Tuesday, April 27, 2010

Are tanning beds a cancer risk?

Being the scrawny white nerd that I am, I don’t tan… I burn. This concerned me greatly since I would soon be traveling to the Outer Banks in my Marine Biology class. I wanted to go swimming in the ocean, but that would mean my un-tanned, blinding white-ness would be on display. Not wanting to look completely ridiculous, I contemplated going tanning for the first time ever.

But I was worried. Tanning lotions were out because I don’t like the thought of smearing skin-altering chemicals on myself. And I had heard from many sources that tanning beds cause cancer. So I decided to look into the matter.

According to this study I found [1], exposure to tanning beds actually does increase the risk of developing malignant melanoma (skin cancer).

Where are they getting that from?

Ting and his crew wanted to test the hypothesis that increased exposure to tanning beds was linked to an increased risk of developing malignant melanoma.

To perform the study, surveys were completed by a random sample of 551 patients. The surveys asked questions like:
  1. Extent of tanning bed exposure (how much of the body was exposed to the tanning bed),
  2. use in the last 12 months (number of tanning sessions in the past year),
  3. age at first exposure,
  4. season of use (when in the year do they go tanning?),
  5. lifetime number of tanning sessions,
  6. minutes spent per session,
  7. sun protection attitudes and practices (do they usually wear sunscreen?), and
  8. leisure and occupational sun exposure (how often are they exposed to natural sunlight?).

The survey also looked at demographic information, such as:
  • Gender,
  • age,
  • race,
  • tendency to tan,
  • level of education,
  • work environment (indoor or outdoor),
  • number of sunburns in the past, and
  • previous history of various cancers.

Here is a look at the demographic information.

When doing a scientific study, you must always be wary of confounding variables (also known in statistics as a lurking variable). A confounding variable is any variable other than the independent variable that may bear any effect on the behavior of the subject being studied.
An example of a lurking variable would be testing infant memory with a matching game, but waiting too long between tests so that improved results on the second game may be due to the baby’s brain developing and not the baby’s memory. (Wikipedia)

The study took into account confounding variables such as:
  • Indoor vs. outdoor occupation and leisure activities,
  • Fitzpatrick skin type (numeric scale for skin color),
  • history of blistering sunburn, and
  • use of sunscreen and sun protective clothing.

If a patient had a family history of malignant melanoma, he was not assessed because of the potential for inaccuracy. (If their family is genetically more likely to get skin cancer without ever having used a tanning bed, than if they use tanning beds and get cancer it is impossible to determine the cause of the cancer.)

The answers to the survey were compared to those patients’ medical records. Of the 501 records available, 194 of the patients had been diagnosed with some kind of skin cancer (see Table 1).

Tables 2 and 3 below show the data that links exposure to tanning beds and risk for developing malignant melanoma.  Click on them to make them larger.

“Most modern tanning units produce mainly UV-A and less than 5% UV-B, although this amount of UV-B irradiation exceeds that in natural sunlight, and is sufficient to cause immunosuppression.” [1]

Interestingly, (according to Ting) this was the first study that accounted for confounding factors, and considered the frequency or duration of tanning bed exposure.
Yeah, that might help.

After they did a bunch of calculations that I won’t go into, they found that their hypothesis was correct. Increased exposure to tanning beds increased the risk of developing malignant melanoma.
Most of the patients that went tanning the most were young women under 45 years old, which meant that they were at the greatest risk of developing skin cancer.

Since exposure to tanning beds would increase my risk for developing cancer, I guess I better find a safer way to get a tan.
Of course, all of this is a moot point now that I’m already back from our OBX trip.
And yes, I did get sunburned after only an hour of kayaking.

Ting, W., Schultz, K., Cac, N. N., Peterson, M., & Walling, H. W. (2007). Tanning bed exposure increases the risk of malignant melanoma. International Journal of Dermatology, 46(12), 1253-1257.

DOI: 10.1111/j.1365-4632.2007.03408.x

Journal article LINK

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