A new finding may mean less stomach pain and heartburn for many who experience discomfort after drinking a cup of coffee.

Researchers studied the irritants in coffee by exposing cultures of human stomach cells to a variety of different coffee preparations, including regular, dark-roast, mild, decaffeinated, and stomach-friendly. They then identified several substances that appeared to trigger chemical changes associated with increased acid production. These substances include caffeine, catechols, and other ingredients.

"Our data show, for the first time, that caffeine, catechols and N-alkanoly-5-hydroxytryptamides are those coffee components that stimulate molecular mechanisms of stomach acid secretion in human stomach cells," said lead researcher Dr. Veronika Somoza.

They also unexpectedly found that one of the coffee components, N-methylpyridium (NMP), seems to block the ability of the stomach cells to produce hydrochloric acid and could provide a way to reduce or avoid stomach irritation. Since NMP is generated only upon roasting and not found in raw coffee beans, darker-roasted coffees contain higher amounts of this stomach-friendly coffee ingredient.

Estimates suggest that up to 40 million people in the U.S. either avoid coffee, or cannot drink as much as they like, due to stomach irritation.

In addition to avoiding foods that cause stomach irritation, medical experts say digestive health supplements containing hydrochloric acid may help fight acid reflux, heartburn and other digestive problems.