Twenty-four controlled clinical trials were included in the review (2,827 participants). The quality score ranged from 6 to 21 (mean 14.8). Three trials used random assignment. Eleven trials were cluster-randomised. Non-comparability in baseline caries score between intervention and control groups was present in four trials. There was a lack of outcome assessor blinding in nineteen trials. Fourteen trials did not use placebo as control. The median drop-out rate was 47% (where reported).The median duration of follow-up was 12 months.
Supplemental vitamin D was associated with a significant reduction in the incidence of dental caries compared with no supplement (RR 0.53, 95% CI 0.43 to 0.65; 38 comparisons). Significant heterogeneity was observed for this outcome (p<0.0001).
Subgroup analyses showed that compared with no supplement, supplemental ultraviolet radiation (RR 0.36, 95% CI 0.17 to 0.78), vitamin D3 (RR 0.51, 95% CI 0.40 to 0.65) and vitamin D2 (RR 0.64, 95% CI 0.48 to 0.86) were associated with a significant reduction in dental caries.
Sensitivity analysis showed that no individual trial had a large impact on the summary estimate. Results of meta-regressions were also reported.
There was evidence of publication bias.