Origins of Hygiene Hypothesis

A recent NY Times article explains the background of the ‘hygiene hypothesis’ and how it has held up remarkably well as a likely factor in the rising number of allergic and immune-mediated diseases.

Link: Your Environment is Cleaner. Your Immune System Has Never Been So Unprepared

An excerpt:

The British Journal of Homeopathy, volume 29, published in 1872, included a startlingly prescient observation: “Hay fever is said to be an aristocratic disease, and there can be no doubt that, if it is not almost wholly confined to the upper classes of society, it is rarely, if ever, met with but among the educated.”..

In November 1989, another highly influential paper was published on the subject of hay fever. The paper was short, less than two pages, in BMJ, titled “Hay Fever, Hygiene, and Household Size.”

The author looked at the prevalence of hay fever among 17,414 children born in March 1958. Of 16 variables the scientist explored, he described as “most striking” an association between the likelihood that a child would get hay fever allergy and the number of his or her siblings.

It was an inverse relationship, meaning the more siblings the child had, the less likely it was that he or she would get the allergy…The paper hypothesized that “allergic diseases were prevented by infection in early childhood, transmitted by unhygienic contact with older siblings, or acquired prenatally from a mother infected by contact with her older children…

[To avoid disease] we started washing our hands and took care to avoid certain foods that experience showed could be dangerous or deadly…Particularly in the wealthier areas of the world, we purified our water, and developed plumbing and waste treatment plants; we isolated and killed bacteria and other germs…

What does the immune system do when it’s not properly trained?

It can overreact. It becomes aggrieved by things like dust mites or pollen. It develops what we called allergies, chronic immune system attacks — inflammation — in a way that is counterproductive, irritating, even dangerous.

The percentage of children in the United States with a food allergy rose 50 percent between 1997–1999 and 2009–2011, according to the Centers for Disease Control and Prevention…

There are related trends in inflammatory bowel disease, lupus, rheumatic conditions and, in particular, celiac disease. The last results from the immune’s system overreacting to gluten..

And even doctors have been wrong….They have vastly overprescribed antibiotics. These may be a huge boon to an immune system faced with an otherwise deadly infection. But when used without good reason, the drugs can wipe out healthy microbes in our gut.

My take: With the increasing frequency of many diseases, there has to be environmental influences since our population genetic makeup does not change rapidly. Thus factors like infections, microbiome and exposure to antibiotics are likely important in the changing epidemiology.

Related blog posts:

The Rise of Eosinophilic GI Diseases –Not Likely Connected to Helicobacter Pylori

A recent prospective case-control study (J Molina-Infante et al. Am J Gastroenterol 2018; 113: 972-9 -thanks to Ben Gold for this reference) examined the potential connection between Helicobacter pylori and eosinophilic GI diseases.  They examined 808 individuals (404 cases of eosinophilic esophagitis [EoE], 404 controls). Key findings:

  • H pylori prevalence was not different between cases and controls (37% vs. 40%, odds ratio 0.97).  The authors conclude that H pylori which has declined in prevalence globally is not inversely associated with EoE as had been suggested in some previous reports

In an associated editorial, (pg 941-4), the authors note that there has been a dramatic increase in atopic diseases over the past 30 years.  One hypothesis has suggested that these epidemiologic changes are related to a changing microbiome.  This in turn may be related to frequent antibiotic usage.  An example of the proliferation of antibiotics: “20-25% of Swedish adults receive an antibiotic prescription annually.”

While H pylori may be a biomarker associated with poor hygiene/less antimicrobial exposure, it does not appear to be directly related to EoE.  The authors indicate that until we have a better understanding, “in the meantime attention to healthier diets and minimizing antibiotic exposure may optimize public health in terms of atopic disease risk.”

My take: Since our genetics do not change quickly, the dramatic changes in disease frequency of conditions like EoE and Crohn’s disease must be influenced by environmental exposures.  How to lower the risk of these conditions remains uncertain.

Related blog posts:

Not a joke –WIFI hotspot at Sunshine Meadows, Banff National Park

NYT: Educate Your Immune System

A recent commentary updates the concept of the hygiene theory and how our lack of exposures to a ‘dirtier’ environment when we are younger can make us more prone to autoimmune diseases, including celiac disease, diabetes, and multiple sclerosis.

Here’s the link: Educate Your Immune

Here’s an excerpt:

People living just over the border in Russian Karelia, as the region is known, have the same prevalence of genes linked to autoimmune disease [as in Finland]. They also live at the same latitude and in the same climate. And yet they have a much lower vulnerability to autoimmune disease. Celiac disease and Type 1 diabetes occur about one-fifth and one-sixth as often, respectively, in Russian Karelia as in Finland. Hay fever and asthma, allergic diseases that also signal a tendency toward immune overreaction, are far less common.

So in a follow-up study, the results of which appeared last month in the journal Cell, Dr. Xavier and his colleagues followed 222 children who were genetically at risk of developing autoimmune diabetes. The newborns were equally divided among Finland, Russia and Estonia, where the prevalence of Type 1 diabetes is on the rise, but still well below Finland’s.

Autoimmune diabetes can be predicted, to some degree, by the appearance of certain antibodies in the bloodstream that attack one’s own tissues. After three years, 16 Finnish children and 14 Estonian children had these antibodies; only four Russian children did. And when the scientists compared the children’s microbiomes in the three countries, they found stark differences. A group of microbes called bacteroides dominated in Finnish and Estonian infants. But in Russia, bifidobacteria and E. coli held sway….

Russian kids have more fecal oral infections, such as hepatitis A, suggesting more sharing not only of pathogens, but of microbes that may benefit health. And previous studies have found that Russian homes harbor a richer and more diverse community of microbes than Finnish ones….

The world today is very different from the one our immune system evolved to anticipate — not just in what we encounter, but in when we first encounter it. Preventing autoimmune disorders may require emulating aspects of that “dirtier” world.

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