The results of this study suggest that breast feeding may offer protection against the development of CD. Meta‐analysis of data of four studies indicated that children being breast fed at the time of gluten introduction had a 52% reduction in risk of developing CD compared with their peers who were not breast feeding at the time of gluten introduction. With the exception of one small study,6
all the studies included in the review also showed a statistically significant association between increasing duration of breast feeding and reduced risk of CD. The sample size of that study was, however, quite small (see table 1), and there was a risk of a type II error. We cannot tell, from the results of the primary studies, whether breast feeding provides a permanent protection against the development of CD or whether the practice only delays the onset of symptoms. All the included studies, except Ascher et al
had used healthy children without symptoms of CD as controls without subjecting them to small intestinal biopsies. CD can be notoriously asymptomatic and the absence of symptoms does not necessarily mean absence of the disease.
What this study adds
- Breast feeding at the time of gluten introduction significantly reduces the risk of coeliac disease. Increasing duration of breast feeding is associated with a reduced risk of coeliac disease
- It is not clear from the primary studies whether breast feeding only delays the onset of symptoms or provides a permanent protection against the disease
The actual mechanism through which breast milk protects against the development of CD is unclear. It could be that continuing breast feeding at the time of weaning limits the amount of gluten that the child receives, thereby decreasing the chances of the child developing symptoms of CD. Ivarsson et al
found that children with CD received larger initial amounts of flour compared to controls.3
Another mechanism through which breast milk could protect against CD is by preventing gastrointestinal infections in the infant. Breast milk is known to significantly protect against a number of infections including gastroenteritis.24
Infections of the gastrointestinal tract in early life could lead to increased permeability of the intestinal mucosa, allowing the passage of gluten into the lamina propria. Gut infections are also known to increase tissue transglutaminase expression and this could favour the generation of deamidated gluten peptides,25
triggering CD in susceptible individuals.
Juto et al
have suggested two other possible mechanisms by which breast milk could confer protection against CD.26
Firstly, human milk IgA antibodies may diminish immune response to ingested gluten by mechanisms such as agglutination of the antigen to immune complexes on the mucosal surface so that uptake is prevented. Secondly, the immune modulating property of human milk may be exerted through its T‐cell specific suppressive effect as shown by experiments on peripheral lymphocytes stimulated with phytohaemagglutinin, OKT3, and alloantigens.27
The results of this study are subject to limitations. The included studies were case‐control studies, which are subject to recall bias. Misclassification of the duration of breast feeding and of the age of introduction of gluten was likely to occur. If, for instance, parents of children with CD could recall more accurately that their children were not breast feeding at the time of gluten introduction, bias could result which would tend to inflate the association in favour of breast feeding.
Case‐control studies are also susceptible to bias because other risk factors of CD could be unbalanced across children who were breast fed and those who were not. While the individual studies tried to control for a number of potential confounding factors such as age, sex, and area of residence, it is likely that a number of other confounding factors, such as socioeconomic status, could have been unbalanced across children who were breast fed and those who were not.
The only study that controlled for HLA genotype did not find a significant difference between the groups with regard to duration of breast feeding but as earlier stated, the sample size of this study of only eight cases was so small that a type II error was likely to have occurred.6
Breast feeding may offer protection against the development of CD. Breast feeding during the introduction of dietary gluten, and increasing duration of breast feeding were associated with decreased risk of developing CD. It is, however, not clear from the primary studies whether breast feeding delays the onset of symptoms or provides a permanent protection against the disease. Long term prospective cohort studies are required to investigate further the relation between breast feeding and CD.