Effects Of Smoking

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Harvard Medical School
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Effects Of Smoking

Tobacco Cessation
Effects Of Smoking
Effects Of Smoking
Smoking affects every part of the body, including the gastrointestinal tract. In every puff, cigarette smokers inhale over 400 toxins and 43 known carcinogens.
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Reviewed by the Faculty of Harvard Medical School

Smoking affects every part of the body, including the gastrointestinal tract. In every puff, cigarette smokers inhale over 400 toxins and 43 known carcinogens. From the lungs, these toxins have easy access to the bloodstream, which allows them to circulate throughout the body. While everyone is familiar with the links between smoking and lung cancer, emphysema and coronary artery disease, few people think about the effects of smoking on the digestive system.

Studies have shown that smokers have weaker or less frequent stomach contractions while smoking, which can cause less efficient digestion and can allow acid to accumulate, promoting acid reflux. Smoking also can cause loosening of the lower esophageal sphincter, can increase stomach acid secretion, and can reduce bicarbonate production by your pancreas (bicarbonate neutralizes your stomach acid as it enters the small intestine). Liver function also can be affected, as smoking may accelerate alcohol-induced liver disease.

Current research suggests that the effects of smoking on the gastrointestinal tract are temporary, with the exception of cancers. Most problems will reverse themselves when smoking stops. Specific disorders that are affected by smoking include:

Cancers Of The Gastrointestinal Tract

While the most publicized smoking-related cancer is lung cancer, several gastrointestinal cancers also are linked to smoking. Tobacco both initiates and promotes the development of cancer. During the very earliest stage of cancer formation, tobacco and the hundreds of toxins it produces can damage cells and cause mutations. A mutation can result in uncontrolled growth of cells, creating a cancer. Don't be fooled by people who claim to be healthy after 20 years of smoking; damage that has been done by smoking can trigger a cancer to develop after a delay of years or even decades. However, you can substantially reduce your risk of cancer if you stop smoking, and your odds for developing a cancer from past smoking diminishes with each year you are a non-smoker. Even if you do get a cancer, quitting smoking can help your chances for recovery by allowing your immune system to fight against cancer more strongly.

The strongest potential for smoking to cause gastrointestinal cancers is in the parts of the body that come into direct contact with smoke and tobacco. Cigarettes, pipes or cigars are associated with a higher risk for cancer of the mouth and esophagus. For smokeless tobacco, mouth cancer is a major risk.


Heartburn (a symptom of gastroesophageal reflux disease, or "acid reflux") is caused when acidic stomach contents flow upward into the lower part of the esophagus, which is normally protected by a muscular valve called the lower esophageal sphincter. Smoking can cause heartburn by weakening the sphincter, allowing more of the stomach's contents into the esophagus.

Peptic ulcers

Ulcers are caused by infection with Helicobacter pylori bacteria or by irritation from anti-inflammatory medications. Smoking doubles your chance of developing an ulcer of any cause, interferes with its healing, and promotes recurrences. One study found that smoking increased the risk of ulcer perforation (a hole all the way through the wall of your stomach or intestine) 10-fold among patients with ulcers.

Scientists still are investigating exactly how smoking contributes to ulcers. We know that smoking increases production of stomach acid, which acts as an irritant encouraging the development of the ulcer or delaying ulcer healing. This acid problem is compounded by a decrease in the amount of sodium bicarbonate produced by the pancreas. Normally, as acid leaves the stomach and enters the intestines, the bicarbonate neutralizes it. With greater acid levels and less bicarbonate, a duodenal ulcer is more likely to occur and less likely to heal. Even though ulcers can be treated with medications, anyone with an ulcer will be advised to quit smoking.

Liver Disease

One of the many functions of the liver is to process chemical substances such as alcohol or drugs so that they are not harmful to the body. Smoking can cause an alteration in the way the liver handles some of these substances. For example, some of the chemicals in tobacco smoke can change the speed of metabolism of some prescription drugs, making them either less effective or more toxic than they would be otherwise. Smoking is also thought to contribute to alcohol-induced liver disease.

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Last updated June 02, 2014

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