Diet May Help Combat Allergies and Asthma

27/11/06 A recent publication from the Global Allergy and Asthma European Network (GA2LEN) provides new insights into the role that diet may play in the development of allergies, especially in children. The work suggests that the significant changes in European diets over the past 20-40 years may have contributed to the increased incidence of allergic diseases in both children and adults seen over this period. Members of the nutrition work package responsible for the report consider that its findings are just the beginning of GA2LEN's potential role in greater understanding of this complex area.

The prevalence of allergic diseases has increased dramatically over the past few decades, especially in children. One child in three is allergic today and one in two people in Europe are likely to be suffering from at least one allergy by 2015. It is generally agreed that a combination of heredity and environmental factors is responsible for the development of the allergy and asthma. However, the evolution of these diseases has been far too rapid for genetics to be the sole explanation. Among the wide range of environmental factors under discussion, changes in the European diet in the last 20-40 years are considered to be a possible explanation. Indeed, the way in which children are fed early in life may have a direct effect on the subsequent development of asthma and allergies, according to a recent publication from the Global Allergy and Asthma European Network (GA2LEN).

In a paper entitled "Nutrition and allergic disease", published this year in Clinical and Experimental Allergy Reviews, 12 European experts working together in the GA2LEN nutrition work package present the evidence and define fertile topics for future research. The work package team is led by Professor Philip C Calder, Institute of Human Nutrition, University of Southampton.

Key findings: breastfeeding, early diet and probiotics

The three main areas producing key findings are breastfeeding, intake of certain nutrients, and probiotics.

Exclusive breastfeeding, that is providing the infant with no other liquid or food other than breast milk, is believed to be effective in reducing subsequent development of allergies. It appears that exclusive breastfeeding for four months helps protect the child from cow's milk protein allergy until 18 months, reduces the likelihood of dermatitis (skin allergy) until three years, and reduces the risk of recurrent wheeze (or asthma) until six years' of age. However, the longer term effects of breast feeding on allergic outcomes are not known and require investigation.

The protective effect of four months of exclusive breastfeeding is important for all children but it is especially valuable for those at high risk of developing allergies. Children are at high risk of developing allergies if one or both parents are affected by allergic disease. If it is not possible for the high-risk child to be breastfed, hypoallergenic formula combined with avoidance of solid foods for 4-6 months offers an alternative source of protection. The studies show that hypoallergenic formula helps prevent cows' milk protein allergy developing before the age of five years and offers protection against atopic dermatitis (eczema or other skin allergy) until the age of four years.

A second major area of importance appears to be the components of the diet. For example, antioxidants in the diet, such as vitamin C, vitamin E and selenium coming mainly from fruit and vegetables, may have a protective effect. Furthermore, different fats found in milk, butter, vegetable oils and fish may have different effects on development of allergies and asthma. Although it is difficult to find clear-cut evidence, it appears that reducing sodium intake, increasing magnesium intake, eating apples and other fruit and vegetables, and avoiding margarine might help some asthmatics. However much of the research conducted to date has not been systematic in its approach and this makes the drawing of hard conclusions very difficult.

The role of probiotics and prebiotics in the diet is promising. Living organisms such as probiotics appear to protect against the development of allergies by producing changes in the bacteria in the gut that stimulate the immune system. A double blind, placebo-controlled study has recently shown that probiotics can help reduce the risk of atopic disease. This is an important area for future research.

Meeting the challenge

The review highlighted several areas in nutrition and diet that appear to be fruitful for future research in allergic disease, and therefore for future disease control. In particular, it has highlighted gaps in relation to specific effects of maternal and infant nutrition on allergy and asthma in later life. Patients, health professionals and policy makers alike would benefit from such research and from more large-scale studies on diet and allergy. Key focuses should be identification of dietary patterns or factors likely to be involved in altering risk of development of allergies and asthma, and developing the evidence base about whether supplementation with specific fats or probiotics could contribute both to the protection and treatment of allergic diseases. The studies required will need to be large and to be well planned, designed and executed. They are likely to require cross-country collaboration.