Tobacco

Overview
Tobacco is an agricultural product processed from the fresh leaves of plants in the genus Nicotiana.

Tobacco has been growing on the American Continent since about 6000 BC and began being used by native cultures at about 3000 BC. It has been smoked in one form or another since about 2000 BC. There are pictoral drawings of ancient Mayans smoking crude cigars from 1400 BC. Tobacco has a very long history of use in Native American culture and played an important part in the foundation of the United States of America, going back to colonial times and the original Jamestown settlement.

Commercially available dried, cured and natural forms, it is often smoked (see tobacco smoking) in the form of a cigar or cigarette, or in a stem pipe, water pipe, or hookah. Tobacco can also be chewed, "dipped" (placed between the cheek and gum), or sniffed into the nose as finely powdered snuff. Many countries set a minimum smoking age, regulating the purchase and use of tobacco products.

All methods of tobacco consumption results in varying quantities of nicotine being absorbed into the user's bloodstream. Over time, tolerance and dependence develop. Absorption quantity, frequency, and speed seem to have a direct relationship with how strong a dependence and tolerance, if any, might be created.

Health effects
All means of tobacco consumption result in the absorption of nicotine, in varying amounts, into the user's bloodstream. A lethal dose of nicotine is contained in as little as one half of a cigar or three cigarettes. However, only a small fraction of the nicotine contained in these products is actually released into the smoke: most clinically significant cases of nicotine poisoning result from concentrated forms of the compound used as insecticides. Some sources report, however, that even a discarded cigarette butt can contain enough nicotine to kill a small child. Other active alkaloids in tobacco include harmala alkaloids.

Long-term tobacco use carries significant risks of developing various cancers as well as strokes and severe cardiovascular and respiratory diseases. Significantly shorter life expectancies have been associated with tobacco smoking. It has been shown that tobacco may cause lasting brain changes just like morphine or cocaine.

Many jurisdictions have enacted smoking bans in an effort to minimize possible damage to public health caused by tobacco smoking. The substantially increased risk of developing cancer as a result of tobacco usage seems to be due to the plethora of nitrosamines and other carcinogenic compounds found in tobacco and its residue as a result of anaerobic heating, either due to smoking or to flue-curing or fire-curing. The use of flue-cured or fire-cured smokeless tobacco in lieu of smoked tobacco reduces the risk of respiratory cancers but still carries significant risk of oral cancer. In contrast, use of steam-cured chewing tobacco (snus) avoids the carcinogenicity by not generating nitrosamines, though the negative effects of the nicotine on the cardiovascular system and pancreas are not ameliorated. More than 400,000 Americans a year die from smoking: 276,000 men and 142,000 women.

One study from the Aristotle University of Thessaloniki in Greece measured the amount of naturally occurring radium and polonium found in Greece's tobacco leaves. The radiation dose was discovered to be nearly a thousand times more than the amount of Caesium-137 found in the leaves of plant life adjacent to the Chernobyl disaster. Despite the actual radiation dose attained by tobacco smokers being only 10 percent of the mean dose any person receives from the environment, some scientists believe that this radioactive content is a major cause of cancer deaths in smokers, and not nicotine or tar.