To Örebro University

BACKGROUND: It has been suggested that sunlight through production of vitamin D might have a protective effect on a number of internal cancers. Consequently, in spite of the well known skin cancer risks, some researchers advocate more exposure to ultraviolet radiation, supported by the solarium industry. We estimated the risk of internal cancer before the patient contracted a basal cell carcinoma (BCC) of the skin, the most common cancer in white populations and strongly associated with extensive sun exposure.

METHODS: A nested case control study was undertaken in the whole Swedish population. 115,016 patients with BCC and 987,893 controls were linked to population based registers.

FINDINGS: The cases had an increased risk of getting another form of cancer before the BCC diagnosis: odds ratio (OR)=1.84; 95% confidence interval (CI) 1.81-1.86. This risk was mainly due to skin cancer: OR=4.95; 95% CI 4.81-5.09 but also non-skin cancer risk was elevated: OR=1.37; 95% CI 1.35-1.39. We adjusted the estimates for age, level of income, occupational status in national censuses, place of living and sex, where appropriate. Of the cancers specifically suggested to be related to vitamin D status: colon, prostate, breast, and ovary cancer, all had slightly increased ORs whilst for pancreatic and gastric cancer no increased OR was found.

INTERPRETATION: Patients with BCC, a proxy for extensive sun exposure, run an increased risk of other forms of cancer prior to the diagnosis of BCC. The findings in this study contradict that vitamin D production through extensive sun exposure has any protective effect on internal cancer but emphasise the increased risk for skin cancer.