Ask the doctors: Carbon monoxide in cigarette smoke harms health

Dear Doctors: My understanding is that nicotine and tar are what hurt you when you smoke cigarettes. But you recently said there’s also carbon monoxide in cigarette smoke, and that it’s even more dangerous. Can you please explain? I want my husband to quit, and this may help.

Dear Reader: Carbon monoxide is a colorless and odorless poisonous gas. It is produced when anything that contains carbon is burned. It is often referred to simply as CO, which is its chemical formula. This indicates that each molecule consists of one carbon atom and one oxygen atom. (And for our fellow science nerds, the carbon and oxygen atoms of CO are connected by a triple bond.) The most common source of CO is the incomplete combustion of fuels such as gasoline, natural gas, heating oil, propane, kerosene, wood and charcoal. And, yes, the act of burning tobacco also releases of carbon monoxide.

What makes CO dangerous is its enormous affinity for hemoglobin. That’s the protein in red blood cells that carries oxygen from the lungs to the tissues throughout the body. A molecule of hemoglobin has four binding sites, each of which can carry a single molecule of oxygen. Due to its chemical structure, CO binds to hemoglobin 200 to 300 times more readily than oxygen. That means that when CO is present in the air someone breathes, the CO will crowd out the oxygen. This greatly diminishes the amount of oxygen the blood can carry to the cells. Even a small amount of CO can leave the cells of the body starved for oxygen.

When someone smokes a cigarette, the burning tobacco, which contains carbon, emits CO. Because the smoke is inhaled directly into the lungs, it leads to a dramatic decrease in the amount of oxygen the tissues will receive. Every time a smoker inhales, they put their body into an increasing state of oxygen debt. Among the many ill effects are breathlessness, diminished lung capacity and permanent injury to the alveoli, which are the hundreds of millions of minute air sacs in the lungs.

Exposure to CO damages the heart muscles and impairs the ability of the circulatory system to function properly. It also is linked to poor mood and cognitive impairment – and even to sexual dysfunction. Over time, the effects of tobacco use have been shown to do harm to virtually all of the tissues and metabolic functions in the body.

It has been several decades since the link between tobacco use and disease and death became clear. Yet smoking continues to be the cause of death for 480,000 Americans each year. It causes 80% to 90% of all lung cancer deaths and 80% of deaths from chronic obstructive pulmonary disease. The habit can double your risk of stroke, and it significantly increases the risk of heart attack. It is a grim way to end this column, but this is a difficult subject. We know that quitting is difficult. But the details of this discussion show that not quitting can lead to circumstances that are even more difficult.

Send your questions to askthedoctors@mednet.ucla.edu.