Rates of melanoma, the deadliest form of skin cancer, have been rising for at least the last three decades, and this increase has been largely blamed on exposure to ultraviolet (UV) light from the sun. However, research published in the British Journal of Dermatology shows that the sun is likely nothing more than a scapegoat in the development of melanoma, and the sharp increase may actually be “an artifact caused by diagnostic drift.”
Diagnostic drift, according to the study, refers to a hefty increase in disease that is being fueled by non-cancerous lesions.
In fact, during the study period from 1991 to 2004, there were nearly 4,000 cases of melanoma included in the report, with an annual increase of 9.39 to 13.91 cases per 100,000 per year.
The researchers revealed that, rather than being fueled by increasing exposure to sunlight as is commonly suggested, the increased incidence was almost entirely due to minimal, stage 1 disease.
They noted: “There was no change in the combined incidence of the other stages of the disease, and the overall mortality only increased from 2.16 to 2.54 cases per 100,000 per year … We therefore conclude that the large increase in reported incidence is likely to be due to diagnostic drift, which classifies benign lesions as stage 1 melanoma.”
In other words, people are being diagnosed with melanoma skin cancer even when they have only a minimal, non-cancerous lesion, and these diagnoses appear to be skewing disease rates significantly. Further, adding even more credence to the growing body of evidence showing sun exposure is not the primary cause of melanoma, the researchers noted that the distribution of the lesions reported did not correspond to the sites of lesions caused by sun exposure.
They concluded: “These findings should lead to a reconsideration of the treatment of ‘early’ lesions, a search for better diagnostic methods to distinguish them from truly malignant melanomas, re-evaluation of the role of ultraviolet radiation and recommendations for protection from it, as well as the need for a new direction in the search for the cause of melanoma.”
Despite all the bad press linking sun exposure to skin cancer, there’s almost no evidence at all to support it. There is, however, plenty of evidence to the contrary. Over the years, several studies have confirmed that appropriate sun exposure actually helps prevent skin cancer. In fact, melanoma occurrence has been found to decrease with greater sun exposure, and can be increased by sunscreens.
One of the most important facts you should know is that an epidemic of the disease has in fact broken out among indoor workers. These workers get three to nine times LESS solar UV exposure than outdoor workers get, yet only indoor workers have increasing rates of melanoma — and the rates have been increasing since before 1940.
There are two major factors that help explain this, and the first has to do with the type of UV exposure.
There are two primary types of UV rays from sunlight, the vitamin-D-producing UVB rays and the skin-damaging UVA light. Both UVA and UVB can cause tanning and burning, although UVB does so far more rapidly. UVA, however, penetrates your skin more deeply than UVB, and may be a much more important factor in photoaging, wrinkles and skin cancers.
A study in Medical Hypotheses suggested that indoor workers may have increased rates of melanoma because they’re exposed to sunlight through windows, and only UVA light, unlike UVB, can pass through window glass. At the same time, these indoor workers are missing out on exposure to the beneficial UVB rays, and have lower levels of vitamin D.
Researchers wrote: “We hypothesize that one factor involves indoor exposures to UVA (321–400nm) passing through windows, which can cause mutations and can break down vitamin D3 formed after outdoor UVB (290–320nm) exposure, and the other factor involves low levels of cutaneous vitamin D3.
After vitamin D3 forms, melanoma cells can convert it to the hormone, 1,25-dihydroxyvitamin D3, or calcitriol, which causes growth inhibition and apoptotic cell death in vitro and in vivo.
… We agree that intense, intermittent outdoor UV overexposures and sunburns initiate CMM [cutaneous malignant melanoma]; we now propose that increased UVA exposures and inadequately maintained cutaneous levels of vitamin D3 promotes CMM.”
To put it simply, UVB appears to be protective against melanoma — or rather, the vitamin D your body produces in response to UVB radiation is protective.
As written in The Lancet: “Paradoxically, outdoor workers have a decreased risk of melanoma compared with indoor workers, suggesting that chronic sunlight exposure can have a protective effect.”
