Reducing children’s exposure to a variety of allergens, rather than targeting a single “trigger,” might be a better way to avoid asthma, according to a new review of studies.

While some children are genetically predisposed to developing the disease, parents might still be able to prevent or delay the onset of symptoms by minimizing exposure to likely allergens.

“Breastfeeding and house dust mite reduction seemed to be the most important interventions,” used in the studies, said review author Tanja Maas. “The food interventions focused on hydrolyzed formula as opposed to regular formula. The use of hydrolyzed formula was not shown to have any preventive effect. Breastfeeding, however, seemed to be very effective.”

Reviewed studies focused on 3,271 high-risk children — those having at least one close relative with asthma.

The review appears in the current issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates research in all aspects of health care. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing trials on a topic.

Led by Maas, a researcher of immunological disease at Maastricht University Medical Center, in the Netherlands, the authors analyzed nine studies. They classified three of the studies as multifaceted, taking more than one approach to asthma prevention. These studies covered both inhalant and dietary types of allergen reduction, while the remaining six studies looked at one type of allergen reduction alone.

Dietary restrictions started in pregnancy or from the child’s birth. In studies that included a dietary approach, mothers were encouraged to breastfeed or use special formula and to delay the introduction of solid foods into the child’s diet. Environmental interventions included the reduction of dust mites, pet allergens and exposure to tobacco smoke in the child’s immediate environment.

The majority of allergic sensitization probably happens in early childhood or adolescence.

“We see most seasonal allergy sensitization occur by five years of age,” said pediatric allergist Harvey Leo, M.D., an assistant research scientist at the Center for Managing Chronic Disease at the University of Michigan. “Eighty percent of food allergies are present by two to three years of age.”

Complicating study results was the fact that physicians cannot make a definitive diagnosis of asthma in children younger than five years, although the studies did include children whose parents had reported asthma-like symptoms such as wheezing and nighttime coughing.

“Children under the age of five are too young to diagnose with asthma, as the instructions used in determining lung-function measurements are too difficult for a child to comprehend, but asthma-like symptoms give some information on the respiratory health of the child,” Maas said.

Allergen exposure is only one piece of the puzzle; family history is another.

“Allergies and asthma seem to be influenced by gene-environment interaction,” Maas said. “This means that persons with a genetic susceptibility develop these diseases more often if they are exposed to specific environmental influences. The environmental causes, however, are not totally clear. What we do know is that avoiding multiple allergen exposures seems to be helpful in the prevention of the disease.”

“Studies suggest that if no parents had a history of asthma, there is a 6 percent chance of developing asthma,” Leo said. “If one parent has a history of asthma, there is a 20 percent chance the child may develop asthma. If both parents have a history of asthma, the child has a 40 to 60 percent chance.”

While the review can serve as a starting point for further research, the results do not conclusively point to any definitive advice that parents can follow.

“Due to the lack of consistent data, it would be hard to have families make environmental or dietary changes alone to prevent further development of asthma or other allergic diseases, even if their children are from a high-risk group,” Leo said. “It is unlikely that there is a single thing a parent can do, such as dust mite precautions or avoiding cow’s milk formula in infancy to reduce the chance of development of asthma.”

What parents can do: “Early attention to nighttime cough or wheezing in high-risk children may warrant early discussion with the child’s physician or a specialist for possible intervention, either medical or avoidance based,” Leo said.

The Cochrane Collaboration is an international nonprofit, independent organization that produces and disseminates systematic reviews of health care interventions and promotes the search for evidence in the form of clinical trials and other studies of interventions. Visit http://www.cochrane.org for more information.

Maas T, et al. Mono and multifaceted inhalant and/or food allergen reduction interventions for preventing asthma in children at high risk of developing asthma (Review). Cochrane Database of Systematic Reviews 2009, Issue 3.

Source: Health Behavior News Service