Background: In general, ovarian cancer incidence and mortality is higher in northern than southern latitudes. This ecologic study tests the hypothesis that vitamin D produced in the skin from sunlight exposure may be associated with a protective action in ovarian cancer mortality.
Methods: The association between average annual sunlight energy and age-specific ovarian cancer mortality rates in counties containing the 100 largest US cities was evaluated for 1979-1988. Simple linear regression was performed by decade using sunlight and ozone as independent variables and ovarian cancer rates as the dependent variable. Multiple regression was used to adjust for ozone and sulphur dioxide, since these atmospheric components may absorb ultraviolet light.
Results: Fatal ovarian cancer in these areas was inversely proportional to mean annual intensity of local sunlight in a univariate analysis (P = 0.0001), and in a regression adjusted for air pollution (P = 0.04). The association was also seen when restricted to 27 major urban areas of the US; however, probably due to a small sample size, this statistic did not reach significance.
Conclusions: This ecologic study supports the hypothesis that sunlight may be a protective factor for ovarian cancer mortality.