Vitamin D levels show complex link with skin cancer
MedWire News: High levels of vitamin D in the body are positively associated with the development of non-melanoma skin cancer (NMSC), US experts believe.
They say that their findings add to the "limited and conflicting" scientific evidence and call for more work to better understand the "complex relationship" between vitamin D and skin cancer.
NMSC is the most common form of cancer in the USA and has become steadily more common over the past few decades. A main cause of NMSC is solar radiation, or sunlight, which is also known to stimulate the production of vitamin D within the skin.
Food is the other source of vitamin D; the vitamin is naturally present in fish, eggs, and liver, and in some countries it is artificially added to staple foods such as bread and milk.
There is much controversy over the association between vitamin D levels in the body and the risk for skin cancer. Some studies have found that vitamin D can prevent a form of NMSC called basal cell carcinoma (BCC), a possibility that was investigated by Melody Eide (Henry Ford Hospital, Detroit, Michigan) in the present study.
Eide's team used a health insurance database to identify 3223 patients with weak or fragile bones, a condition known as osteoporosis. They were chosen for the study because osteoporosis is frequently associated with low levels of vitamin D.
In all, 2257 patients were found to have insufficient levels of vitamin D in their blood (defined as levels below 30 ng/ml). In addition, 240 patients had been diagnosed with NMSC - either BCC or the alternate form, squamous cell carcinoma (SCC).
The analysis found that people with vitamin D levels above 15 ng/ml were markedly more likely to have NMSC than those considered to be vitamin D "deficient."
This association held true after accounting for known risk factors for NMSC. It also applied equally to cancers on parts of the skin that were and were not routinely exposed to sunlight.
Writing in the Archives of Dermatology, the researchers say that higher vitamin D levels in the blood are directly associated with a higher likelihood of developing skin cancer. However, they admit that the association is complex and the underlying pathways not well understood.
"The complex and confounded relationship of vitamin D, ultraviolet, and NMSC makes classic epidemiological investigation difficult in the absence of carefully measured history of cumulative ultraviolet exposure," they remark.
MedWire (www.medwire-news.md) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2011
By Joanna Lyford