Tobacco

The term tobacco refers to plants of the genus Nicotiana, which may be consumed in various ways. Because cigarette smoking is the predominant method of tobacco consumption in the United States, in public health the term tobacco use is often used as a synonym for cigarette smoking without consideration of the different modes of tobacco consumption and differing health risks posed by them. This entry describes the health risks associated with cigarette smoking, other tobacco smoking, and environmental tobacco smoke (ETS) and contrasts these to the effect of nicotine in itself and to the use of smokeless tobacco (σT). It also explores the importance of tobacco research in the history of epidemiology and the potential of epidemiological studies in reducing the health impacts of smoking.

Tobacco is native to the Americas, where it was cultivated by indigenous populations from about 4000 BCE and used in smoked and smokeless forms, largely for ceremonial purposes. Less than 100 years after its discovery by European explorers around AD 1500, tobacco was being used throughout the world, a testimony to the powerful psychoactive properties it delivers to human brains. Cigarette smoking started to become popular only around 1900 with the introduction of efficient mass production and wide distribution of cigarettes during the 20th century's two world wars made it the dominant form of tobacco use globally.

Ochsner and DeBakey recognized a link between smoking and lung cancer as early as 1939. Schairer and Scho¨niger (1943) published one of the first epidemiologic studies of this relationship, in German, during World War II (it was not widely distributed or indexed at the time, but was resurrected in English in 2001). But it was not until the studies of cigarette smoking and lung cancer by Doll and Hill (1950), Wynder and Graham (1950), and others a half century ago that the dangers of smoking were clearly established. While difficult to imagine today, the medical community that then dominated public health was sufficiently conservative that these results were not immediately accepted despite previous evidence. These early studies of the relationship between smoking and health risks also played an important role in establishing the merits of observational epidemiologic studies.

Today, it is well established that regular moderate or heavy cigarette smoking (and to a lesser extent, smoking of tobacco in other forms) causes wellknown morbidity and mortality risks, with total attributable risk far exceeding that from any other voluntary exposure in wealthy countries. Cigarette smoke also creates an environmental exposure, labeled ‘second-hand smoke’ or ‘environmental tobacco smoke’ (ETS). Because smoking has been so prevalent for so long and causes high relative risks for many diseases, and because it offers little opportunity for experimental intervention, smoking stands as a near-perfect demonstration of what can be done with observational epidemiology (though perhaps also as a rarely attainable archetype).

In contrast, nicotine, the primary reason people smoke or otherwise use tobacco, is a relatively benign [Page 1039]mild stimulant, similar to caffeine. Nicotine causes transient changes in cardiovascular physiology, as do many mild stimulants that might cause a small risk of cardiovascular disease. There is general agreement that nicotine is addictive for many people (the term addictive is not well-defined, but nicotine consumption fits most proposed definitions, at least for a portion of the population). But nicotine by itself does not appear to cause a substantial risk of any life-threatening disease; the epidemiologic evidence on nicotine in the absence of smoking is sufficiently limited that it is impossible to distinguish small risks from zero risk. Although not extensively studied, research suggests that nicotine may have psychological and neurological health benefits, protecting against Parkinson's disease and possibly dementia, and providing acute relief from schizophrenia and other psychological morbidities.

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