Allergies making your life miserable? Tired of popping antihistamines like candy? Can't go anywhere without your inhaler? The real problem may not be your stuffed-up head. It could be the microbes in your gut.

At a recent meeting of the American Society for Microbiology, scientists from the University of Michigan Medical School presented results of experiments with laboratory mice indicating that antibiotic-induced changes in microbes in the gastrointestinal tract can affect how the immune system responds to common allergens in the lungs.

"We all have a unique microbial fingerprint – a specific mix of bacteria and fungi living in our stomach and intestines," says Gary B. Huffnagle, Ph.D., an associate professor of internal medicine and of microbiology and immunology in the U-M Medical School . "Antibiotics knock out bacteria in the gut, allowing fungi to take over temporarily until the bacteria grow back after the antibiotics are stopped. Our research indicates that altering intestinal microflora this way can lead to changes in the entire immune system, which may produce symptoms elsewhere in the body."

If confirmed in human clinical studies, Huffnagle believes his research findings could help explain why cases of chronic inflammatory diseases, like asthma and allergies, have been increasing rapidly over the last 40 years – a time period that corresponds with widespread use of antibiotics.

To test Huffnagle's hypothesis, Mairi C. Noverr, Ph.D., a U-M research fellow in internal medicine, gave a five-day course of oral antibiotics to normal lab mice followed by a single oral introduction of the yeast, Candida albicans, to create a consistent, reproducible colony of microbes in the stomach and intestines. Candida albicans is normally found in the GI tract, and increased growth of Candida albicans in the gut is a common side-effect of antibiotics.

Two days after stopping the antibiotics, Noverr exposed the mice to a common mold allergen called Aspergillus fumigatus by placing spores in the nasal cavities of all the mice in her study. She then examined the mice for the presence of an allergic response in the airways.

"After antibiotics changed the mix of microbes in the GI tract, the mice developed an allergic response in the lungs when exposed to common mold spores," Huffnagle explains. "Mice that didn't receive the antibiotics were able to fight off the mold spores."

Huffnagle thinks that disruptions in the growth of bacteria and fungi in the GI tract somehow interfere with the immune response to respiratory allergens.

"We know from laboratory experiments that dietary antioxidants called polyphenols, which are found in fruits and vegetables, can limit fungal growth and that a diet high in saturated fats and sugars slows the recovery of normal gut microflora," Huffnagle adds. "The Mediterranean diet is rich in sources of polyphenols, so it's intriguing that Mediterranean-diet countries have lower rates of allergies, asthma and other inflammatory diseases than Western-diet countries like the United States, Canada and England .

"If we can determine exactly how microflora in the GI tract affect the immune system, it may be possible one day to prevent or treat allergies and inflammatory diseases with diet changes or probiotics – dietary supplements of ‘healthy' bacteria designed to restore the normal balance of microbes in the gut," Huffnagle adds. "In the medical community, probiotic therapy is becoming an area of increasing interest."

Until then, Huffnagle emphasizes the importance of a healthy low-sugar diet, with lots of raw fruits and vegetables, after being treated with antibiotics to help restore the normal mix of microbes in your GI tract as quickly as possible. "The old saying, ‘an apple a day keeps the doctor away' may be more true than we thought," he says.

For more information:

U-M Health Topics A-Z: What is an Allergy?
http://www.med.umich.edu/1libr/aha/umalerg03.htm

U-M Health Topics A-Z: Facts about Asthma
http://www.med.umich.edu/1libr/aha/umastfacts.htm