Bacteria that cause ulcers may have upside

For two decades, doctors have considered it their mission to kill every H. pylori bacterium they could find. But several recent studies have suggested that H. pylori, a major cause of ulcers and stomach cancer, may also reduce the risk of obesity and protect against a deadly form of esophageal cancer.

''H. pylori has been a part of us for as long as we have been humans," said Dr. Martin Blaser, chairman of the Department of Medicine at New York University, president-elect of the Infectious Diseases Society of America, and a specialist in H. pylori. ''It is not surprising that this organism may be beneficial in some ways to human health."

New research is showing that the organism may affect hormones made by the stomach that regulate appetite. A February article in the World Journal of Gastroenterology suggested that H. pylori increases production of a hormone called leptin that makes people feel full. And a 2003 article in the journal Gut suggested that H. pylori decreases production of a hormone called ghrelin that makes people feel hungry.

A January study in the journal Digestive and Liver Disease found that patients treated for H. pylori actually gained weight and their cholesterol levels rose after treatment.

''Everybody thinks the rise in obesity we are seeing in the western world is because we're eating too many Big-Macs," Blaser said. ''Another possibility is that it is due, in part, to a change in our micro-ecology. For the first time ever, we are having a generation of children growing up without H. pylori."

In the early 1900s, nearly all humans were colonized with H. pylori. But over the past century, hygiene has improved considerably, particularly in the developed world, and this has greatly limited the spread of the organism. Furthermore, antibiotic use has taken its toll on H. pylori. Since H. pylori was first identified in 1982, doctors have made a point of giving patients with the bacteria antibiotics to get rid of them.

''It used to be that more than 70 percent of children under the age of 10 carried H. pylori, and almost everyone did by adulthood," Blaser said. ''Now, just half of older adults in the developed world, and less than 10 percent of children, carry H. pylori, and the numbers continue to decline."

H. pylori's steady decline in the developed world has led to a dramatic reduction in gastric cancer. At the turn of the century, gastric cancer was the leading cause of cancer death in the United States; now, it ranks sixth. Rates of gastrointestinal ulcers have also dropped steadily over the past several decades as well.

''H. pylori causes an inflammatory response in the stomach," said Dr. Charles Bliss Jr., a gastroenterologist at Boston Medical Center who has done research on the bacterium. ''This damages stomach cells, which can cause ulcers, and may eventually lead to gastric cancer down the line."

But as the number of people with H. pylori has dropped, the incidence of a very aggressive type of esophageal cancer, called esophageal adenocarcinoma, has risen six-fold. The reasons for this rise are not entirely understood, however a connection to the decline in H. pylori has recently been suggested.

''There's definitely an association between the decline in H. pylori and the rise of adenocarcinoma of the esophagus," Bliss said. ''But it's really hard to say for sure that H. pylori actually protects against the cancer."

There are, however, reasons to believe that H. pylori protects against heartburn, a common affliction that can lead to esophageal cancer. In patients with such reflux, acid leaks into the esophagus, causing discomfort and damaging the cells of the esophagus, which increases the risk of cancer.

''After you treat an H. pylori infection in someone who has reflux symptoms, the reflux symptoms usually get worse," Bliss said.

H. pylori has an enzyme that neutralizes acid in the stomach. It also damages the cells in the stomach that produce acid, in effect reducing acid production. Both of these actions may limit acid leakage into the esophagus.

The jury is still out on whether the risks of H. pylori infection outweigh the benefits. Another recent study suggested that patients infected with H. pylori are at increased risk for a dangerous heart arrhythmia -- adding to the litany of possible negative effects of the organism.

For now, most doctors still prefer dead Helicobacter to living ones. But it is becoming clear that this organism is not entirely bad.

''Maybe we need to think twice about killing every H. pylori that we find," Bliss said. ''The decision may need to be made on a case-by-case basis that takes into account a particular patient's risk factors."