In 1989, an epidemiologist in Britain, David Strachan, observed that babies born into households with lots of siblings were less likely than other babies to develop allergies and asthma. The same proved true of babies who spent significant time in day care. Dr. Strachan hypothesized that the protection came from experiencing an abundance of childhood illnesses.
Dr. Strachanâ€™s original hygiene hypothesis got a lot of press. . . Less publicized was the decade-long string of follow-up studies that disproved a link between illnesses and protection from inflammatory disorders like allergies and asthma. If anything, studies showed, early illness made matters worse. . .
Still, Dr. Strachanâ€™s original observation was confirmed â€” as a group, babies in large families and day care are less likely to develop allergies and asthma than are children born into smaller families and kept at home. The same protective effect can be seen in children born on farms and in areas without public sanitation.
But the link isnâ€™t disease-causing germs. Itâ€™s early and ample exposure to harmless bacteria â€” especially the kinds encountered living close to the land and around livestock and other young children. In other words, dirt, dung and diapers. Just as disease-causing microbes clearly bring on inflammation, harmless microorganisms appear to exert a calming effect on the immune system.
No mention of fermented food.
Thanks to Michael Bowerman.