The pathophysiology of asthma in children involves many mechanisms. The role of breastfeeding is hypothesized to prevent asthma in children. Many studies have tried to find the relationship between breastfeeding and protective factors for asthma, but the results are still inconclusive.

Asthma is one of the chronic diseases that occur early in children. Around 14% of school-age children experience asthma. Asthma is hypothesized to be related to nutritional and environmental factors that influence the immune system in the early stages of life, and these effects cause permanent changes. The persistent immune system change is associated with various diseases, including asthma.

Breastfeeding Prevents the Occurrence of Asthma in Children

The Mechanisms of the Breastfeeding Effects on the Asthma Occurrence

The mechanism of the breastfeeding effects on the occurrence of asthma can be explained through 4 mechanisms, namely:
  1. epigenetic, 
  2. microbiota influence, 
  3. immunity and inflammation, 
  4. growth and improvement of lung function.

1. Epigenetic
The first mechanism is related to epigenetics. The epigenetic change in gene expression is hypothesized to be related to the development of the immune system. The epigenetic change that occurs at an early age will cause changes throughout life. Many epigenetics are associated with allergic and asthma events.

In some studies, breastfeeding can cause epigenetic changes in infants. Breastfeeding induces DNA methylation. Breastfeeding is related to the methylation of the leptin promoter gene associated with appetite. Breast milk also contains non-coding RNA that regulates gene expression, so that it is hypothesized that the effect of breastfeeding is not just DNA methylation. However, further research is still needed to understand the impact of epigenetics on breastfeeding and its relationship with asthma incidence.

2. Effects of Microbiota
The second mechanism is the influence of microbiota. Breastfeeding affects the development of oral microbiota and gastrointestinal tract in infants. Gastrointestinal microbiota is associated with the occurrence of asthma through the immune system. Breast milk contains antimicrobials that limit the baby's digestive tract's microbes, but Breast milk also contains oligosaccharides, which are the substrate for the growth of certain bacteria. Gastrointestinal microbes play an essential role in the formation of the baby's immune system. The mechanism of breastfeeding through direct contact also influences the creation of the baby's immune system.

3. Immunity and Inflammation
Immunity and inflammation play an important role in asthma. Breast milk contains various immunomodulators and anti-inflammatory drugs such as:
  •  α-tocopherol, 
  • β-casomorphins, 
  • prolactin, 
  • soluble toll-like receptor 4, 
  • lactoferrin, 
  • lysozyme, 
  • antioxidants, 
  • cytokines, 
  • secretory IgA. 

Children who are breastfed have a better immune system function and have a lower risk of upper respiratory tract infection. Respiratory tract infection is one of the risk factors for asthma in children. Cortisol, which is formed by contact with the child's mother, also reduces the risk of chronic inflammation and asthma risk.

4. Lung Growth and Lung Function Improvement
Breastfeeding is also found to be related to lung growth and improve lung function. Better lung capacity is a protective factor for asthma. Better lung growth and function are associated with sucking movements when a child is breastfeeding.

Several studies were conducted to determine the breastfeeding effects on children and association with subsequent asthma events. Unfortunately, the researches that have been conducted, including meta-analysis, show inconsistent results.

Scientific evidence of the Relation between Breastfeeding and Asthma events

Research involving nearly 2500 children found that breastfeeding, exclusive or not, had an inconsistent relationship with the incidence of asthma or allergies. In that study, non-exclusive breastfeeding (accompanied by other complementary feedings) did not show a significant association with allergic events such as asthma, eczema, rhinitis, or allergies.

Non-exclusive breastfeeding for 1 or 2, 4, 10, and 18 did not associate with allergic events. However, in other cohorts, breastfeeding at the age of 0-6 months had a risk of asthma at the age of 10 years, two times slower than the group of children who did not get breast milk.

In the analysis, the group of infants who received exclusive breastfeeding for more than 4 months had a protective effect against the incidence of recurrent allergic rhinitis compared to the group without exclusive breastfeeding. Exclusive breastfeeding also showed a protective effect on the prevalence of asthma at the age of 10 years.

A recent study published in 2017 analyzed 840 children. In this study, asthma exacerbations incidence in children with asthma who were breastfed were lower than those of children with asthma without breastfeeding.

In further analysis, breastfeeding for up to 6 months was significantly related to asthma exacerbations. However, breastfeeding for more than 6 months did not show a significant relationship. This study also compared the association of asthma exacerbations with family risk factors for asthma. In children who have family risk factors for asthma, breastfeeding showed a significant relationship to reducing asthma exacerbations, but not in children who do not have family risk factors.

A meta-analysis was carried out in 2012 involving 113 studies. The results mentioned that breastfeeding provided a protective effect on asthma events, especially at 0-2 years old. The protective effect of asthma decreases with age, but it still shows its protective effect until school age.

Another meta-analysis was conducted in 2015 involving 42 studies to determine the effect of breastfeeding on asthma events. In the meta-analysis, the protective effect of breastfeeding on asthma at the age of 5-18 years. The protective effect of breastfeeding has no impact on the group of subject countries.

Researchers conducted analyzes on groups that received exclusive breastfeeding. Researchers found that the incidence of asthma at the age of 5-18 years was not affected by exclusive breastfeeding duration in children. Researchers found a reduced risk of asthma at the age of 5-18 years in children with prolonged breastfeeding. There is a higher risk reduction in populations of countries with low-moderate income. This meta-analysis also found no difference in the effect of breastfeeding on groups of children with family risk factors. 

Limitations of Existing Scientific Evidence

Various reasons can explain this difference in results. Differences in operational definitions by researchers make it difficult to get uniform results. Differences in research methods also affect differences in research results. Some studies also consider several confounding factors in their analysis. Another factor is the paradoxical tendency. There is a tendency for mothers with sicker children, including asthma, to give milk more often and longer to be a confounding factor in the research.

Effect of breastfeeding on other allergic diseases

Several studies have tried to determine breastfeeding's effect on other allergic diseases such as atopic dermatitis or eczema. In a study conducted in the Netherlands, non-exclusive breastfeeding for more than 9 months was associated with a lower risk of eczema in children born to mothers without the risk of allergies or asthma.

Another study conducted in Sweden found that exclusive breastfeeding was not associated with a reduced risk of atopic dermatitis. Another study conducted in South Africa found that breastfeeding for more than 6 months reduced the risk of allergic diseases in general. In children born to parents without the risk of allergies, there was a reverse relationship between breastfeeding duration with the risk of allergic disease in children.

However, other research conducted in the United States found no relationship between breastfeeding and a reduced risk of allergic disease. It was concluded that the study results that looked at the relationship of breastfeeding with other allergic diseases also showed inconsistent results.

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