Good evidence exists that solar ultraviolet-B and vitamin D reduce the risk of ovarian cancer




A recent paper concluded that there was no consistent or strong evidence that vitamin D reduces the risk of ovarian cancer. However, a more careful review finds the evidence to be strong and consistent.


Ecological studies provide the strongest support. Reference 21 in a published report was not published in a peer-reviewed journal, and it is not readily available. Reference 26 in that report found that nonmelanoma skin cancer mortality rate in 48 continental provinces was significantly inversely correlated with ovarian cancer mortality rate (normalized correlation coefficient –0.51). That index was a better index of solar ultraviolet B (UVB) irradiance than latitude in Spain. In reference 27, the authors reported relative risk for ovarian cancer mortality rate was 1.09 (95% confidence interval, 1.06–1.11) for low vs high UVB. Thus, 7 of the 10 ecological studies found significant inverse relations between indices for solar UVB and ovarian cancer.


Case-control studies were either supportive or inconclusive.


Three cohort studies investigated oral intake of vitamin D to values below about 900 IU/day with cohort mean values ranging from 325 to 350 IU/day. These studies did not find significant correlations, although the risk ratios were often greater than 1 for the highest oral intakes. Oral intake is not the only source of vitamin D, and those in low UVB-dose regions might take more oral vitamin D to compensate, possibly explaining the direct correlations.


It was pointed out earlier that oral intakes of 400 IU/day had no benefit for colorectal cancer, the cancer with the strongest evidence for a protective role of vitamin D. Each 1000 IU/day increases serum 25-hydroxyvitamin D [25(OH)D] levels by about 10 ng/mL. On the other hand, casual UVB irradiance in summer in the United Kingdom for those aged 45 years increases serum 25(OH)D by 15 ng/mL.


Summertime solar UVB dose has a significant inverse correlation with ovarian cancer in the United States (reference 19 1 ). Based on published metaanalyses for breast and colorectal cancer incidence vs serum 25(OH)D levels, an increase of 15 ng/mL reduces incidence by about 25%. Thus, ecological studies should easily find inverse correlations with respect to solar UVB in the United States. However, expected risk reductions in oral intake studies would be less than 8%, which is lower than typical 95% confidence intervals.


Disclosure


I receive funding from the UV Foundation (McLean, VA), the Sunlight Research Forum (Veldhoven), Bio-Tech-Pharmacal (Fayetteville, AR), and the Vitamin D Council (San Luis Obispo, CA).

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Jun 21, 2017 | Posted by in GYNECOLOGY | Comments Off on Good evidence exists that solar ultraviolet-B and vitamin D reduce the risk of ovarian cancer

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