In all of these studies, significant inverse correlations between the vitamin D indices and endometrial cancer incidence and/or mortality rate were found.
The studies by Grant were based on the Atlas of Cancer Mortality Rates in the United States6. The geographical variation of endometrial 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. The geological variation of July solar UVB dose was used in the U.S. This index is highly asymmetrical7, being high in the southwest and low in the northeast due to variations in surface elevation and stratospheric ozone layer.
In Europe, latitude was used as the index of vitamin D8.There is also an ecological study using data from France that found significantly reduced risk of endometrial cancer with respect to increasing latitude9.
In a global multi-country study10, calculated solar UVB doses and cloud cover were used for the vitamin D index. Indices for other risk modifying factors, such as smoking, alcohol consumption were also used in the United States after the 2002 study 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.
A study in Sweden reported a beneficial effect of UV irradiance in reducing the risk of endometrial cancer:
Among the 17,822 postmenopausal women included, 166 cases of endometrial cancer were diagnosed. We used a multivariate Cox regression analysis adjusting for age and other selected demographic variables to determine the risk of endometrial cancer. Women using sun beds >3 times per year reduced their hazard risk (HR) by 40% (0.6, 95% confidence interval (CI) 0.4-0.9) or by 50% when adjusting for body mass index or physical activity (HR 0.5, 95% CI 0.3-0.9), and those women who were sunbathing during summer reduced their risk by 20% (HR 0.8 95% CI 0.5-1.5) compared with women who did not expose themselves to the sun or to artificial sun (i.e., sun beds)11.
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 where it is warm enough to expose sufficient skin area while in the sun to produce a reasonable amount of vitamin D.
A study in Australia, Singapore and Spain found reduced incidence of endometrial cancer after incidence of basal cell or squamous cell carcinoma, albeit statistically insignificant due to low numbers of cases12.
Page last edited: 22 August 2011
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