Heartburn in bed: soda, sleeping pills can spoil sleep.

For many people, meals come with an unwanted side order: heartburn. But heartburn has a more sinister aspect that can show up well after people leave the table. Acid reflux at night, which can have serious long-term health consequences, often causes sleep problems, suggests a new medical survey.

The pain of heartburn results from acidic stomach fluids rising into the esophagus. Various factors, including what a person eats and drinks, can weaken the gate-like sphincter muscle that normally confines the fluids to the stomach.

Estimates of the prevalence of all forms of reflux range from about 10 percent to nearly 50 percent of adults. According to the new report, about one-quarter of adults are aroused from sleep by heartburn at least twice a month. "It is a stunning number," says gastroenterologist Ronnie Fass of the Southern Arizona VA Health Care System in Tucson, who led the study.

Being awakened by reflux is bad enough, but sleeping through the irritation can be worse, Fass says. When asleep, people produce little acid-neutralizing saliva and may not swallow, an action that ushers straying gastric fluids back to their place. Lingering acid can lead to problems such as chronic esophageal inflammation, coughing, or asthma, Fass says.

Compared with daytime heartburn, "nighttime reflux is a much more malignant form of the disease," says William C. Orr of the Oklahoma University Health Sciences Center in Oklahoma City.

To understand factors linked to nighttime heartburn, Fass and his colleagues distributed a questionnaire to volunteers in several long-term health studies. Some 15,000 people completed the questionnaire. Subsets of people with and without nighttime heartburn also answered questions about health problems, medication use, and beverage intake.

A variety of factors were more prevalent among people with nocturnal reflux than among those without it. They included excessive weight, high blood pressure, asthma, insomnia, and obstructive sleep apnea. Some of these factors had previously been associated with reflux in general.

Fass notes that insomnia and sleep apnea could be consequences, rather than causes, of nighttime reflux.

Many patients with disturbed sleep "don't make the connection" to reflux and seek treatment only for sleeping problems, Fass says.

"Carbonated beverages are highly associated with reports of heartburn during sleep," says Fass. Also implicated are benzodiazepines such as Valium and Xanax, medications often used to treat sleep problems, Fass and his colleagues report in the May Chest. Past studies have shown such drugs to increase the frequency of reflux in general.

If suffering from nighttime reflux, "I would definitely avoid carbonated beverages in the evening [and] not have benzodiazepines as sleeping pills," Fass says.

Health care providers need to be aware of the problems associated with nighttime reflux, says Harley Liker of the University of California, Los Angeles. According to research that he and his colleagues presented this week in Chicago at the annual medical conference called Digestive Disease Week, about half of people with recurrent reflux report being awakened by heartburn, which typically costs them 3 to 4 hours of sleep per week.

Heartburn is often treated with acid-blocking medications. However, a person with reflux who visits a physician because of sleep loss "may not complain directly of heartburn," Orr says. "That patient could probably be cured of both problems simply by curing their reflux."