Our bodies are completely reliant on oxygen for survival. The air we breathe in is not pure oxygen, but a mixture nitrogen (78.09%) and oxygen (20.95%). The approximately 1% remaining is made up of argon (0.93%), carbon dioxide (0.039% as of 2010) and other trace gases (0.003%). There is also water vapor present in the atmosphere in varying amounts depending on the locality and other factors, by up to 2%.
Oxygen is needed in our bodies to burn sugars and fatty acids to produce energy in our cells. Oxygen is brought into our lung through breathing and it is then transported by red blood cells to the rest of the body. Without a few minutes of oxygen, we will die, because our cells will stop functioning.
This is where it gets confusing. Oxygen can break down the very cells that make up our tissues and organs, our bones and even blood. It can damage DNA and critical enzymes (used for protein synthesis). It can injure and rigidify our cell membranes, making the movement of nutrients in and out of cells more harder. It could ruin our receptors for various hormones including testosterone (yep!), insulin, and thyroid.
This process of damaging the cell is similar to the way metal rusts and an apple core turns brown. The process is called oxidation or oxidative stress.
Where ever we are, the amount of oxygen in the air differs and the amount of atmosphere, and therefore air varies with elevation, so much so that even athletic track records cannot be broken at sea level, or at places with too high of an elevation due to biased oxygen levels (and air density).
In addition to the air being cleaner, I have a theory that living in a mountainous area will increase longevity due to the lower pressure experienced in the atmosphere (less oxygen). I haven't been able to find a study on this (maybe I have been looking in the wrong places).
An article in Nature (one of the most reputable journals in science), the same idea is brought forward in that the article states the following: "Oxidative stress, is intricately connected to ageing and life span." This article, however does not talk about the connection between living in a higher elevated area vs a lower elevated area and the effects on longevity.
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