Smoking and Your Digestive System

Cigarette smoking causes a variety of life-threatening diseases, including lung cancer, emphysema, and heart disease. An estimated 400,000 deaths each year are caused directly by cigarette smoking.

Smoking is responsible for changes in all parts of the body, including the digestive system. This fact can have serious consequences because it is the digestive system that converts foods into the nutrients the body needs to live.

Current estimates indicate that about one-third of all adults smoke. And, while adult men seem to be smoking less, women and teenagers of both sexes seem to be smoking more. How does smoking affect the digestive system of all these people?

Harmful Effects of Smoking on Digestive System

Smoking has been shown to have harmful effects on all parts of the digestive system, contributing to such common disorders as heartburn and peptic ulcers. The effects of smoking on the liver often are not discussed, but studies show that smoking may alter the way in which the liver handles drugs and alcohol. In addition, smoking apparently changes the way in which food is processed by the body. In fact, there seems to be enough evidence to stop smoking solely on the basis of digestive distress.

Smoking Contributes to Heartburn

Heartburn is a very common disorder among Americans. Heartburn is especially common among pregnant women, with 25% reporting daily heartburn and more than 50% experiencing occasional distress.

Most people will experience heartburn if the lining of the esophagus comes into contact with too much stomach juice for a long period of time. This stomach juice consists of acid produced by the stomach, as well as bile salts and digestive enzymes that may have washed into the stomach from the intestine.

Normally, a muscular valve at the lower end of the esophagus, the lower esophageal sphincter (LES), keeps the acid solution in the stomach and out of the esophagus. Sometimes the LES is weak and allows stomach juice to reflux, or flow backward into the esophagus.

Many people have occasional reflux episodes. Persons with heartburn usually have frequent episodes or fail to return the refluxed material to the stomach promptly. The prolonged contact of acid stomach juice with the esophageal lining injures the esophagus and produces burning pain. Smoking decreases the strength of the esophageal valve, thereby allowing more refluxed material into the esophagus.

Smoking also seems to promote the movement of bile salts from the intestine to the stomach to produce a more harmful reflux material. Finally, smoking may directly injure the esophagus, making it less able to resist further damage because of contact with refluxed material from the stomach.

Does Smoking Cause Peptic Ulcers?

An ulcer is an open sore in the lining of the stomach or duodenum, the first part of the small intestine. The exact cause of ulcers is not known. A relationship between smoking cigarettes and ulcers, especially duo- denal ulcers, does exist. The 1989 Surgeon General’s report stated that ulcers are more likely to occur, less likely to heal, and more likely to cause death in smokers than nonsmokers.

Why is this so? Doctors are not really sure, but smoking does seem to be one of several factors that work together to promote the formation of ulcers.

Stomach acid is important in producing ulcers. Normally, most of this acid is buffered by the food we eat. Most of the unbuffered acid that enters the duodenum is quickly neutralized by sodium bicarbonate, a naturally occurring alkali produced by the pancreas. Some studies show that smoking reduces the bicarbonate produced by the pancreas, interfering with the neutralization of acid in the duodenum. Other studies suggest that chronic cigarette smoking may increase the amount of acid secreted by the stomach.

There also is some evidence suggesting that smoking increases the speed at which the stomach empties its acid contents into the small intestine. Although the evidence is inconclusive on some of these issues, all are possible explanations for higher rate and slower healing of ulcers among smokers.

Whatever causes the link between smoking and ulcers, two points have been repeatedly demonstrated: Persons who smoke are more likely to develop an ulcer, especially a duodenal ulcer, and ulcers are less likely to heal quickly among smokers in response to otherwise effective treatment. This research tracing the relationship between smoking and ulcers strongly suggests that a person with an ulcer should stop smoking.

How Does Smoking Affect the Liver?

The liver is a very important organ that has many tasks. Among other things, the liver is responsible for processing drugs, alcohol, and other toxins to remove them from the body. There is evidence that smoking alters the ability of the liver to handle these substances. In some cases, this may influence the dose of medication necessary to treat an illness. One theory, based on current evidence, also suggests that smoking can aggravate the course of liver disease caused by excessive alcohol intake.

Does Smoking Help Control Weight?

A common belief is that smoking helps to control weight. Smokers do, indeed, weigh less, on average, than nonsmokers. And those who quit smoking are more likely to gain weight. Most people think this is because smokers eat less than nonsmokers.

Some researchers have found, however, that smokers actually eat more than nonsmokers. How can they weigh less? What happens to the extra calories? Scientist are not really sure about the answers to these questions, but they caution smokers not to think that just because they weigh less, they are healthier than if they didn’t smoke. Research shows that the bodies of smokers use food less efficiently than nonsmokers. Scientists are still studying what implications this has on the long-range health of smokers.

Can Damage to Digestive System Be Reversed?

Some of the effects of smoking on the digestive system appear to be of short duration. For example, the effect of smoking on bicarbonate production by the pancreas does not appear to last. Within a half-hour after smoking, the production of bicarbonate returns to normal. The effects of smoking on how the liver handles drugs also disappear when a person stops smoking. While doctors suspect that most other digestive abnormalities caused by smoking would also disappear soon after stopping smoking, this question has received little study.


While all the evidence is not yet available, it seems clear that smoking cigarettes plays an important role in causing some digestive diseases. The relationship between heartburn and smoking is very clear. The link between smoking and ulcers, seems indisputable. Studies showing that cigarettes affect the way the liver processes drugs, alcohol, and other substances suggest more problems for smokers.

Not all the effects of smoking on the digestive system are understood clearly. However, the evidence that is available makes a powerful statement that smoking is bad for digestive health.

From Your Physician

“A Guide for Patients” is being given to you by your physician to help you better understand the particular digestive problem affecting you. Studies have shown that the more that a patient knows, the easier it is for the patient to cooperate with the physician and the more effective can be the prescribed treatment.

The information in “A Guide for Patients” has been prepared by the National Digestive Diseases Information Clearinghouse, a service of the National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, U.S. Public Health Service.