Chapter 395

The use of tobacco leaf to create and satisfy nicotine addiction was introduced to Columbus by Native Americans and spread rapidly to Europe. Use of tobacco as cigarettes, however, only became popular in the twentieth century and so is a modern phenomenon, as is the epidemic of disease caused by this form of tobacco use.

Nicotine is the principal constituent of tobacco responsible for its addictive character, but other smoke constituents and behavioral associations contribute to the strength of the addiction. Addicted smokers regulate their nicotine intake by adjusting the frequency and intensity of their tobacco use both to obtain the desired psychoactive effects and avoid withdrawal.

Unburned cured tobacco used orally contains nicotine, carcinogens, and other toxicants capable of causing gum disease, oral and pancreatic cancers, and an increase in the risk of heart disease. When tobacco is burned, the resultant smoke contains, in addition to nicotine, more than 4000 other compounds that result from volatilization, pyrolysis, and pyrosynthesis of tobacco and various chemical additives used in making different tobacco products. The smoke is composed of a fine aerosol and a vapor phase; aerosolized particles are of a size range that results in deposition in the airways and alveolar surfaces of the lungs. The aggregate of particulate matter, after subtracting nicotine and moisture, is referred to as tar.

The alkaline pH of smoke from blends of tobacco utilized for pipes and cigars allows sufficient absorption of nicotine across the oral mucosa to satisfy the smoker's need for this drug. Therefore, smokers of pipes and cigars tend not to inhale the smoke into the lung, confining the toxic and carcinogenic exposure (and the increased rates of disease) largely to the upper airway for most users of these products. The acidic pH of smoke generated by the tobacco used in cigarettes dramatically reduces absorption of nicotine in the mouth, necessitating inhalation of the smoke into the larger surface of the lungs in order to absorb quantities of nicotine sufficient to satisfy the smoker's addiction. The shift to using tobacco as cigarettes, with resultant increased deposition of smoke in the lung, has created the epidemic of heart disease, lung disease, and lung cancer that dominates the current disease manifestations of tobacco use.

Several genes have been associated with nicotine addiction. Some reduce the clearance of nicotine, and others have been associated with an increased likelihood of becoming dependent on tobacco and other drugs as well as a higher incidence of depression. Rates of smoking cessation have increased, and rates of nicotine addiction have decreased dramatically, since the mid-1950s, suggesting that factors other than genetics are important. It is likely that genetic susceptibility can influence the probability that adolescent experimentation with tobacco will lead to addiction as an adult.

Adult cigarette smoking prevalence has declined to about 20% in the United States, with similar declines in Canada and most European countries. Male smoking prevalence is ...

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