Sedentary lifestyle, smoking and air pollution decrease our ability to ingest and process oxygen, while, at the same time, stress and unhealthy food habits actually increase the body's oxygen requirement.
We end up with a deadend: as you lead a lifestyle that is not healthy enough, you become less able to admit oxygen, which makes you even less healthy and thus provokes an oxygen craving you cannot quite satisfy because… well, you get the idea.
All in all, it may lead to a number of impairments typical for the 21st century, such as mental and physical fatigue, premature aging, and others.