Melanoma and UVA
Our previous blog posts discussed the role played by UVB light in inducing squamous and basal cell carcinomas via direct DNA damage. We’ve studied these mechanisms for years, but only recently have we established the link between UVA light and melanoma induction. This isn’t too surprising, since it’s difficult to distinguish UVA from UVB damage. Up until a few years ago, we assumed the UVB light was the culprit involved in all skin cancers, including melanoma.
Some clues have put us on a different track. For one thing, people who frequented tanning beds, which use UVA wavelengths of light to create tans, were found to develop high rates of melanoma. In fact indoor ultraviolet (UV) tanners are74% more likely to develop melanoma than those who have never tanned indoors.
Another clue is in the fingerprints left by UVB. Non-melanoma-type skin cancers produce 'signature mutations.' Pyrimidine dimers and 6-4 photoproducts, which commonly occur in squamous and basal cell carcinomas, are not seen in melanomas.
And finally—in vivo studies. One using Xiphophorus fish and another based on human epidemiological evidence* support the hypothesis that melanoma is caused by UVA wavelengths (320 to 400 nm), extending into the visible light spectrum at 405 nm.
Melanoma and Inflammation
The ability of UV radiation to cause tumor-initiating DNA mutations in melanocytes is now firmly established. Also crucial is inflammation’s contribution (the root cause of so many undesirable skin conditions—including wrinkles) is also crucial, and should not be overlooked in our attempts to understand melanoma. The main cause of death in people with melanoma is the spread of tumors. Studies now show that UV exposure to melanoma causes an inflammatory response that promotes the formation of distant metastasis.
What Can We Do?
Now that we know a link exists between UVA and melanoma, the prevalence of UVA is that much more of a concern. One-thousand times more prevalent than UVB, they penetrate glass and clouds and are present from sunup to sundown.
Safeguard yourself by making these few preventative steps part of your daily routine.UVA protection is more important than UVB protection. This may be still considered controversial, but I believe the ideal sunscreen has a high UVA rating and an SPF rating not exceeding 30, which indicates levels of UVB protection. Sunscreens with high UVB and low UVA protection give you a false sense of security, leading you to believe that because you're not burning you are not incurring sun damage. It’s probably better to think of sunburn as nature’s alarm system, which you turn off with high SPF sunscreens at your peril. Use anSPF 30, and if you are turning pink it’s time to get out of the sun!
Seek out products with a good UVA rating or better yet, a high zinc oxide content. The UVA-rated chemical sunscreens can be problematic. Avobenzone, which protects in the UVA range up to 400 nm by means of chemical absorption is very unstable and starts to degrade in the sun in as little as 30 minutes. It is commonly stabilized with octocrylene, but recent studies indicate that octocrylene is not only on the list of free-radical-generating chemicals we should avoid, but is also a strong allergen that can lead to contact dermatitis.
If you want to stay away from chemicals, use sunscreens containing high amounts of zinc oxide for protection up to 400 nm. And because zinc oxide is photostable, you won’t run the risk of exposing yourself to free-radical damage or allergic reactions resulting from chemical breakdown products. Another plus—zinc oxide has anti-inflammatory effects.
Modulate inflammation. News about aspirin lowering the melanoma risk for post-menopausal women has everyone talking. Taking an aspirin a day certainly can’t hurt. (If you are aspirin-sensitive, choose the low-dose buffered varieties that won’t burn your stomach.) Other anti-inflammatories like resveratrol and turmeric can also be included on your list of anti-inflammatories worth investigating.
*(Moan, J., Dahlback, A., & Setlow, R.B. (1999), Epidemiological support for a hypothesis for melanoma induction indicating a role for UVA radiation. Photochem Photobiol 70, 243-247.)
Sun Protection Tips
The two most important things to consider when protecting against deadly skin cancers are:
Ingestion: Anti-inflammatories to be taken internally.
Topical: Anti-inflammatories to be applied externally.
Epsom salts. Magnesium sulfate has mild anti-inflammatory properties and can be absorbed through the skin. Baths in Epsom salts are good for many skin conditions, including sunburn.
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