Tuesday, July 26, 2011

The Science on Sun Exposure, Melanoma, and Sunscreen

I often sun bathe and take shirtless hikes and walks.  I rarely wear sunscreen...should I be worried about melanoma?  Should I wear sunscreen?

I'm the shirtless guy on the rock, enjoying some sun while hiking in the desert.

If I took the common dogma as truth, then the answer to both is clearly yes.  However, dogma doesn't always hold up under research.  Here are some of the studies on sun exposure, melanoma, and sunscreen:
  • Researchers at the University of New Mexico Cancer Research Center conducted a study that followed 528 people with melanoma for five years.  They found that death was inversely related to sunburns and high intermittent sun exposure.  The researchers concluded, "sun exposure is associated with increased survival from melanoma."
  • In a study of 130 Caucasian women, no association between melanoma and sunburns or proximity to the equator was found (except for women who had more than five sun burns before the age of 20).  
  • Researchers who performed a meta-analysis of 18 studies studying the effects of sunscreen on melanoma concluded that "no association was seen" between the two. 

Looking at these results, it's hard to conclude that sun exposure causes/worsens melanoma.  That would be one less reason to fear the sun.  However, why should we want to expose ourselves to the sun?

Vitamin D

UVB rays from the sun stimulate vitamin D production (when they aren't being blocked by sunscreen).  Vitamin D plays a large role in the depositing of calcium in bones, which is why it is often the first supplement recommended to those with low bone density.  It stabilizes blood levels of calcium and phosphorous.  Higher levels of vitamin D may also help prevent pancreatic cancer and improve chances of surviving from both skin and bowel cancers.  According to WebMD, deficiencies in vitamin D are associated with autoimmune diseases such as multiple sclerosis, lupus, Crohn's disease, and rheumatoid arthritis. 

My Sun Strategy

Am I saying that people should just sit in the sun all day with no concerns?  No, not at all.  It's well-established that sun burns on pale skin cause the other, less-dangerous skin cancers (basil cell and squamous cell carcinomas).  Pale skin should not be exposed to the sun for a long period of time.  Instead, gradually attaining a tan by starting with small amounts of sun will provide vitamin D while avoiding sun burns and the possible cancers that come with it.  Here's my approach for doing this:
  1. Spend time in the sun without sunscreen.  I start with 5-10 minutes when it's the first time in a while (I start with the least amount of time when I'm very fare or closer to the equator).  Desirable vitamin D hours are usually 10 A.M. to 4 P.M..
  2. I add 2-3 minutes each time I go out.
  3. If I'm outside for a prolonged period of time (at the beach with friends, playing basketball, etc.), I cover up or seek shade after reaching my time limit.  If neither is available, then I will use sunscreen (the only instance when I will use it).  

For more on the topics discussed, check out:
  1. "Is Sun Exposure a Major Cause of Melanoma?  No," by Dermatologist Sam Schuster
  2. "Scientists Reverse Stance on Sun and Cancer"
  3. "Student Who 'Hated the Sun' Died of Skin Cancer, Aged Just 21"


Floriana said...

My skin's tolerance to the sun exposure increased greatly with the improvement of my diet. I read somewhere that reducing omega-6 fatty acids makes a big difference when it comes to this.

Sean, how about darker skinned people? Would your strategy be optimal for them, too?

Dr. Sean Preuss said...

Hey Floriana,

I believe Mark Sisson advocates a better omega-3: omega-6 ratio for sun tolerance. Was it him?

Darker-skinned people can use the same strategy but start with a greater length of time.