In 2010, the Institute of Medicine (IOM) released a report that called for an increase in the recommended daily intake of vitamin D, but also said that the current body of research did not offer the evidence needed to confirm that vitamin D has the larger positive health effects its proponents claim it does.
Research has shown a positive link between vitamin D and oral and systemic health, the IOM noted; however, these studies have yielded "conflicting and mixed results and do not offer the evidence needed to confirm that vitamin D has these effects."
Now a new systematic review, conducted by Philippe Hujoel, PhD, DDS, MSD, MS, of the University of Washington School of Dentistry and School of Public Health, points to a positive association between vitamin D and lower rates of dental caries (Nutrition Reviews, November 9, 2012).
Vitamin D was first discovered in the early 1920s, and at least 20 prospective clinical studies evaluating its impact on dental caries were initiated in Europe, North America, and Asia over the next two decades, according to Dr. Hujoel. However, professional and governmental groups varied widely in their interpretation of the scientific evidence.
For example, the American Medical Association and the U.S. National Research Council concluded around 1950 that vitamin D was beneficial in managing dental caries, but the ADA said otherwise -- based on the same evidence. In 1989, the National Research Council, despite new evidence supporting vitamin D's caries-fighting benefits, called the issue "unresolved."
More recent reviews by the Institute of Medicine, the U.S. Department of Human Health and Services, and the ADA draw no conclusions on the vitamin D evidence as it relates to dental caries, Dr. Hujoel noted in a press release.
"Such inconsistent conclusions by different organizations do not make much sense from an evidence-based perspective," he said.
24 studies, 6 decades
For the Nutrition Reviews study, Dr. Hujoel analyzed 24 controlled clinical trials (CCTs) that met the inclusion criteria. The CCT quality was quantified using a 21-item questionnaire and content-specific measures such as method of treatment assignment, setting, clinician blinding, use of placebo, commercial funding source, and study duration.
The 24 CCTs included in the study spanned the 1920s to the 1980s and were conducted in the U.S., U.K., Canada, Austria, New Zealand, and Sweden in institutional settings, schools, medical and dental practices, or hospitals. All told, the CCTs encompassed nearly 3,000 participants between the ages of 2 and 16 years.
The trials increased vitamin D levels in these children through the use of supplemental ultraviolet (UV) radiation or by supplementing the children's diet with cod liver oil or other products containing the vitamin.
"My main goal was to summarize the clinical trial database so that we could take a fresh look at this vitamin D question," Dr. Hujoel said.
These trials showed that vitamin D was associated with a 47% reduction in the incidence of tooth decay, he noted. No robust differences could be identified between the caries-preventive effects of UV therapy and nutritional supplementation with either vitamin D2 or vitamin D3.
"The analysis of CCT data identified vitamin D as a promising caries-preventive agent, leading to a low-certainty conclusion that vitamin D in childhood may reduce the incidence of caries," Dr. Hujoel concluded.
The vitamin D question takes on greater importance in the light of current public health trends, he noted. Vitamin D levels in many populations are decreasing while dental caries levels in young children are increasing.
"Whether this is more than just a coincidence is open to debate," Dr. Hujoel said. "In the meantime, pregnant women or young mothers can do little harm by realizing that vitamin D is essential to their offspring's health. Vitamin D does lead to teeth and bones that are better mineralized."
Dr. Hujoel added a note of caution: "One has to be careful with the interpretation of this systematic review," he stated. "The trials had weaknesses which could have biased the result, and most of the trial participants lived in an era that differs profoundly from today's environment."
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