Most of the studies relating to sunlight exposure and risk of esophageal cancer are ecological studies conducted in the U.S.12345. However, there are also ecological studies finding reduced risk of esophageal cancer incidence and/or mortality rates in China6 [Grant, 2007], France7, and Japan8.
The two studies by Grant were based on the Atlas of Cancer Mortality Rates in the United States9. The geographical variation of esophageal cancer mortality rates in the U.S. is very similar to that for breast cancer, which has strong support as a vitamin D sensitive cancer. Rates were highest in the northeast and lowest in the south, with intermediate rates along the west coast, which has lower solar UVB doses in summer than inland due to the prevailing winds bringing in fog and clouds.
The geological variation of July solar UVB dose was used in the U.S. This index is highly asymmetrical10, being high in the Southwest and low in the Northeast due to variations in surface elevation (higher in west) and stratospheric ozone layer (thinner in west). The U.S. ecological study5 found somewhat lower inverse correlation with solar UVB doses for July than for breast, colon, and rectal cancer11. Alcohol and smoking are stronger risk factor for esophageal cancer12 than the other three types of cancer5, which may explain the different finding.
Indices for other risk modifying factors, such as smoking, alcohol consumption were also used in the United States after 2002 and dietary factors were added to the multi-country studies in order to rule out well-known cancer risk factors that might affect the geographical variation and interpretation of the results. In all of these studies, significant inverse correlations between the vitamin D indices and esophageal cancer incidence and/or mortality rate were found.
A comparison of esophageal cancer mortality rates as a function of altitude of United States counties for the period 1950-69 was reported by Amsel et al13. Counties were divided into those below 1000 feet and above 3000 feet, and counties with cities with populations greater than 100,000 inhabitants were omitted since there are few such cities at high altitudes. For males, standardized mortality rates (SMRs) varied from 0.40 (95% CI, 0.22-0.66) to 0.78 (0.70-0.87) depending on degree of industrialization, Hispanic heritage, or urban residence. For females, (SMRs) varied from 0.55 (0.22-1.13) to 0.74 (0.61-0.89). While no explanation for the finding was given, the results are consistent with higher solar UVB doses at higher altitudes. UVB doses increase by about 19% per 1000 m (3300 ft) on an annual basis in Austria14.
A significant inverse correlation of esophageal cancer mortality rates with respect to non-melanoma skin cancer (NMSC) mortality rates for males but not females was also found in an ecological study of cancer mortality rates in Spain15.
A study in Australia, Singapore and Spain found statistically insignificant reduced incidence of esophageal cancer after incidence of basal cell or squamous cell carcinoma16.
Page last edited: 22 August 2011
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