Inverse correlations with UVB have been found after taking other risk factors into account, such as smoking and alcohol consumption.
Exposure to sunlight is a useful indicator of the level of vitamin D in a population.
The studies by Grant were based on the Atlas of Cancer Mortality Rates in the United States6. The geographical variation of gastric cancer mortality rates in the U.S. is very similar to that for breast and colon cancer, which also have strong support as vitamin D sensitive cancer5. 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.
Gastric cancer rates are elevated near the U.S.-Mexico border due to the high fraction of Hispanic residents; gastric cancer rates are high in those countries due to H. pylori infection from inadequate sanitation facilities and transmission in domestic water systems7. Due to treatment of H. pylori infection with antibiotics, gastric cancer rates have decreased dramatically in the U.S89.
The geographical variation of July solar UVB dose was used in the U.S. as the index of vitamin D production. This index is highly asymmetrical10, being high in the southwest and low in the northeast due to variations in surface elevation and stratospheric ozone layer. These correlations were found after adjustment for other risk factors. Indices for other risk factors, such as smoking, alcohol consumption were used in the United States5 in order to rule out well-known cancer risk factors that might affect the geographical variation and interpretation of the results.
Indices of solar radiation levels were inversely correlated with gastric cancer mortality rates in an ecological study in Japan11. Latitude was directly correlated with gastric cancer mortality rates in an ecological study for China12 as well as in Spain13.
Another ecological study in China using in 305-nm average daily ambient solar UVB radiation determined from a NASA satellite instrument, also found an inverse correlation for incidence and mortality rates of gastric cancer14.
Other vitamin D indices also show an association with lower rates of gastric cancer. Non-melanoma skin cancer (NMSC) is often an index of high personal solar UVB irradiance. Thus, it can be used as a long-term vitamin D index in sunnier countries. A study in Australia, Singapore and Spain found statistically insignificant reduced incidence of gastric cancer after incidence of basal cell or squamous cell carcinoma15.
Page last edited: 22 August 2011
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