A common belly bug once thought to be harmful may have beneficial effects early in life. Researchers at the New York University (N.Y.U.) Langone Medical Center have found that a lack of Helicobacter pylori—a microbe that thrives in the human stomach—may be linked to childhood asthma and other allergies.

They report in The Journal of Infectious Diseases that children ages three to 13 years were 59 percent less likely to have asthma and 69 percent less likely to have hay fever and other childhood allergies if they tested positive for the bacterium. The question is whether the benefits outweigh the potential risks later in life. H. pylori has been linked to the development of peptic ulcers and gastric cancer in adults after their third decade.

The finding suggests that doctors may even consider introducing the bacteria to kids whose natural supplies have been destroyed, says study co-author Martin Blaser, an N.Y.U. infectious disease specialist.

"In the future, physicians may give children a mix of H. pylori strains to optimize their health early in life, and then use antibiotics to eradicate the organism in a patient's 40s," Blaser says.

H. pylori is acquired during childhood, usually from close contact with parents and siblings. Beginning in the early 20th century, clean water, smaller families, better nutrition and the widespread use of antibiotics in industrialized nations led to a dramatic decline in this microbe. Only about 5 percent of children in this study who were under 10 years of age were found to harbor H. pylori compared with developing nations, where most children test positive.

During the second half of the 20th century, there was a spike in asthma rates, particularly in countries where the bacteria were disappearing; in the U.S., for instance, asthma rates for children below the age of 17 jumped from 3.6 percent in 1980 to 8.9 percent in 2005.

Blaser says the microbe has been residing in the human stomach for at least 50,000 years. When present, it dominates the microbial ecosystem of the gut and interacts with the stomach lining's cells. The immune system cannot eliminate the organism, but "it has learned to live with it by regulating the inflammatory responses induced by H. pylori," he notes.

The study echoes previous findings that suggest that H. pylori can benefit people harboring it, according to William Tremaine, a professor of medicine at the Mayo Clinic in Rochester, Minn, who was not involved in the study. For example, children with inflammatory bowel disease tend to test positive for the microbe less often than other children. All of that may mean that in the recent past, "H. pylori may have offered a survival advantage by blocking the onset of debilitating and potentially fatal diseases that start earlier in life than gastric cancer," Tremaine wrote in an e-mail.

Future studies will examine if H. pylori interactions in the stomach play a direct role in tempering broader immune responses to environmental allergens. As Hidekazu Suzuki, an associate professor at the Keio University School of Medicine in Tokyo, who was not involved in the study, notes in an e-mail, this work suggests a "new trend for the basic and clinical research of H. pylori-associated diseases."