High vitamin D levels increase skin cancer risk in women
MedWire News: High levels of plasma vitamin D are associated with an increased risk for squamous cell carcinoma (SCC) and basal cell carcinoma (BCC) in women, report researchers.
Jiali Han (Harvard Medical School, Boston, Massachusetts, USA) and colleagues say that this link is likely to reflect the positive association between sun exposure and skin cancer risk, as a large percentage of circulating vitamin D present in the body is acquired through sun exposure.
The team prospectively assessed levels of plasma vitamin D at baseline (1989-1990) and their association with risk for SCC and BCC over the follow-up period (until 2007-2008) in 4641 middle-aged women participating in the Nurses' Health Study (NHS) and NHS II.
In total, 510 incident cases of BCC and 75 incident SCC cases were recorded over the follow-up period.
Han et al found that women in the highest quartile of plasma vitamin D (>34.2 ng/mL for NHS; >31.4 ng/mL NHS II) had a significant 2.07-fold increased risk for BCC compared with women in the lowest quartile (≤20.4 ng/mL NHS; ≤19.6 ng/mL NHS II). This association remained valid after adjusting for baseline age and season, lab batch, burning tendency, hair color, number of sunburns, and ultraviolet (UV)B flux of residence at blood collection.
However, the association with vitamin D level was most apparent in women who had blood collected outside the summer season, in those from areas with less UVB flux, and in light-pigmented women.
There was also a significant positive association between plasma vitamin D level and SCC risk after adjustment for the same confounders, with women in the top quartile for vitamin D having a 3.77-fold increased risk for SCC compared with those in the bottom quartile.
"Considering that most circulating vitamin D is due to sun exposure, the positive association between plasma vitamin D and non-melanoma skin cancer is confounded by sun exposure," say Han and team.
This "suggests that UV exposure may have a predominant adverse influence that exceeds any putative benefit from the higher levels of vitamin D," they add.
Concluding in PLoS ONE, Han and co-authors say: "Our results suggest that one-time measurement of plasma vitamin D may reasonably reflect long-term sun exposure and predict the risk of non-melanoma skin cancer."
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By Helen Albert