It has always been stated time and again that smoking is injurious to health. The maximum harm by smoking is on the respiratory system. The effects of smoking may be understood by the effect it has upon a key enzyme in the lungs.
Monoamine oxidase A (MAOA) is important in mood regulation and breaking down compounds that help to regulate blood pressure. In a new study, researchers at the National Institute of Drug Abuse and colleagues elsewhere carried out a study using positron emission tomography (PET) scanning on a group of smokers and non-smokers.
They used a tracer chemical, which sends out signals to the scanner, to bind to MAOA and found there was less of it in the lungs of the smokers. It's possible this is linked to why people with depression, and other mental illnesses, often feel compelled to smoke. It may also contribute to the effect smoking has on blood pressure. And the lack of MAOA may even shed light on why smokers seem to run a reduced risk of Parkinson's disease. What is more, the smokers retained the tracer chemical in their bodies for much longer than the non-smokers. This suggests that maybe they respond differently to other substances entering the body, including drugs such as nicotine.
Source: Journal of Nuclear Medicine