SALZBURG, AUSTRIA—Studies have shown that children who grow up on farms have a reduced risk of allergic disease. Although the reason for this is unclear, the farm environment has been linked with microbial exposure that activates an efficient T helper 1 immune response.

Recently, European investigators took this finding a step further when they assessed whether the timing of exposure to a farm environment affects the degree of protection from allergic disease.[1] They discovered that children exposed to a farm environment in the first year of life had significantly lower rates of asthma, atopy, and hay fever than did those exposed later in life.

SURVEY OF RURAL AREAS

Riedler et al performed a cross-sectional survey of rural areas in Austria, Germany, and Switzerland, where most farms are family run and include cattle, pigs, sheep, poultry, horses, and/or goats. The respondents, parents of children ages 6 to 13 years, completed a questionnaire about asthma and allergy in their offspring.

In addition, parents were interviewed about the timing, frequency, and amount of their children’s exposure to stables, farm animals, and pets. The interviewers also asked about the mothers’ farming activities, duration of breast-feeding, timing of farm food and milk consumption, vaccinations, and avoidance of allergens. The children underwent serum immunoglobulin E tests.

ASTHMA, HAY FEVER, AND ATOPY RATES

The final analysis included 319 children from farming families and a random sample of 493 children from non-farming families in the same rural areas. When these two groups were compared, the investigators found that, as they had hypothesized, the prevalence of asthma and allergy was markedly lower in the children from farming families.

Further analysis showed that early exposure to a farm environment had a consistently protective effect. For example, the prevalence of asthma was 1% in children exposed in the first year of life and 11% in those exposed between ages 1 and 5 years. Hay fever prevalence was 3% and 13%, respectively; atopy prevalence was 12% and 29%, respectively. Continuous exposure to a farm environment in the first five years of life was the most protective of all: In the children with continuous exposure to environments of this sort, the rates of asthma, hay fever, and atopy were 0.8%, 0.8%, and 8.2%, respectively.

Allergic disease protection was specifically associated with exposure to stables and with drinking raw, unpasteurized farm milk. Furthermore, these two protective factors appeared to have additive effects. Regular contact with farm animals has been shown to have protective effects. Farm milk may prevent asthma and allergy because it contains more lipopolysaccharide and other noninfectious microbial components than does pasteurized milk, the investigators suggested.

ASTHMA RISK AND ATOPY UNRELATED

Interestingly, Dr. Riedler and colleagues also found that the reduction in asthma risk conferred by exposure to a farm environment was unrelated to the child’s level of atopic sensitization. The authors concluded that their findings could help to improve our understanding of the origins of asthma and allergy and lead to the development of prevention strategies.

—Timothy Begany