In summary: There is not sufficient evidence to show that Vitamin D has a preventative effect on dental caries. It is plausible, and following the recommended intake of Vitamin D is important for a number of health reasons, but there is no solid evidence to show that it alone is adequate for the prevention of dental caries. Fluoride, on the other hand, has been shown to prevent dental caries.
Firstly, I would like to address the Dr. Mercola claim, as there's some fishy conflict of interest stuff going on here:
Most of the original Mercola article quotes an article from the "Vitamin D Council", which itself is a restated version of a paper from the Sunlight, Nutrition and Health Research Center (Sunarc) called A review of the role of solar ultraviolet-B irradiance and vitamin D in reducing risk of dental caries. Indeed, the "Vitamin D Council" article is written by the very same man that wrote this paper for Sunarc.
I have a number of issues with this paper:
- The obvious conflict of interest - this center promotes Vitamin D as a cure for nearly everything, appears to have just the one author, and its website spruiks books by the same author. I have no issue with this if it was stated anywhere as a conflict of interest, but it's not. He makes his living selling books that rely on the studies performed by his center and therefore probably wants them to fit his agenda.
- The study performs meta-analyses on these studies from the 1920s and 30s, but does not address any of the potential flaws in those studies
- The abstract concludes with "It is unfortunate that the UVB and vitamin D findings were not given more consideration in the 1950s as a way to reduce the risk of dental caries when water fluoridation was being proposed." This screams "agenda" to me, as the study should control for water fluoridation but not hold a position on the practice.
But, let's leave that aside and have a look at each of the studies cited by the Vitamin D council. (Why can't they link to the studies directly?) Firstly,
May Mellanby and coworkers in Sheffield, England, did studies on the role of vitamin D on teeth in the 1920s.
Probably refers to this paper (PDF warning) "The Action of Vitamin D in Preventing the Spread and Promoting the Arrest of Dental Caries in Children" (1928).
The first experiments were with dogs, where it was found that vitamin D stimulated the calcification of teeth. Subsequently, they studied the effect of vitamin D on dental caries in children, finding a beneficial effect.
I'm not going to comment on the dog study, but my 1928 citation above discusses a 1924 study by the same group and notes the very large flaw that the two diets compared had vast differences aside from vitamin D content. Most notably the vitamin A levels lower and processed grains were higher in the control group than the vitamin D group. I'll therefore just focus on this 1928 study.
A cursory glance shows:
- The study is not blinded or randomised
- The groups used in the study contained children of different ages and they therefore cannot be directly compared
- The groups were small (18-20 children per group)
- They did not control for dental hygeine, i.e. tooth brushing or flossing.
- They did not control for sun exposure (one of the major sources of vitamin D) or season
- They did not measure vitamin D levels in the participants.
I would have trouble saying anything about vitamin D based on this study.
The Vitamin D council quotation continues:
Additional studies were conducted on children in New York regarding dental caries with respect to season, artificial ultraviolet-B (UVB) irradiance, and oral intake of vitamin D with the finding that it took 800 IU/day to prevent caries effectively.
Again, I can only assume they mean the 1938 study by the same author (PDF) titled "The Role of Vitamin D in the Control of Dental Caries in Children".
This study tracks groups of children across the seasons in New York and has some groups exposed to UVB by a lamp, others take cod liver oil and others a vitamin D supplement of a specific dose.
There are several similar problems to the previous study:
- The trial is not blinded or randomised
- They did not control for dental hygeine, i.e. tooth brushing or flossing.
- They did not control for sun exposure (one of the major sources of vitamin D)
- They did not directly measure vitamin D levels in the participants.
Again, though I would be extremely hesitant to draw any conclusions, some of their results showed a decrease in the occurrence of dental caries with increasing doses of vitamin D when administered in the same fashion. At best, I would say "There may be a correlation" based on these studies.
The "Vitamin D Council" or "Sunlight, Nutrition and Health Research Center", however, find this evidence solid enough to include in their meta-analysis, which concludes that
Serum 25-hydroxyvitamin D concentrations around 30-40 ng/ml (75-100 nmol/L) should significantly reduce the formation of dental caries
I probably wouldn't draw the same conclusion based on that evidence, as I wouldn't have included these studies from the 1920s and '30s. But is there anything more recent and scientifically rigorous available?
(To be completed: a review of any recent studies including vitamin D serum levels and any correlation/causation with dental caries)
Estimation of optimal serum concentrations of 25-hydroxyvitamin D for multiple health outcomes(2006) says:
Thus, although data vitamin D and dental health outcomes are limited, available evidence suggests that serum 25(OH)D concentrations between 90 and 100 nmol/L are desirable.
(This study only found sufficient data relating to tooth loss in elderly patients)
At this stage, I am unable to find any recent studies showing that vitamin D serum levels have a preventative effect on dental caries. Vitamin D is important for a host of other reasons, but there is not sufficient evidence to recommend its use in place of Water Fluoridation, which has been proven effective (PDF) for over 50 years at decreasing the incidence of dental caries.
