THE INFLUENCE OF LATITUDE AND DISTANCE FROM SEACOAST ON DENTAL DISEASE

¹ Harvard University, Boston, Mass.

A number of large studies of dental disease in the United States, South Africa, Australia, and New Zealand are analyzed graphically and statistically. While none of these studies offer all one could wish in either quality or quantity, they merit our best efforts at interpretation, if only to stimulate more and better work in the future.

A suggestive pattern emerges for the United States showing dental disease (chiefly caries) to increase with latitude and with distance from seacoast. Both of these relationships are verified by calculations which show statistically significant correlation coefficients. In observations from the Southern Hemisphere a similar pattern, inverted, is found in South Africa. This, too, is statistically significant. Variation with latitude is apparent in Australia.

A group of climatological factors, together with the chemical composition of water supplies, probably account for most of the variations in dental disease. The climatological factors are sunshine, rainfall, temperature, and relative humidity-all more or less related to one another. The relation of sunshine to dental disease is confirmed in this study, that of relative humidity demonstrated.

The major factors involved in variation with latitude appear to be sunshine and temperature. Variation in mean annual hours of sunshine present a pattern much like that for dental disease in the United States, with considerable latitude changes. Statistical correlations are significant. Temperature varies almost entirely with latitude and may be linked to dental caries through its effect on the caloric requirements and water intake of humans. The consumption of carbohydrate food seems to be greater in northern latitudes.. Urbanization has been claimed as a reason for higher dental caries in the north. Data from forty-one cities in the United States show caries to be slightly, but not significantly, higher in these cities than in adjoining rural areas.

The major factors involved in variations with distance from seacoast appear to be fluorides, total water hardness, and relative humidity. Fluoride is most common in deep-well waters, and deep wells are most common in inshore areas. The persistence of caries variation in South Africa, even after the removal of high fluoride communities there, returns our attention to water hardness and to climatological factors. Relative humidity in the United States presents a pattern much like that for dental disease except that a "plateau" exists in the eastern states from just back of the immediate seacoast to the Mississippi Valley, with none of the variations seen for dental disease in this area. Sunshine varies somewhat with distance from seacoast, but decreases as one proceeds inshore from the Atlantic Coast. Rainfall decreases as one proceeds inshore from either ocean, but does not present a geographical pattern like that for dental disease.

It is hoped that identification of major geographic trends in the prevalence of dental disease will permit a more systematic approach to the epidemiology of dental caries. This may lead to productive new studies on specific etiological factors and may provide valuable clues to more basic research. At the very least, it can provide the basis for estimating treatment needs in different areas.