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Carbon monoxide in cigarette smoke

Carbon monoxide (CO) is a clear, odorless gas that is produced by burning any carbon-based substance. So when tobacco is burned and inhaled, one of the 4,000 or more chemicals that enters the body is CO. When the smoke is inhaled into the lungs, CO is rapidly absorbed into the blood stream. CO binds to the hemoglobin in the red blood cells 200 times more effectively than oxygen does. The result is that many of these blood cells that were designed to carry oxygen to different parts of the body, instead bind to the CO, forming carboxyhemoglobin (COHb). This means that the heart has to do more work to supply the necessary amount of oxygen to the body. There is good evidence that high levels of carbon monoxide in the blood of smokers is one of the main factors causing smokers to have increased rates of cardiovascular diseases (such as angina and heart attacks). Other factors include platelet aggregation increasing the “stickiness” in the blood, stimulated by oxidant gases in cigarette smoke, and increased myocardial oxygen demand caused by nicotine. But it is clear that the reduced oxygen supply caused by carbon monoxide is a major factor. For example, increasing blood CO levels (either by smoking non-nicotine cigarettes or inhaling CO) has been shown to reduce the amount of exercize required to cause angina (chest pain) in patients with a history of angina.
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Tobacco smoking is by far the largest determinant of CO levels in the blood, with smokers typically having blood COHb levels around ten times higher than non-smokers. So the idea that you might as well smoke because there is so much pollution in the air anyway is just nonsense. See this link for a study of this in a population sample:

Decades ago the only way to measure how much smoke and CO someone had absorbed was to take a blood sample and send it to the lab for analysis. Nowadays we know that a quick and simple breath test can provide an accurate measure of CO absorption, that correlates almost perfectly with a measure of blood carboxyhemoglobin. So most smoking cessation clinics now use a CO monitor when assessing smokers to provide an estimate of how much smoke they are inhaling, and also as a way to monitor progress in treatment. At the Tobacco Dependence Clinic at UMDNJ-School of Public Health we measure exhaled CO at every appointment, just as most family doctors measure your blood pressure at every appointment. We typically find that at assessment (while still a smoker) patients have an exhaled carbon monoxide concentration of around 20 parts per million (ppm). But this can vary from just below 10 ppm to over 50 ppm for someone who has been smoking heavily recently. The good news is that when a smoker quits smoking completely, their exhaled CO levels drop to those of a non-smoker fairly quickly. When we see a patient a week after they have stopped smoking, their exhaled CO level will typically be down to zero, 1 or 2 ppm, compared to around 20 ppm at assessment . This shows that the heart is having to do less work to supply the body with necessary oxygen, and demonstrates an almost immediate improvement in health and cardiovascular risk after quitting smoking.

Medical doctors would do well to routinely measure exhaled carbon monoxide in their patients just the same way that they routinely measure blood pressure. The CO measure is a better indicator of future health outcomes and more important to get down to normal (non-smoking) levels.

A number of companies supply breath CO monitors. I’m not endorsing any of these, nor have I any financial relationships with any of them…just providing links for health professionals who may consider using a breath CO monitor in their clinical work:

For a more comprehensive description of the effects of smoking and tobacco smoke pollution on health, check out this recent paper:

Foulds J, Delnevo C, Zeidonis D, Steinberg M. Health Effects of Tobacco, Nicotine, and Exposure To Tobacco Smoke Pollution. Chapter In, Brick,J (Ed): Handbook of the Medical Consequences of Alcohol and Drug Abuse pp423-459. Haworth Press, Binghamton, NY. 2008

It can be downloaded for free from:
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About the Author

MA, MAppSci, PhD

Dr. Jonathan Foulds is an expert in the field of tobacco addiction.