Heartburn is the new normal.

Acid reflux is on the rise in the United States, with 25 million people experiencing daily symptoms, according to the American Gastroenterology Association, up from 15 million 10 years ago.

Another 60 million people say they have heartburn once a month.

That's a whole lot of tummy trouble. Blame stress and an aging population -- and above all, experts say, blame Americans' habit of eating too much.

Turn 40, and suddenly conversations about digestive issues take on urgent fascination. Garlic just doesn't sit right anymore. Or Mexican food, maybe -- or onions, or red wine. Or all of the above.

The ubiquity of acid reflux has turned it into a touchstone of middle-aged American culture, with over-the-counter medications proliferating in TV commercials and a loony variety of remedies such as magnetic bracelets offered over the Internet.

Friends compare symptoms and remedies on Facebook. Sleeping through the night undisturbed by heartburn and digestive backup becomes a major life goal. The nightstand with the reading glasses and small vial of Tums has become a mainstay of 50-year-olds' home decor.

Relax, midlife Americans. It's not age. It's chronic overindulgence.

"There was one guy who came in; it turned out that it was Girl Scout cookie season," said Dr. Ronald Hsu, a gastroenterologist at Sutter Roseville Medical Center in Roseville, Calif. "Instantly, we had a diagnosis."

Extra weight around the middle, it turns out, is one of the major culprits behind chronic gastroesophageal reflux disease. More than 40 percent of the population reaches for antacids more than once or twice a week, suffering from heartburn that's serious enough to check out with a doctor.

Here's how acid reflux works. When the sphincter muscle at the top of the stomach is weak, acid can backwash into the esophagus during digestion, leading to a range of reflux-related symptoms -- everything from heartburn and queasiness to coughing, asthma and a predisposition for hiccups.

The problem can be especially troublesome at night, with episodes of heartburn interrupting sleep. The solution? Don't go to bed with a full stomach; a light dinner eaten three hours before bedtime is a good idea. Also, avoid sleeping on your back.

"Anything that increases stomach pressure increases reflux," Hsu said. "People who are more obese have more symptoms. Pregnant women can have more reflux."

Even modest weight gain can lead to problems with acid reflux. Women with a body mass index of 25 to 27, considered only slightly overweight, are more than twice as likely to develop the disease, Boston University researchers have found.

So what to do? First, avoid mint-flavored antacids. Mint relaxes the valve between the stomach and the esophagus, making the problem worse.

For many people, losing weight helps ease the stomach pressure and resolve their reflux. Others find that avoiding a list of comestibles that make life worth living -- chocolate, spicy foods, citrus fruits, alcohol and caffeine -- can help alleviate acid reflux symptoms.

Over-the-counter medications can help, too. Proton pump inhibitors, such as Prilosec and Prevacid, can block the release of acid in the stomach and, when taken regularly, provide long-term relief.

Unfortunately, for a small percentage of sufferers, chronic acid reflux is more than a discomfort and an inconvenience -- it's a factor in making esophageal cancer the fastest growing cancer in the country.

Repeated exposure to stomach acid over many years' time can cause cellular level changes to the esophagus leading to a disorder called Barrett's esophagus -- which, left untreated, can contribute to the development of esophageal cancer.

The incidence is still small, with only about 16,600 new cases a year, but experts consider it a particularly difficult cancer. More alarming, the incidence of esophageal cancer is rising quickly, while other cancer rates are decreasing, Hsu said.

Particularly at risk are middle-aged and elderly men with a long history of acid reflux and, much of the time, problems with obesity.