According to the National Cancer Institute, approximately 87 percent of lung cancer deaths are caused by smoking cigarettes. The most active ingredient in cigarettes is nicotine. Nicotine is an alkaloid substance that is naturally found in the tobacco plant. In small doses the substance has addictive side effects, while in large doses it can quickly become toxic to the body. Regardless of the dose, nicotine can affect the lungs both directly and indirectly.
According to the American Heart Association, nicotine can directly affect the lungs through the blood stream. When nicotine enters the bloodstream through the lungs, blood pressure is temporarily increased, and the arteries throughout the body become more narrow. This restricts the amount of blood that can be circulated throughout the body. Restriction of blood also restricts the amount of oxygen the lungs can circulate in the blood to keep the body healthy. To further complicate the situation, the carbon monoxide that usually accompanies nicotine restricts the amount of oxygen the blood can carry. This causes a shortage between the amount of oxygen the body needs and the amount of oxygen the lungs can place in the bloodstream.
Though nicotine does not directly cause lung cancer, once cancer has formed in the lungs, continued exposure to nicotine can speed up the growth of lung cancer cells. According to Piyali Dasgupta, PhD, from the H. Lee Moffitt Cancer Center, tumors exposed to nicotine through smoking or tobacco substitutes can contribute to the growth and progression of tumors. It does so by plugging into nicotine receptors in the lung cells called nicotinic acetylcholine receptors. By doing this, nicotine can dramatically increase the working mechanisms of the cell.
Most of nicotine's effects on the lungs is not caused by the nicotine itself but by the addictive effect that the substance has on the body. Once inhaled, nicotine-containing cigarette smoke has an immediate effect on the body's reward system of the brain, causing an addiction to form. When tobacco is chewed or smoked, it is not so much the nicotine that is harmful to the lungs as it is the many other toxic chemicals that are ingested along with the nicotine. These chemicals have the ability to damage and alter the cell structure of the lung tissue. One of the most common cell alterations that can occur is cancer.