Reason Nr. 1
The first reason is something everybody knows: Fresh air is good for your lungs. Air at high altitudes is free from pollution, unlike the valleys and the cities down below. The many trees love soaking up all the CO2. Our lungs can finally take a breather from all the gases and finely divided solids. I recommend visiting the mountains as many times as possible for optimal results.
Reason Nr. 2
The second reason is less known than the first: Mountain air helps you lose weight. Without doing anything at all, just by breathing in the thin air on the mountain tops, you automatically lose weight. But why is that? The higher up you go, the less oxygen there is in the air. This means your heart must work much harder to provide your body with enough O2. This, of course, demands more energy. So, if you live your life as you did at home, and do not start eating double the amount you usually eat, the fat on your body will just melt away. Naturally, your body needs some time to adjust, so stay up there for as long and as often as possible ;)
Reason Nr. 3
The third reason is a trick athletes use. Thin air makes your body more efficient. This has to do with how our bodies transport oxygen in our blood. Anyone who paid attention in biology class in school can tell you that the transport of O2 is the red blood cells’ duty. If the air you are breathing contains less oxygen than usual, cells won’t get enough of it. Therefore, your body must adapt accordingly. This means that the amount of O2 released in the different areas of your body rises back to normal levels. If you stay up there for long enough, training and working your muscles, when you come back down you will notice something wonderful. Since the air is more saturated with oxygen, your muscles receive much more oxygen than usual for a few days. This means that they can use more energy than before, so they have more stamina. This strategy can be very useful when preparing for competition.
Reason Nr. 4
And last but not least: Air at high altitudes provides you with mental peace. The air is free from pollutants and the many different smells that can be found in any city. Instead, the only thing you can smell is the crisp air and scent of nature. Getting away from the dense air below can give you mental clarity and make you relax.
Thin air at high altitudes is obviously no miracle cure. To make a real difference you must go up a mountain more often. The more frequently you do it, the more effective it is.