Indoor Tanning a Gianus Bifrons: Vitamin D and Human Cancer

Despite it is now undeniable that indoor tanning exposure is associated with a number of skin cancers, its favorable effects on vitamin D status may bear some underestimated and currently unexplored health benefits. Vitamin D is a fat-soluble vitamin naturally present in a limited number of foods, the concentration of which largely depends on ultraviolet (UV) B sources exposure in humans. A strong, graded, and inverse association has been documented between serum vitamin D and the risk of developing certain types of malignancy, especially colorectal, breast, lung, bladder, and kidney cancers. The overall mortality from any type of cancer is also apparently lower in subjects with increased values of serum vitamin D. Both genomic and nongenomic mechanisms have been identified to support the anticancer effects of vitamin D. Notably, UVB radiation emitted from indoor tanning devices is effective to linearly increase the serum vitamin D concentration, up to twofold. Therefore, some favorable effects against the risk of developing many human diseases, including nonskin cancers, cannot be excluded at first glance, although they may not be only linked to vitamin D status. Further large, prospective or randomized studies should be hence planned to definitely establish whether the unfavorable effects of indoor tanning exposure on skin cancers may be outweighed by the still unexplored benefits attributable to amelioration of vitamin D status.