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Health effects of tobacco

Tobacco products, especially when smoked or used orally, have serious negative effects on human health.[1][2] Smoking and smokeless tobacco use is the single greatest cause of preventable death globally.[3] As many as half of people who smoke tobacco or use it orally die from complications related to such use.[4] It has been estimated that each year, in total about 6 million people die from tobacco-related causes (about 10% of all deaths), with 600,000 of these occurring in non-smokers due to secondhand smoke.[4][5] It is further estimated to have caused 100 million deaths in the 20th century.[4]

"Health effects of smoking" and "Dangers of smoking" redirect here. For cannabis, see Effects of cannabis. For smoking crack cocaine, see Crack cocaine § Health issues.

Tobacco smoke contains over 70 chemicals that cause cancer.[4][6] It also contains nicotine, a highly addictive psychoactive drug. When tobacco is smoked, the nicotine in it causes physical and psychological dependency. Cigarettes sold in underdeveloped countries have higher tar content. They are less likely to be filtered, increasing vulnerability to tobacco smoking–related diseases in these regions.[7]


Tobacco use most commonly leads to diseases affecting the heart, liver and lungs. Smoking is a major risk factor for several conditions, namely pneumonia, heart attacks, strokes, chronic obstructive pulmonary disease (COPD) (including emphysema and chronic bronchitis), and multiple cancers (particularly lung cancer, cancers of the larynx and mouth, bladder cancer, and pancreatic cancer). It is also responsible for peripheral arterial disease and high blood pressure. The effects vary, depending on how frequently and for how many years a person smokes. Smoking earlier in life and smoking cigarettes higher in tar increase the risk of these diseases. Additionally, environmental tobacco smoke, or second-hand smoke, has manifested harmful health effects in people of all ages.[8] Tobacco use is also a significant factor in miscarriages among pregnant smokers. It contributes to a number of other health problems of the fetus such as premature birth, low birth weight, and increases the chance of sudden infant death syndrome (SIDS) by 1.4 to 3 times.[9] Incidence of erectile dysfunction is approximately 85 percent higher in male smokers compared to non-smokers.[10][11]


Many countries have taken measures to control the consumption of tobacco (smoking) by restricting its usage and sales. On top of that, they have printed warning messages on packaging. Moreover, smoke-free laws that ban smoking in public places like workplaces, theaters, bars, and restaurants have been enacted to reduce exposure to second-hand smoke.[4] Tobacco taxes inflating the price of tobacco products have also been imposed.[4]


In the late 1700s and the 1800s, the idea that tobacco use caused certain diseases, including mouth cancers, was initially accepted by the medical community.[12] In the 1880s, automation dramatically reduced the cost of cigarettes, cigarette companies greatly increased their marketing, and use expanded.[13][14] From the 1890s onwards, associations of tobacco use with cancers and vascular disease were regularly reported. By the 1930s multiple researchers concluded that tobacco use caused cancer and tobacco users lived substantially shorter lives.[15][16] Further studies were published in Nazi Germany in 1939 and 1943, and one in the Netherlands in 1948. However, the widespread attention was first drawn in 1950 by researchers from the US and UK but their research were widely criticized. Follow-up studies in the early 1950s found that smokers died faster and were more likely to die of lung cancer and cardiovascular disease.[12] These results were accepted in the medical community and publicized among the general public in the mid-1960s.[12]

Share of deaths from smoking, 2017[46]

Share of deaths from smoking, 2017[46]

The number of deaths attributed to smoking per 100,000 people in 2017[47]

The number of deaths attributed to smoking per 100,000 people in 2017[47]

are tar components produced by pyrolysis in smoldering organic matter and emitted into smoke. Several of these PAH's are already toxic in their normal form, however, many of then can become more toxic to the liver. Due to the hydrophobic nature of PAH's they do not dissolve in water and are hard to expel from the body. In order to make the PAH more soluble in water, the liver creates an enzyme called Cytochrome P450 which adds an additional oxygen to the PAH, turning it into a mutagenic epoxides, which is more soluble, but also more reactive.[217] The first PAH to be identified as a carcinogen in tobacco smoke was benzopyrene, which been shown to toxicate into a diol epoxide and then permanently attach to nuclear DNA, which may either kill the cell or cause a genetic mutation. The DNA contains the information on how the cell function; in practice, it contains the recipes for protein synthesis. If the mutation inhibits programmed cell death, the cell can survive to become a cancer, a cell that does not function like a normal cell. The carcinogenicity is radiomimetic, i.e. similar to that produced by ionizing nuclear radiation. Tobacco manufacturers have experimented with combustion less vaporizer technology to allow cigarettes to be consumed without the formation of carcinogenic benzopyrenes.[218] Although such products have become increasingly popular, they still represent a very small fraction of the market, and no conclusive evidence has shown to prove or disprove the positive health claims.

Polycyclic aromatic hydrocarbons

is a pyrolysis product that is abundant in cigarette smoke. It gives smoke an acrid smell and an irritating, tear causing effect and is a major contributor to its carcinogenicity. Like PAH metabolites, acrolein is also an electrophilic alkylating agent and permanently binds to the DNA base guanine, by a conjugate addition followed by cyclization into a hemiaminal. The acrolein-guanine adduct induces mutations during DNA copying and thus causes cancers in a manner similar to PAHs. However, acrolein is 1000 times more abundant than PAHs in cigarette smoke and is able to react as is, without metabolic activation. Acrolein has been shown to be a mutagen and carcinogen in human cells. The carcinogenicity of acrolein has been difficult to study by animal experimentation, because it has such a toxicity that it tends to kill the animals before they develop cancer.[215] Generally, compounds able to react by conjugate addition as electrophiles (so-called Michael acceptors after Michael reaction) are toxic and carcinogenic, because they can permanently alkylate DNA, similarly to mustard gas or aflatoxin. Acrolein is only one of them present in cigarette smoke; for example, crotonaldehyde has been found in cigarette smoke.[219] Michael acceptors also contribute to the chronic inflammation present in diseases brought about by smoking.[86]

Acrolein

are a group of carcinogenic compounds found in cigarette smoke but not in uncured tobacco leaves. Nitrosamines form on flue-cured tobacco leaves during the curing process through a chemical reaction between nicotine and other compounds contained in the uncured leaf and various oxides of nitrogen found in all combustion gasses. Switching to Indirect fire curing has been shown to reduce nitrosamine levels to less than 0.1 parts per million.[220][221]

Nitrosamines

Average price of a pack of 20 cigarettes, measured in international dollars in 2014[283]

Average price of a pack of 20 cigarettes, measured in international dollars in 2014.

Taxes as a share of cigarette price, 2014[284]

Taxes as a share of cigarette price, 2014[284]

Types of bans on tobacco advertising, 2014[285]

Types of bans on tobacco advertising, 2014[285]

Support to help quit tobacco use, 2014[286]

Support to help quit tobacco use, 2014[286]

Education and counselling by physicians of children and adolescents have been found to be effective in decreasing tobacco use.[281] The World Health Organization (WHO) estimates that 5.6 billion people, or 71% of the world's population, are protected by at least one tobacco prevention policy.[282]

History[edit]

Pre-cigarette[edit]

Texts on the harmful effects of smoking tobacco were recorded in the Timbuktu manuscripts.[302]


James I wrote a book that denounced tobacco smoking as: "...loathsome to the eye, hateful to the nose, harmful to the brain, dangerous to the lungs..."[303]


Pipe smoking gradually became generally accepted as a cause of mouth cancers following work done in the 1700s. "An association between a variety of cancers and tobacco use was repeatedly observed from the late 1800s into the early 1920s."[304]


Gideon Lincecum, an American naturalist and practitioner of botanical medicine, wrote in the early 19th century on tobacco: "This poisonous plant has been used a great deal as a medicine by the old school faculty, and thousands have been slain by it. ... It is a very dangerous article, and use it as you will, it always diminishes the vital energies in exact proportion to the quantity used – it may be slowly, but it is very sure."[305]


The 1880s invention of automated cigarette-making machinery in the American South made it possible to mass-produce cigarettes at low cost, and smoking became common. This led to a backlash and a tobacco prohibition movement, which challenged tobacco use as harmful and brought about some bans on tobacco sale and use.[13] In 1912, American Dr. Isaac Adler was the first to strongly suggest that lung cancer is related to smoking.[306] In 1924, economist Irving Fisher wrote an anti-smoking article for Reader's Digest which said "...tobacco lowers the whole tone of the body and decreases its vital power and resistance ... tobacco acts like a narcotic poison, like opium, and like alcohol, though usually in a less degree".[307] In December 1952, the Reader's Digest reprinted an article titled Cancer by the Carton which outlined the research links between smoking and lung cancer.


Prior to World War I, lung cancer was considered to be a rare disease, which most physicians would never see during their career.[308][309] With the postwar rise in popularity of cigarette smoking, however, came an epidemic of lung cancer.[310][311] For instance, it is estimated that "35 to 79 percent of excess veteran deaths due to heart disease and lung cancer are attributable to military-induced smoking"[312]

Early observational studies[edit]

From the 1890s onwards, associations of tobacco use with cancers and vascular disease were regularly reported.[12] In 1930, Fritz Lickint of Dresden, Germany, published[16][15] a meta-analysis citing 167 other works to link tobacco use to lung cancer.[15] Lickint showed that people with lung cancer were likely to be smokers. He also argued that smoking tobacco was the best way to explain the fact that lung cancer struck men four or five times more often than women (since women smoked much less),[16] and discussed the causal effect of smoking on cancers of the liver and bladder.[15]

E. Cuyler Hammond

List of cigarette smoke carcinogens

Health effects of electronic cigarettes

Tobacco Free awareness action – How many people smoke in cars