Brief report
Role of Ultraviolet B Irradiance and Vitamin D in Prevention of Ovarian Cancer

https://doi.org/10.1016/j.amepre.2006.08.018Get rights and content

Background

There is a north–south gradient in age-adjusted mortality rates of ovarian cancer in the United States, with the highest rates in the Northeast and the lowest in the South through Southwest. This suggests that lower levels of solar irradiance might be associated with higher risk of ovarian cancer. Laboratory findings also suggest that low levels of vitamin D metabolites could play a role in the etiology of ovarian cancer.

Methods

The association of solar ultraviolet B (UVB) irradiance, stratospheric column ozone, and fertility rates at ages 15 to 19 years with incidence rates of ovarian cancer in 175 countries in 2002 were examined using multiple linear regression in 2006.

Results

Age-adjusted ovarian cancer incidence rates generally were highest in countries located at higher latitudes (R2=0.45, p≤0.01). According to multivariate analysis, UVB irradiance (p≤0.002) and fertility rates at ages 15 to 19 (p=0.01) were inversely associated with incidence rates, while stratospheric ozone (p≤0.0008), which reduces transmission of UVB, was positively associated with incidence (R2=0.49, p<0.0001).

Conclusions

Solar UVB irradiance was inversely associated with incidence rates of ovarian cancer in this study, adding new evidence to the theory that vitamin D might play a role in the prevention of ovarian cancer. Cohort studies are needed to confirm this possible association.

Introduction

There are approximately 20,200 new cases and 15,300 deaths from cancer of the ovary each year in the United States,1 but little is known about its etiology. Mortality rates from ovarian cancer are lowest in areas of the United States with high solar irradiance2, 3 and solar ultraviolet B (UVB),4 similar to the pattern of lower rates in these areas of colon5 and breast cancer in Canada,6 the United States,7 and the former Soviet Union.8

Greater exposure to solar UVB in areas with high solar irradiance results in greater cutaneous photosynthesis of vitamin D in populations in these areas, resulting in higher levels of anticarcinogenic vitamin D metabolites.5

Of six studies of sunlight or UVB and ovarian cancer,2, 3, 4, 9, 10, 11 four2, 3, 4, 9 reported higher mortality rates associated with lower regional sunlight, although two reported no association in Norway10 and Japan.11 A case–control study reported that low oral vitamin D intake was associated with twice the risk of ovarian cancer.12 The present study characterizes differences in ovarian cancer incidence rates in 175 countries according to latitude, solar UVB irradiance, stratospheric ozone, and fertility rates.

Section snippets

Data Sources

Age-adjusted incidence rates of ovarian cancer were obtained for 175 countries using the International Agency for Research on Cancer (IARC) GLOBOCAN database.13 GLOBOCAN uses national cancer registries and vital events registers to estimate annual age-adjusted incidence rates per 100,000 population in 175 countries. The latest year for which complete data were available was 2002.

A file was created that contained information for each country on solar UVB irradiance at the top of the atmosphere

Results

Ovarian cancer incidence was in general highest at the highest latitudes in both hemispheres (R2=0.45, p<0.01) (Figure 1). After including UVB irradiance, stratospheric ozone, and fertility rates at ages 15 to 19 in a regression model, UVB irradiance (p<0.01) and fertility rates at ages 15 to 19 (p=0.002) were inversely associated with incidence rates, while stratospheric ozone (p=0.0008) was positively associated with incidence rates (R2=0.49, p<0.0001) (Table 1).

Discussion and Conclusion

Only modest progress has been made to date in understanding the etiology of ovarian cancer. The main associations that have been reported are a positive association with nulliparity,17 and higher number of ovarian cycles,18 and a negative association with oral contraceptive use.19 One observational study of the effect of vitamin D on ovarian cancer risk was found in the literature search.12 It reported an odds ratio of 0.43 (p<0.01) in women who consumed more than 360 IU per day of vitamin D

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