The "hygiene hypothesis" is a theory that young children who are exposed to a variety of germs will have a lower risk of developing asthma and allergies later in life. Studies on the hypothesis have been inconsistent. The latest study, published today in the American Journal of Respiratory and Critical Care Medicine, concludes that daycare has no effect on later respiratory illnesses.
The researchers, in the Netherlands, followed nearly 4,000 Dutch children over eight years. Parents completed questionnaires at various intervals of the child's life, from pregnancy to age 8. At that age, more than 3,500 of the children were assessed for specific allergies and asthma. Daycare use was also assessed each year.
The study found that children who started daycare early were twice as likely to experience wheezing in the first year of life compared with those who didn't go to daycare. But as the children became older, the illness pattern shifted. There was a trend for less wheezing among early attendees. By age 8 there was no association between daycare attendance and wheezing. The only children who stood out in the study were those who had early daycare attendance and older siblings. Those children had more than a fourfold higher risk of frequent respiratory infections and more than twofold risk of wheezing in the first year compared with children without older siblings and daycare.
"Children exposed to both early daycare and older siblings experienced most infections and symptoms in early childhood, without a protective effect on wheeze, inhaled steroid prescription or asthma symptoms until the age of eight years," the lead author of the study, Dr. Johan C. de Jongste, said in a news release. "Early daycare merely seems to shift the burden of respiratory morbidity to an earlier age where it is more troublesome than at a later age. Early daycare should not be promoted for reasons of preventing asthma and allergy."
-- Shari Roan
Photo credit: Luis Sinco / Los Angeles Times