Wednesday, May 5, 2010
Melanoma Not Caused by Early Ultraviolet (UVA) Light Exposure, New Fish Experiments Show
(I'm posting this article until someone else has a post they want to put up. Please feel free to replace it.)
"UVA exposure is unlikely to have contributed to the rise in the incidence of melanoma over the past 30 years, the researchers conclude, because the fish model had been the only animal model to indicate a connection between exposure to UVA at a young age and later development of melanoma". (The 1993 experiment could not be replicated in mammalian models of melanoma)
Our data refute the only direct evidence that UVA causes melanoma, which is not to say that UVA is harmless....... UVA is just not as dangerous as we thought because it doesn't cause melanoma....
UVA is a carcinogen responsible for squamous cell carcinomas that also causes premature aging of the skin and suppresses the immune system. It's also possible, the authors note, that long-term chronic exposure to UVA can hasten the progression to malignancy of melanocytes in the skin that are already on the path to becoming melanoma.
The thought was that people who used sunscreen stayed out in the sun longer, absorbing a higher dose of UVA, causing a higher risk for melanoma" Mitchell said. Most sunscreens now protect against UVA. However, the increase in the incidence of melanoma has been thought to be partly attributable to childhood exposure to UVA back when sunscreens blocked only UVB. That's unlikely, given the new results...
UVB exposure damages DNA directly, while UVA is thought to inflict its damage indirectly by inducing melanin free radicals that react with DNA to form oxidative damage that leads to melanoma. Previous studies had shown a correlation between melanin radical formation and melanoma in the UVA range of the solar spectrum. Since Mitchell and colleagues found no connection between UVA and melanoma, they note that the role of melanin free radicals in this disease is brought into question." http://www.sciencedaily.com/releases/2010/05/100504155419.htm
Posted by Chloe at 3:13 PM