UV light can affect function of DNA

[Editor-in-Chief]

UV light can affect function of DNA

Dr. Richard T. Bosshardt
Special to the Sentinel

June 25, 2006

Question: I know that too much sun exposure or use of tanning booths can be harmful and can cause skin cancer. What I don't know is how it does this. Can you explain?

Answer: The issue of how ultraviolet light affects us is, literally, a matter of life and death.

Ultraviolet (UV) light is a range of wavelengths in the electromagnetic spectrum, which includes visible light, infrared light, X-rays and gamma rays. It ranges from 1 to 380 nanometers in wavelength (a nanometer is one-billionth of a meter) and lies somewhere between visible light and X-rays.

UVA and UVB light cause the most concern medically. We are exposed to these from sunlight and from artificial sources such as tanning booths.

Both UVA and UVB can cause skin cancers, but UVB is considered the more dangerous. UVA is considered to be a major cause of the aging changes seen in our skin, especially wrinkling. In order to work well, sunblocks must block both types of UV light, but they are less effective against UVA.

UV light causes skin damage, aging, sunburns and, ultimately, skin cancer by causing damage to the cell's DNA. This is the chemical responsible for all cellular functions and cell multiplication.

The chemistry is a bit complicated, and we don't understand all of it, but in simple terms, the energy found in UV light is absorbed by the cell's DNA and "excites" the DNA molecule, somewhat like water can be brought to a boil by absorbing energy from a heat source. This excitation causes a particular molecule, thymidine, in the DNA to fuse with another thymidine molecule. This pairing disrupts the DNA chain and affects the ability of DNA to function.

Our bodies have very effective and sophisticated repair mechanisms to fix DNA. When damage occurs, a process is initiated in which the damaged segment of DNA is precisely cut out and a new, undamaged section is "spliced" into the gap. This process goes on continuously in our bodies, in uncounted millions of cells at a time, and we are oblivious to it.

How important this is can be underscored by looking at a worst-case scenario: What if our repair mechanisms failed?

We actually have a perfect example of this in medicine. It is a rare, genetic metabolic disorder called Xeroderma pigmentosa. Individuals with XP lack the necessary repair mechanisms to deal with UV damage to their cells. As a result, they are extremely sensitive to UV light.

Patients with XP develop skin cancers at a very early age -- even during infancy. Because the UV damage is cumulative, exposure causes a progressive worsening of the cell damage, and cancers arise more and more rapidly.

Every type of skin cancer is seen in XP patients, including the more uncommon, and deadly, malignant melanoma. I have seen children with XP literally covered with skin cancers of all types. They must live lives in which all unnecessary UV exposure is avoided. They can go outdoors only at night, and during the day, they must avoid even sunlight through windows. Most die at a very young age from skin cancer. There is no cure.

Patients with XP should give all of us pause before we go outdoors seeking the perfect tan or pay to lie in a tanning booth.

Richard T. Bosshardt is a plastic surgeon in Tavares. If you have a medical question, send it to him at 1879 Nightingale Lane, Suite A-2, Tavares, FL 32778 or e-mail rtbosshardt@aol.com.

Source

[beachbabe]

The DNA are damaged at 1 MED of UV exposure.
Tanning beds allow 4 MED's of exposure.