.132 \\ Adjustment for race/ethnicity & & & & & \\ Yes & 10 & 1.45 (1.08, 1.95) & 0.004 & 62.5 & \\ No & 6 & 1.15 (1.08, 1.23) & 0.458 & 0.0\% & \\ Adjustment for sugar consumption & & & & & 0.116 \\ Yes & 6 & 1.20 (0.95, 1.51) & 0.763 & 0.0\% & \\ No & 10 & 1.58 (1.22, 2.03) & \textless{}0.001 & 75.5\% & \\ Adjustment for gender & & & & & 0.067 \\ Yes & 12 & 1.48 (1.14, 1.91) & 0.001 & 57.1\% & \\ No & 4 & 1.15 (1.07, 1.23) & 0.414 & 0.0\% & \\ Adjustment for family income & & & & & 0.041 \\ Yes & 12 & 1.41 (1.06, 1.22) & 0.628 & 0.0\% & \\ No & 4 & 1.47 (1.16, 1.86) & 0.006 & 58.4\% & \\ Quality score c  & & & & & 0.345 \\ High & 6 & 1.20 (0.94, 1.53) & 0.614 & 0.0\% & \\ Medium & 8 & 1.55 (1.18, 2.03) & \textless{}0.001 & 79.8\% & \\ Low & 2 & 1.54 (0.93, 2.53) & 0.733 & 0.0\% & \\ Vitamin D categories & & & & & 0.108 \\ Q\({}_{\mathrm{N}}\) vs. Q\({}_{\mathrm{I}}\) & 7 & 1.15 (1.08, 1.23) & 0.837 & 0.0\% & \\ T\({}_{3}\) vs. T\({}_{1}\) & 4 & 1.31 (0.8, 2.13) & 0.191 & 36.9\% & \\ Q\({}_{\mathrm{I}}\) vs. Q\({}_{\mathrm{I}}\) & 5 & 1.89 (1.18, 3.01) & 0.001 & 69.9\% & \\
25 (OH)D assessment & & & & & 0.411 \\ Radioimmunoassay technique & 8 & 1.56 (1.11, 2.19) & \textless{}0.001 & 81.3\% & \\ Chromatography & 6 & 1.25 (1.03, 1.50) & 0.999 & 0.0\% & \\ Chemiluminescenceence & 2 & 1.54 (1.03, 2.30) & 0.793 & 0.0\% & \\ \hline \end{tabular}
\end{table}