Subjects. Sera were obtained from 74 healthy children, below 6 years of age, recruited as controls in a case control study. Duration and mode of breastfeeding were registered. Frequent infections as stated by parents and levels of antibody to Haemophilus influenzae type b (Hib) were studied in relation to the duration of exclusive breastfeeding.
Results. Duration of exclusive breastfeeding emerged as a protective factor against frequent non-invasive and non-specific infections in all children with an OR of 0.92 (0.86-0.98), adjusted for passive smoking and sex. After stratification for age the OR decreased to 0.87 (0.76-1.0) in children less than 18 months indicating a stronger protective effect by exclusive breastfeeding against frequent non-invasive infections in younger children compared to older ones. In the younger children sex was the only significant factor associated with the anti-Hib IgG1 and IgG2 antibody levels. Duration of exclusive or any breastfeeding, used either as a dichotomised or a continuous variable, did not show any significant influence on the antibody levels in the younger children. In children ≥ 18 months of age the regression model for anti-Hib IgG2 antibody level was close to significance (p=0.052) but with only a very low R2 around 0.07. When frequent infections or passive smoking was added as an explanatory variable, duration of exclusive breastfeeding became significant (p=0.036) but still with a low R2 Duration of exclusive breastfeeding was significantly related to the anti-Hib IgG2 antibody level in older children without frequent infections. Expression ofldiotype-1 (Id-1) antibodies increased with age in contrast to Id-2 antibodies that were found only in children ≤ 24 months of age, but the levels of neither Id-1 nor Id-2 antibodies were related to duration of breastfeeding or passive smoking. In older children, those without frequent infections showed higher levels of antibodies expression Id-1 than children with frequent infections.
Discussion. Human milk contains oligosaccharides, leucocytes (granulocytes, macrophages and lymphocytes), hmmones, cytokines, growth factors and other substances that may protect against infection or stimulate the proliferation and the development of the innate and adapted immune system including a stimulatory effect on the anti-Hib antibody response. The distributions of Id-1 and Id-2 were related to age and the IgG2 anti-Hib antibody levels.
Conclusion. This study shows that exclusive breastfeeding is likely to have a protective effect against frequent non-invasive infections. It also shows that breastfeeding seems to enhance the anti-Hib IgG2 antibody production in healthy children.