Large geographical variations in dental health and tooth loss among U.S. adolescents and young adults have been reported since the mid-1800s. The first study finding a north-south gradient in dental caries was a report of men rejected from the draft for the Civil War for lost teeth, from 8 per 1000 men in Kentucky to 25 in New England.
Studies by Clarence Mills and Bion East in the 1930s first linked the geographical variation in prevalence to sunlight exposure. They used data for adolescent males aged between 12 and 14 years from a cross-sectional survey in 1933–1934. East later found that dental caries were inversely related to mean hours of sunlight/year, with those living in the sunny west (3000 hours of sunlight/year) having half as many carious lesions as those in the much less sunny northeast (<2200 hours of sunlight/year).
Several studies conducted in Oregon in the 1950s noted that dental caries prevalence was lower in the sunnier regions of the state than in the cloudy regions, a finding that persisted after considering other factors that affect dental caries rates. The mechanism was attributed to vitamin D through its effects on calcium metabolism.
There were also several studies reported on vitamin D and dental caries in the 1920s and 1930s. May Mellanby and coworkers in Sheffield, England, did studies on the role of vitamin D on teeth in the 1920s. 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. 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/d to prevent caries effectively.
The mechanism whereby UVB reduces risk of dental caries is through production of vitamin D, followed by induction of cathelicidin, which attacks oral bacteria linked to dental caries. Cathelicidin is well known to fight bacterial infections, with findings reported for several bacterial infections including pneumonia, sepsis, and tuberculosis. Several recent papers reported that cathelicidin reduces the risk of caries, but did not link cathelicidin to vitamin D.
Serum 25-hydroxyvitamin D concentrations around 30-40 ng/ml (75-100 nmol/L) should significantly reduce the formation of dental caries. (The average white American has a level near 25 ng/ml, while the average black American has a level near 16 ng/ml.) To obtain these levels, oral intake of 1000-4000 IU/d of vitamin D3 or 15-20 minutes in the sun near solar noon in summer with 20-30% body surface area exposed is suggested.
Good dental health also involves a healthy diet low in sugar, regular tooth brushing, and regular dental checkups.
Use of vitamin D appears to be a better option for reducing dental caries than fluoridation of community water supplies, as there are many additional health benefits of vitamin D and a number of adverse effects of water fluoridation such as fluorosis (mottling) of teeth and bones.