Most sunscreens only block UVB light, they do not block UVA. So by using sunscreen, you enable yourself to stay in the sun longer without getting burned. This increases your exposure to UVA, and it stops your body from making vitamin D from the UVB. The statistical data clearly shows an increase in the incidence of melanoma in step with the increase in sunscreen sales. And there is evidence that other cancers have higher incidence in higher economic and higher educated areas. This is thought to be due to the fact that the more money and education someone has, the more likely they are to purchase and use sunscreen as well as consciously limit sun exposure. This likely came about because it was erroneously taught in classes and magazine and newspaper articles, that sun exposure leads to melanoma and, sunscreen helps prevent it.
There are some sunscreens that block UVA waves only, but they don't do a very good job of it as they only block a small portion of the UVA spectrum. The only sunscreen that currently completely blocks UVA is zinc oxide. But zinc oxide is opaque and unsightly to most. It also blocks UVB completely as well, so you can't make vitamin D under it.
UVB creates the precursor of vitamin D from cholesterol on our skin. This precursor then gets absorbed and converted to an intermediate form of D in the liver. Then in large amounts that circulate in the blood by the kidneys and in small amounts for local use by every cell in the body, the active form of vitamin D is formed.
UVB is also what makes us get a sunburn if overexposed to it. So if a sunscreen keeps you from getting burned, it has to block UVB. UVB is good for you to the extent that it makes vitamin D for us and to the extent that vitamin D prevents cancer, especially melanoma.
There is conflicting information about where a tan comes from. According to skincancer.org, UVA is the "dominant tanning ray." And at many tanning salons, their beds have light bulbs which produce mainly UVA light waves (something like 80-90% UVA and 10-20% UVB). But according to Edward Gorham, M.P.H., Ph.D., professor at UCSD department of Family and Preventive Medicine ( http://www.ucsd.tv/search-details.aspx?showID=15770 ), it is UVB that causes tanning. From my own experience with sunscreen use, I don't tan when I use it. Also, when touring a tanning salon, I was shown a bed called a high pressure bed. It had bulbs which emitted 100% of its rays in the UVA spectrum. When I asked about its use, I was told that it will not make you tan, but once you have a tan, it will help the tan "deepen." When asked the definition of "deepen" there was no clear answer. According to the salon keeper, the "high pressure" 100% UVA bed doesn't darken the tan, it doesn't prolong the tan, and you still have to use beds with a little UVB in order to keep your tan. Hmmm.
Dr. Joseph Mercola (developer of the world's largest alternative health email newsletter) sells tanning beds for the purpose of making vitamin D. He sells one bed which produces both UVA and UVB rays, and he sells another bed which produces only UVB rays that he markets as "designed for those of you who want the benefits of the sun without tanning." Hmmm. I've emailed him asking if any of his customers have complained about this bed being "broken" because it is causing them to tan, but I haven't received an answer yet. I'm sure these answers be settled over the next few years as research on vitamin D explodes.
Dr. John B. Campise, D.C.
5035 E. Belmont #D
Fresno, CA 93727
www.campise-chiropractor-fresno.com
Henry Lim (dematologist out of Detroit, Henry Ford) has done a lot of interesting work on light, how it absorbs, causes or doesn't cause cancer, how suncreens work etc. You may want to look up some of his research. :)
ReplyDeleteMost sunscreens contain oxybenzone. It’s function is to absorb ultraviolet light, but oxybenzone can be absorbed through the skin, is linked to hormone disruption and cell damage and may lead to cancer. Be sure and read your labels!
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