Asthma and allergies continue to be major public health problems in affluent westernized countries. Changes in dietary habits dating from before the increase in asthma prevalence may have a role in the development of asthma and allergies. Many studies have investigated the role of specific nutrients in asthma and allergies, and intervention studies with supplementation of particular nutrients have been conducted, but results have been mixed. It is likely that nutrients may exert their strongest effect early in life, when both the immune system and the lungs are not yet fully developed.