Increased UVA exposures and decreased cutaneous Vitamin D3 levels may be responsible for the increasing incidence of melanoma
This paper may enlighten, or upset, dermatologists mired in the "sunlight causes cancer" myth. It also has the potential to damage the sunscreen industry, also based on the myth that sun exposure causes skin cancer.
The authors, Dianne E. Godar, Robert J. Landry, and Anne D. Lucas propose that intermittent, intense exposure to UVB initiates cutaneous malignant melanoma (CMM), but that promotion of CMM requires increased UVA exposures and inadequately maintained cutaneous levels of vitamin D3.
Some interesting facts cited in support of their hypothesis:
- "Although outdoor workers get much higher outdoor solar UV doses than indoor workers get, only the indoor workers’ incidence of cutaneous malignant melanoma (CMM) has been increasing at a steady exponential rate since before 1940."
- "Outdoor workers have a lower incidence of CMM compared to indoor workers."
- People who use UVB-absorbing sunscreens have a significantly increased risk of melanoma and these sunscreens promote the growth of melanoma in mice.
- People who maintain an all-year-tan have a reduced risk of melanoma, and outdoor workers, who receive three to nine times the erythemally effective UV dose of indoor workers have a significantly lower incidence of melanoma.
- Excluding sunburns, outdoor activities in childhood decrease the incidence of melanoma and research has failed to find a ‘‘critical period,” such as childhood, where intense exposures contribute more towards the induction of melanoma.
- Sunburns throughout life increase the risk of melanoma, while low level solar UV exposures reduce the risk.
- Melanoma patients who receive regular sun exposures live longer than those who do not.
- UVA not only promotes skin tumor growth in mice after initiation by artificial sunlight, but also causes twice as many tumors to form .
- UVA increases melanomas in a mouse model after initiation by UVB.
- People can get considerable UVA exposure from windows, but windows do not allow passage of adequate UVB to stimulate vitamin D production.
- UVA exposure, absent UVB exposure, leads to degradation of vitamin D; and UVA also causes DNA damage.
- "High-rise office buildings, needing many large windowpanes, became increasingly popular around the mid 1910s, about 20 years prior to the first observed increase in the incidence of CMM. The time-line for the industrial revolution fits the CMM observations, unlike the introduction of fluorescent lights in the mid-1940s  or any other events that occurred after the mid- 1930s. Thus, the industrial revolution caused many workers to stay indoors during the day reducing their cutaneous vitamin D3 levels and, the UVA entering their offices caused photodegradation of vitamin D3 and mutations to the DNA of their skin cells."
"In the early 20th century, people went against evolution by going indoors during the day to work, which drastically decreased their daily amount of cutaneous vitamin D3 and, along with it, their blood levels. With the addition of larger buildings and sky scrappers, people created an unnatural UV barrier when windows were developed and used in abundance. The UV barrier created by window glass divided UVB from UVA, so that the vitamin D making UVB was excluded from our indoor working environment; only the vitamin D-breaking and DNA-mutating UVA was included. Because this unnatural UV environment existed for decades in buildings and cars, CMM began to steadily increase about 20–30 years later in the mid-1930s."In short, a boat-load of evidence that avoiding the full-spectrum UV light provided by old Sol and hiding inside drives the production of CMM. This paper shows how elegantly the theory of evolutionary adaptation can explain all of the known facts about CMM and provide the basis for uncovering the cause of a degenerative process.