You can get garden variety health advice from the daily newspaper, the "health" section of most book stores, and of course thousands of web sites. I'm hoping to present thought provoking and maybe change provoking thoughts about individual and community health. This blog is not just what to do about health, but how to think about it. I'm looking forward to an exchange of ideas with readers. July, 2010


Tuesday, September 28, 2010

Altitude and UV Exposure

A generation of people has grown up understanding the link between sun exposure and skin cancer.  It is less understood that the relationship is complex, mediated by skin type, family history, personal history of sunburn, a weak immune system and altitude.  The theme of this posting is on the interaction of altitude with skin cancer and other risks.  By the way, about one in five of us will develop skin cancer some time in life.

From an ordinary perspective, altitude is a measure of distance above sea level.  In this context, altitude is how close something is to the sun.  Higher altitude is closer to the sun.  In addition, there is a blanket of gases and particles surrounding the earth, and it partially protects us against more severe damage from the sun’s UV radiation.  Low altitude means the atmospheric blanket is thicker, providing more protection, while higher altitude has a thinner blanket providing less protection.  Altitude differences are reflected in greater risk for skin cancer at higher altitude.  Estimates are that for every 1,000 feet of altitude above sea level, UV exposure increases by 5-10%.

Another variable is latitude.  Again, think not above sea level, but distance from the sun;  distance to the sun decreases with altitude, but also with proximity to the equator.  For example, a 10,000-foot mountaintop at the equator is closer to the sun than a similar altitude peak in a northern or southern latitude, such as Norway or New Zealand.  One group of researchers measured UV levels in high altitude Vail, Colorado, sea level in New York and in Orlando, Florida.  UV radiation was 60% more in Vail than in New York, while the farther south location of sea level Orlando had equal amounts of UV radiation as the high altitude location in Colorado.

A further complexity is climate change.  There is geological evidence that sea level was once much lower than it is now.  For example, think about the land bridge between Russia and Alaska.  At that time, people on average were able to live at a lower altitude, farther from the sun, with more atmospheric protection against UV rays.  No records exist, but based on current understandings, there would have been less skin cancer, and cellular mutations induced by UV light would have been less frequent.  This circumstance might have led to a longer life expectancy, though the effect would have been counter-balanced by the absence of medical technology, dietary gaps, and less than ideal sanitary conditions.  As climate change takes place in our own reality, average altitude will increase as seawater rises.  This predicts more skin cancer and UV related cell mutations.

These changes are imperceptible because they take place so slowly.  This reminds me of the story of the person who decided to move when he learned that most auto accidents happen within 25 miles of home.  Obviously most people will not change their residence because of UV considerations. However, there are two important take-home messages.  Sun protection is always important, but increasingly so at higher altitude or closer distance to the equator.  The second is that climate change is not just a concern for polar bear habitat. It presents serious threats for our life on planet Earth.

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