Heartburn is a symptom of gastroesophageal reflux disease (GERD), which is a digestive disorder that affects the lower esophageal sphincter (LES) - the muscle connecting the esophagus with the stomach. Many people, often pregnant women, suffer from heartburn or acid indigestion caused by GERD. Some doctors believe that some people suffer from GERD due to a condition called hiatal hernia. In most cases, heartburn can be relieved through diet and lifestyle changes; however, some people may require medication or surgery. Up to 15 million Americans experience heartburn daily. Some studies have reported that 36% to 44% of adults experience heartburn at least once per month, 14% every week, and 7% once a day. Gastroesophageal reflux disease itself is common. One study reported that 20% of people had frequent symptoms of GERD but that very few of them sought help for the condition. People at all ages are susceptible to GERD. Elderly people with GERD tend to have a more serious condition than younger people with the problem.

Pregnant women are particularly vulnerable to GERD in their third trimester as the growing uterus puts increasing pressure on the stomach. Heartburn in such cases is often resistant to dietary interventions and even antacids.

In normal digestion, the LES opens to allow food to pass into the stomach and closes to prevent food and acidic stomach juices from flowing back into the esophagus. Gastroesophageal reflux occurs when the LES is weak or relaxes inappropriately allowing the stomach's contents to flow up into the esophagus.

Unlike the lining of the stomach, which has a thin layer of protective mucus, the lining of the esophagus offers only a weak defense against stomach acid and other harmful substances. The most important structure in protecting the esophagus is the LES but if, in spite of LES pressure, there is some acid back-up (reflux), an additional defense mechanism, the peristaltic action of the esophagus, pushes the residue back down into the stomach.

If the LES or the peristaltic action is impaired, stomach tone is increased or other protective mechanisms fail, then acid and other substances back up into the esophagus from the stomach, causing GERD. The most common symptoms of GERD are heartburn (a burning sensation in the chest and throat) and regurgitation (a sensation of acid backed up in the esophagus). In most people, the symptoms are short-lived and occur infrequently. In about 20% of cases, however, the condition becomes chronic. In such cases, the acid can cause irritation, inflammation, and even erosion of the esophagus (a condition called esophagitis). Although acid is a primary factor in damage caused by GERD, other products of the digestive tract, including pepsin and bile, can also be harmful.

In some cases the esophagus may be hypersensitive. When irritants are introduced into the esophagus, the immune system reacts with an exaggerated (hyperreactive) response to them, triggering the release of agents that cause inflammation and possibly injury. This event is similar to the asthmatic response to irritants in the airways.

The severity of GERD depends on tissue sensitivity, LES dysfunction, the type and amount of fluid brought up from the stomach and the neutralizing effect of saliva. Some doctors believe a hiatal hernia may weaken the LES and cause reflux. Recent studies show that the opening in the diaphragm acts as an additional sphincter around the lower end of the esophagus. Studies also show that hiatal hernia results in retention of acid and other contents above this opening. These substances can reflux easily into the esophagus.

Dietary and lifestyle choices may contribute to GERD. Certain foods and beverages, including chocolate, peppermint, spearmint, fried or fatty foods, coffee, garlic, onions or alcoholic beverages, may weaken the LES or increase stomach tone causing reflux and heartburn. Caffeinated drinks and decaffeinated coffee increase acid content in the stomach. Other acidic foods include citrus and tomato products. All carbonated beverages increase the risk for symptoms of GERD by bloating the abdomen and causing pressure that forces acid up into the esophagus. Food allergies may be responsible for some cases of gastroesophageal reflux disease in children. Studies show that cigarette smoking relaxes the LES and that obesity and pregnancy can also cause GERD.

Anyone who eats a heavy meal, particularly if one subsequently lies on the back or bends over from the waist, is at risk of an attack of heartburn. Anyone who snacks at bedtime is at high risk of GERD.

Persistent GERD may be due to abnormal biologic or structural factors which, as well as malfunction of the LES muscles, include defects or injuries in the lining of the esophagus, peristalsis problems, over-acidic stomach contents, amongst others. Some people may be sensitive to digestive factors other than acid; such substances can cause GERD symptoms, but are likely to be missed during a medical examination.

Indigestion might be caused by a disease or an ulcer in the digestive tract, but for most people it is simply a result of eating too much, eating too quickly, eating high-fat foods, or eating during stressful situations. Smoking, drinking too much alcohol, using medications that irritate the stomach lining, being tired, or having ongoing stress can also cause indigestion or make it worse.

In one study, over half of GERD patients showed abnormal nerve or muscle function in the stomach, which caused impaired motility - an inability of the muscles to contract normally. This causes delays in stomach emptying, increasing the risk of acid reflux.

In a small percentage of chronic patients, a serious form of GERD called Barrett's esophagus may eventually develop, in which the erosion can lead to cancerous changes in the tissue lining of the esophagus. It should be noted that symptoms of GERD may be present without any signs of injury to the esophagus.

Using antacids and other acid blockers can begin a vicious cycle. When the acid is neutralized, the LE sphincter is weakened. This allows any remaining acid to sometimes slip past and irritate the esophagus. So, you take an antacid and you feel better, because you lessen even more what little acid remains that has been irritating your already sensitive esophagus. This really is not the solution to the problem.

Acid reflux during the night tends to be more harmful than during the day because it is associated more with complications such as narrowing the esophagus, alterations of the esophagus and cancerous changes of the esophagus and esophageal cancer.