"In the past 10 years, we have been realizing that breast-feeding brings much more than we thought," said Dr. Lars Hanson, from the University of Goteborg in Sweden. "Not only are some of the mother's defenses passed on to the child, but breast-feeding actually seems to activate something in the baby's own defense system."

Hanson, Dr. Sven-Arne Silfverdal, from the Orebro Medical Center Hospital in Sweden, and colleagues looked at children under age 6 who had been seriously ill with Haemophilus influenzae type b (Hib), a type of bacteria that can cause pneumonia, meningitis, and other potentially life-threatening infections. The children became ill in the late 1980s and early 1990s, before a Hib vaccine became available in Sweden.

The researchers found that youngsters 18 months or older who had been breast-fed exclusively for more than 13 weeks (average 19 weeks) had a stronger immune response to Hib than those breast-fed exclusively for less than 13 weeks (average 5 weeks). There was no difference in immune response in children under 18 months of age, according to the report published in the Pediatric Infectious Disease Journal.

Vaccination against Hib now exists in most countries, but the bacterium still poses a threat in poor countries with inadequate healthcare programs and vaccination, according to the report. Moreover, this report could be used as a model to study the protective benefits of breast-feeding against other types of diseases and infections, Hanson said.

"Convincing studies also demonstrate significant protection against diarrhea, respiratory tract infections, otitis media (ear infections), or urinary tract infection, for instance," he said.

In previous studies, Silfverdal's team also suggested that this immune system enhancement could last over the years, beyond the period of breast-feeding itself.

"We don't really understand how that might work, but the information is growing that longer periods of breast-feeding may afford more complete protection not only against certain diseases that may occur during breast-feeding, but also against disorders that surface long after breast-feeding is over," said Dr. Armond Goldman, from the University of Texas Medical Branch in Galveston, who was not involved in the study.

The point when a child no longer requires this immunological support via breast-feeding has not yet been established, according to Hanson, but "the more the better and the longer the better," he said.

Current recommendations suggest that exclusive breast-feeding should be continued for the first 4 to 6 months of life and up to a year if possible, according to Goldman, which is not always an easy recommendation to follow in the US.

"It's easy to say that people should be child-centered," he said, "but there are obvious socioeconomic factors that have to be taken into consideration and mothers also need an adequate environmental support to be able to breast-feed. Many factors come into play that make breast-feeding difficult."

SOURCE: The Pediatric Infectious Disease Journal 2002;21:816-821.