Feb. 11, 2000 (Los Angeles) -- Zealous hygiene and a "semisterile" diet could be contributing to the epidemic of asthma and respiratory allergies currently afflicting industrialized nations, according to researchers in Italy. The results of the study support the "hygiene hypothesis," which proposes that modern practices of sanitation and, possibly, vaccination could be depriving people of the defenses needed to prevent asthma and allergies.
Allergies affect 40-50 million people in the U.S. and are the sixth leading cause of chronic disease, according to the American Academy of Allergy Asthma & Immunology. More than 17 million Americans currently are estimated to have asthma, which claims more than 5,300 lives each year. Between 1980 and 1994, the prevalence of asthma increased by 75%.
The results of the Italian study support a theory known as the hygiene hypothesis, which states that modern methods of hygiene and sanitation have decreased children's exposure to certain microbes in food and water, preventing them from building defenses to those organisms and increasing their risk of developing allergies. In a separate study of more than 11,000 young Italian men, lead author Paolo M. Matricardi, MD, and his colleagues found a direct correlation between a condition called atopy -- a tendency to develop an allergic reaction -- and socioeconomic status. Matricardi tells WebMD that "this positive association is confirmed in other European countries, like the U.K., and is one of the indirect pieces of evidence supporting the so-called hygiene hypothesis."
In this study, which appears in the current issue of the British Medical Journal, Matricardi, research director of the Laboratory of Immunology and Allergy at the Institute of Experimental Medicine in Rome, and his colleagues looked at male Italian Air Force cadets aged 17-24. They found that individuals with more allergies had fewer antibodies to a number of organisms, bacteria, viruses, and parasites transmitted through food, saliva, or feces, indicating that they had not been exposed to these organisms. Conversely, asthma was rare and allergies infrequent among the men who had evidence of antibodies against at least two of the organisms tested for in their blood.
"These findings are not surprising. There is a growing body of evidence that things that happen to an infant early in life -- perhaps even in the uterus -- may influence whether or not that baby becomes allergic," says Paul Williams, MD, clinical professor of pediatrics and environmental health at the University of Washington in Seattle. He tells WebMD there is evidence that other environmental factors, such as early exposure to antibiotics, living in the city or on a farm, family size, and even birth order may influence a child's tendency to develop allergies or asthma.
However, Williams, who was not involved in the study, warns that the hygiene hypothesis is far from proven. "There is suggestive evidence that intestinal bacteria [that can be transmitted by mouth] influence the development of allergies, but no firm conclusions can be drawn yet." To minimize the chances of a child developing allergies, he encourages women to breastfeed, as this promotes the establishment of normal bacteria in the baby's intestinal tract, and recommends more judicious administration of antibiotics to babies.
- In the U.S., 40-50 million people suffer from allergies, and more than 17 million have asthma, a disease that claims more than 5,000 lives each year.
- One hypothesis suggests that modern hygiene, vaccines, and sanitation decrease children's exposure to certain microbes, preventing their immune systems from building up natural defenses.
- A new study adds further evidence to this hypothesis, showing that people who do not have antibodies to bacteria, viruses, and parasites transmitted via food, saliva, or feces are more likely to have allergies or asthma.