There is still great discussion about how cigarettes adversely affect human beings. There is no question that smokers are prone to many diseases only rarely seen in non-smokers. It is very likely that no specific factor in cigarette smoke causes disease all by itself, but that multiple factors produce the conditions under which disease can begin. Smoking has been strongly implicated in bronchitis and emphysema, lung cancer, oral and laryngeal cancer, heart disease and peripheral vascular disease. All of these conditions are seen in nonsmokers, but large population studies demonstrate a much higher incidence in smokers.
In addition to the circumstantial evidence correlating a greater incidence of many diseases with smoking, there has been varied research on the biological effects of tobacco smoke on animals and humans. Some of these direct effects of tobacco smoke suggest its capacity for producing disease in the smoker. Smoking lowers skin temperature, often by several degrees, principally trough the constricting effect of nicotine on blood vessels. Carbon monoxide levels rise in the blood when a person is smoking. The ability to expel air rapidly from the lungs is somewhat impaired even by a single cigarette. Adverse changes in the activity of several important chemicals in the body can be demonstrated after smoking. All these effects of smoking and the many others known, are difficult to interpret as conclusive evidence that disease results as a direct consequence. But the changes are certainly disturbing.
The principle arguments of the tobacco manufacturers and cigarette supporters have been that the population studies produce only circumstantial evidence and that the demonstrable biological effects do not necessarily produce disease. They also point out that no single ingredient in tobacco smoke can be shown to produce cancer, despite many attempts. But the thousands of physicians who have quit smoking in the last few years do not need absolute cause and effect proof. Nor are they blind to the fact that tobacco smoke may create conditions under which these diseases are more readily apt to develop.
The number of cigarettes an individual smokes is one of the determinants of eventual damage, although individual susceptibility is also important. If a person smokes one pack a day for one year or two packs a day for one year, he has smoked two pack years and so on. Calculating by pack years it appears that 40 pack years is a crucial time period above which the incidence of cancer of the lung, emphysema, and other serious consequences rises rapidly.
In addition to the circumstantial evidence correlating a greater incidence of many diseases with smoking, there has been varied research on the biological effects of tobacco smoke on animals and humans. Some of these direct effects of tobacco smoke suggest its capacity for producing disease in the smoker. Smoking lowers skin temperature, often by several degrees, principally trough the constricting effect of nicotine on blood vessels. Carbon monoxide levels rise in the blood when a person is smoking. The ability to expel air rapidly from the lungs is somewhat impaired even by a single cigarette. Adverse changes in the activity of several important chemicals in the body can be demonstrated after smoking. All these effects of smoking and the many others known, are difficult to interpret as conclusive evidence that disease results as a direct consequence. But the changes are certainly disturbing.
The principle arguments of the tobacco manufacturers and cigarette supporters have been that the population studies produce only circumstantial evidence and that the demonstrable biological effects do not necessarily produce disease. They also point out that no single ingredient in tobacco smoke can be shown to produce cancer, despite many attempts. But the thousands of physicians who have quit smoking in the last few years do not need absolute cause and effect proof. Nor are they blind to the fact that tobacco smoke may create conditions under which these diseases are more readily apt to develop.
The number of cigarettes an individual smokes is one of the determinants of eventual damage, although individual susceptibility is also important. If a person smokes one pack a day for one year or two packs a day for one year, he has smoked two pack years and so on. Calculating by pack years it appears that 40 pack years is a crucial time period above which the incidence of cancer of the lung, emphysema, and other serious consequences rises rapidly.
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