Identifying high-risk infants

Identification of babies who are genetically predisposed to asthma before or shortly after birth means that parents can be given timely advice on dietary factors that may be involved in the development of asthma.

Of these, the presence of a family history is most useful in identifying at-risk neonates in routine clinical practice. Other indices (eg cord blood IgE, development of positive skin tests to food allergens during infancy, IgE responses to respiratory tract infections) have proven useful in research settings but may be difficult to perform in routine clinical practice.

Primary preventive measures target a population that is still healthy but at risk of a disease, mostly using a range of interventions. However, it remains uncertain whether manipulation of factors associated with the development of asthma can reduce prevalence or delay onset.

Pregnancy

Contrary to popular belief, there is no evidence that the elimination of major allergens from the maternal diet during pregnancy is effective in preventing allergic disease in the genetically predisposed infant.⁹ The Cochrane review into the subject⁹ found that restricted diet during pregnancy was associated with a slightly but statistically significantly lower mean gestational weight gain, a non-significantly higher risk of preterm birth, and a non-significant reduction in mean birthweight.

Pregnant women should be encouraged to eat a wide variety of foods and not to eliminate potential allergens unless they are allergic to them themselves.^{9 Level I Evidence}

Breastfeeding

It is well recognised that breastfeeding confers health benefits to both mother and infant. Breast milk provides specific and non-specific factors that have long-term consequences for early metabolism and the development of disease through:³⁷

• enhancing the immature immunological system of the neonate
• strengthening host defence mechanisms against infective and other foreign agents
• promoting gastrointestinal mucosal maturation
• altering gut microflora
• immunomodulatory and anti-inflammatory functions
• hormones, growth factors and cytokines, which may modulate the development of disease.

It is generally recommended that, where possible, infants be exclusively breastfed for the first 6 months of life.^38-39 Level I Evidence

Breastfeeding and asthma

Many recent studies have investigated whether breastfeeding has a protective effect on the development of atopic disease and/or asthma with the following findings.

Some longitudinal studies have disagreed with the studies outlined above, finding an increased risk of asthma in later life among children who had been breastfed.^41-42 However, there are methodological concerns with these studies (eg duration and exclusivity of breastfeeding and small sample size).⁴³

Breastfeeding and maternal asthma

Some studies have investigated whether breastfeeding in the presence of maternal asthma increases the risk of the child developing wheeze or asthma. While one study found an association with an increased risk of asthma and recurrent wheeze for atopic children with mothers with asthma,⁴² a more recent study found a protective effect from breastfeeding regardless of maternal asthma status.¹⁶ In that study, breastfeeding was associated with lower rates of asthma in children whose mothers had asthma and in atopic and non-atopic children.

Exclusive breastfeeding for at least 4 months may reduce the likelihood of asthma developing or delay its onset.^{14, 17 Level II Evidence}