Ovarian cancerExposure to sunlight

Most of the studies relating to sunlight exposure and risk of ovarian cancer are ecological studies conducted in the U.S1 2 3 4.  The two studies by Grant were based on the Atlas of Cancer Mortality Rates in the United States5.  

The geographical variation of ovarian 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 geographical variation of July solar UVB dose was used in the U.S as an index of exposure to sunlight.  This index is highly asymmetrical6, being high in the southwest and low in the northeast due to variations in surface elevation and stratospheric ozone layer. 

There are also two multi-country ecological studies7 8.  In Europe, latitude was used as the index of vitamin D7.  In the global multi-country study, calculated solar UVB doses and cloud cover were used for the vitamin D index.

Lower rates of ovarian cancer are seen in areas that have more sunlight.

Indices for other risk modifying factors, such as smoking, alcohol consumption were also used in the United States in studies conducted 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 ovarian cancer incidence and/or mortality rate were found.  While a review regarding ovarian cancer concluded that the evidence for UVB and vitamin D was not strong9, it was pointed out in a letter to the editor that most of the observational studies did not consider high enough oral intake or serum 25(OH)D levels and that the ecological studies were in essential agreement about an inverse correlation between solar UVB and ovarian cancer incidence and/or mortality rate10.

A composite death certificate based case-control study found that living in a high UVB dose region of the U.S. was associated with statistically significant reduced risk of ovarian cancer mortality rate, but no statistically significant finding was made with respect to UV dose from occupation or other factor11.

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 highly significant inverse correlation of ovarian cancer mortality rates with respect to NMSC mortality rates was also found in an ecological study of cancer mortality rates in Spain12

A study in Australia, Singapore and Spain found statistically significant reduced incidence of ovarian cancer after incidence of basal cell or squamous cell carcinoma13

Page last edited: 18 July 2011


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