Doctors, government agencies, and medical and dental societies have been arguing for decades whether or not vitamin D helps prevent tooth decay. In an effort to resolve the issue, researchers reviewed 24 clinical trials that took place from the 1920s through the 1980s, covering 2,827 children. Most of the studies preceded modern-day placebo-controlled design. 

These shortcomings aside, combining all results, doctors found that vitamin D supplements appeared to reduce the chances of tooth decay by 47 percent. Discussing their findings, researchers said the results suggest, with a low degree of certainty, that vitamin D reduces the chances of tooth decay. Because of the lack of studies more recent than the 1980s, doctors suggest new trials to bolster these preliminary findings and build confidence that vitamin D does indeed prevent tooth decay.

Reference: Nutrition Reviews Volume 71, Issue 2, pages 88–97, February 2013.