Im not expert in the matter, but from what I have read;
You die because you breathe air. Oxigen itself is a very poisonous gas,( not to mention volatile). Once you take a breathe and process air, these annoying particles called Free Radicals are a remanent of the whole process. The thing is that they are very very small, enough to go through your cell's membrane but not enough to avoid crashing against the DNA on the cell. This process over the years begin to degrade cells in your body to the point that kills them, and your tissues (heart, liver, muscle) begin to degrade.
When we are very young, our body has a nifty defense against these particles called anti-oxidants, but once we reach a certain age 25+ our production of anti-oxidants begins to diminish, leaving us open to the Free Radical bombardment, thats why Doctors encourage the consumption of foods with high levels of anti-oxidants in them.
Trees, live for hundreds of years since they don't process oxygen, in fact they exhale it, slow animals, like the turtle, tend to live for considerable amounts of time even tho they breathe oxyngen like ourselves, the difference is that their heart beats once every few minutes and they dont need to process oxygen all that often. On the other hand Mice and other animals which their heart beat to the point that it sounds like a buzzard (bzzzzzz) tend to have very little life spans since they are always on the run. There have been people that have chosen a sedentary (with healthy diet)life style and have considerably reduced the effects of aging in their bodies.
in short, every time you hold your breath, you are giving yourselves a few seconds of extra life!
