A common stomach bug may prevent asthma.
A lung-stomach connection. I'm Bob Hirshon and this is Science Update.
People with a common stomach infection called Helicobacter pylori are 40 percent less likely to get childhood asthma and allergies. This according to microbiologist Martin Blaser, chair of the New York University Department of Medicine. Blaser says that chronic Helicobacter infections were almost universal before the age of antibiotics.
So, as a result, we now have people—I think for the first time in human history—adults, who either have the organism or don't, and so we can measure the consequences.
The bug has already been shown to have both costs and benefits to the gastrointestinal tract. As for the asthma connection, Blaser suspects the infection keeps the immune system occupied, reducing the likelihood that it will trigger an asthma attack. I'm Bob Hirshon, for AAAS, the science society.
Making Sense of the Research
Asthma and allergies, especially in children, have steadily increased over the last several decades, and the increase can't be explained just by better reporting and more accurate diagnoses. Severe peanut allergies, for example, were very rare a few decades ago, but are now so much more common that many schools have banned peanuts completely from the premises.
However, this isn't the case in the developing world. In fact, allergies and asthma are very rare in developing countries, and continue to be. This has led many scientists to speculate on why children in industrialized countries have become so susceptible. One popular theory in recent years has been that children in modernized countries grow up in sterilized environments, relatively free of the normal environmental particles, microbes, and parasites that people living in more earthy settings are exposed to daily. As a result, the theory suggests, their immune systems aren't kept as busy as they should be, and so they mistakenly attack harmless particles, like peanuts, when given the opportunity. But this theory has some holes in it: for example, is a child in New York City really living in a more "sterile" environment than a child in the mountains of Tibet?
Now, Blaser's work suggests that asthma and allergies may, in part, be related to the absence of this stomach infection—which in turn, may be caused by antibiotics. Children today are given antibiotics for all sorts of ailments, like earaches. Every time a child takes an antibiotic, it kills not only the bacteria that are causing the infection, but other bacteria that live in the body—whether they're good or bad for you. Given enough antibiotics, some of these infections may be killed off completely, never to return.
In this case, getting rid of Helicobacter has both pros and cons. A long-term Helicobacter infection causes stomach inflammation, called gastritis, and increases your risk of getting ulcers and stomach cancer later in life. On the other hand, the infection actually reduces your risk of getting some kinds of esophageal cancer. That's because the bacteria lowers your stomach acid, making it less likely to splash into the esophagus (a condition known as acid reflux) and damage its lining.
But why the connection to allergies and asthma? Well, Blaser suspects that it's chronic, internal infections like Helicobacter—rather than environmental microbes—that have kept our immune systems busy in the past. He points out that we encounter most microbes in the environment only in passing, whereas a chronic infection is something we live with every day. That could explain why developing countries have so few allergies. And it just so happens that in parts of Asia and Africa today, 80 to 90 percent of the population is infected with Helicobacter infection.
It's important to note that while Blaser's data come from a scientific study, his explanation for the data is his own theory, based on circumstantial evidence. Nothing in the data proves that Helicobacter actually protects against allergies; it's possible that people with allergies just tend to be less susceptible to the bacteria for some other, unrelated reason. Still, it's intriguing to consider that anything in modern medicine, even accidentally eradicating a cancer-causing stomach infection, may have unintended side effects.
Now try and answer these questions:
- What is Helicobacter pylori? How has its relationship to the human population changed?
- What are the positives and negatives associated with a Helicobacter infection?
- Do you agree with Blaser's theory? Why or why not?
- Suppose a common, chronic skin infection was also shown to be protective against asthma and allergies. Would this support, or weaken, Blaser's theory? Explain why.
You may want to check out the May 18, 2007, Science Update Podcast to hear further information about this Science Update and the other programs for that week. This podcast's topics include: how grilling could take a toll on your health, why smarter doesn't equal richer, an infection that could help prevent asthma, a step toward fusion reactors, and the closest living descendants of dinosaurs.
In the National Geographic News article, Deciphering the “Bugs” in Human Intestines, read about the microbial communities in the human intestine. Much of what lives within the human gut is unexplored.
All About Allergy, part of the National Pollen Network's Allernet site, contains information about types of allergies and their causes.