Preventive measures and their effects. Results from cohort studies.

The prevalence of asthma and atopic diseases continues to rise. Genetic factors alone cannot explain this rapid rise and the immunological mechanisms involved are insufficiently explained to allow direct intervention on a population-wide scale. Long-term observational birth cohort studies have provided data on which primary prevention studies are based. This review discusses the "who", "how", "when" and "what" of primary prevention and the experiences to date in prospective intervention cohort studies. Copyright 2002 Elsevier Science Ltd.