Nutrition researchers based in Spain recently published a patient-centered review on vitamin D, where vitamin D is sourced (through either foods or sun exposure), and its relationship to skin cancer risk, citing epidemiological and human clinical studies published over the past decade. The aim of the review was to provide practical applications for maintaining an adequate vitamin D status, especially for people who are at heightened risk or have a personal history with melanoma or cutaneous cancer.
 
UV-related cancers, namely basal cell carcinoma, squamous cell carcinoma, and cutaneous malignant carcinoma, affect some 1,042,056 people worldwide, the authors noted, with a total mortality rate of 6%.
 
“Misnamed vitamin D is a true hormone that humans can synthesize upon sun exposure or through a balanced and healthy diet including vitamin D-rich foods or supplements,” the authors of the review wrote. “However, our current predominantly indoor lifestyle with unhealthy, intense, and sporadic sun exposure, along with other factors have contributed to the vitamin D deficiency epidemic. Paradoxically, this epidemic is accompanied by an increase in endemic skin cancer.”
 
The authors of the review included 62 references, which investigated vitamin D sourced from either and/or both UV exposure and foods, in an effort to provide context for the risk that UV exposure (which both provides the body with vitamin D and may increase skin cancer risk depending upon its extent) in order to look at the problematic effects of both UV exposure and sun avoidance in the context of cancer risk.
 
UV’s Dual Effect
 
“There seems to be little to no consensus among different specialists regarding the amount of sun exposure time they recommend their patients to synthesize enough vitamin D,” the authors noted. “In any case, advice on sun exposure should be adjusted to each patient’s characteristics, along with the specific geographic and climatic conditions. Understanding the UV index and the importance of sun exposure duration should be incorporated into our advice. Computerized decision aids and algorithms that take into account these complexities may be useful. There are also some promising experiences using wearable devices to promote UV exposure awareness. Finally, it is necessary that political institutions and health societies […] find common ground and common language to inform the general public without confusing them.”
 
Based on reviews of research spanning the past decade, the authors of the study found that there was conflicting evidence for each type of skin cancer, based on the dual effects that UV exposure has subsequently damaging DNA in skin cells while providing a key anti-carcinogenic vitamin.
 
In basal-cell carcinoma, for example, studies have shown that 100 daily units of either dietary or supplemental vitamin D or higher resulted in a linear increase in cancer risk, while a secondary analysis found that supplementation with vitamin D and/or calcium showed no benefit in basal-cell carcinoma risk. However, another study observed that serum vitamin D3 levels above 25 ng/mL may significantly reduce recurrence rates of BCC.
 
While there is an increase in squamous-cell carcinoma incidence in those with higher vitamin D serum levels in contemporary studies, this is probably confounded by excessive photodamage. “There is starting to be some epidemiological evidence that vitamin d and/or calcium supplementation may be useful to prevent SCC,” the authors said.
 
Adequate vitamin D levels are associated with a diminished risk of melanoma occurrence, although the various reviews on the matter tend to have different risk measures, the authors said.
 
While manuscripts don’t provide widely applicable strategies, the authors of the review proposed that public health authorities maintain recommendations for sun protection measures for people at heightened risk or with a personal history of skin cancer. They also recommend treating supplemental vitamin D as a functionally-identical means to that of sun exposure, and for this reason, it should be preferred. Lastly, “in patients with melanoma, or at risk of cutaneous cancer, serum vitamin D checks are warranted in order to detect and avoid this insufficiency,” they said.