Our obsession with hygiene and sterility has caused us to lose touch with many bacteria that normally help our immune systems develop resistance to disease-causing bacteria. Now, another study confirms this notion, asserting that it is the reason some people develop inflammatory bowel diseases like ulcerative colitis and Crohn’s disease. But specifically, it found that people who grow up on farms with livestock, as opposed to an urban setting, are 50 percent less likely to develop these diseases. 

"It is extremely exciting that we can now see that not only allergic diseases, but also more classic inflammatory diseases appear to depend on the environment we are exposed to early in our lives," said Vivi Schlünssen, associate professor of public health at Aarhus University, in a press release. The study was published in the European Journal of Epidemiology.

The Hygiene Hypothesis

The "hygiene hypothesis" is based on the belief that a lack of exposure to allergens, infectious pathogens, and symbiotic organisms like gut flora, supress the natural development of our immune system, making us more susceptible to conditions like asthma, eczema, and other autoimmune disorders and allergies. Inflammatory bowel disease (IBD) is also thought to be an autoimmune reaction, where the body mounts an immune attack, even in the absence of an invading organism.

To test the relation between hygiene hypothesis and IBD, the researchers made use of a cohort study that involved 10,864 subjects who were born between 1945 and 1971 in various European countries, and had completed questionnaires. They discovered that people born after 1952, who had spent the first five years of their lives on a livestock farm, were better protected against diseases of the digestive tract than than those who were born earlier. In fact, results from the oldest age group seemed to show that it made no difference whether the subjects grew up in a town or on the countryside. They attributed this findings to a lower microbial diversity.        

"This leads us to believe that there is a correlation between the rise in inflammatory bowel diseases and increasing urbanization, given that more and more children are growing up in urban settings," said Signe Timm, co-author of the study from Aarhus University, in the release. "We know that development of the immune system is finalized in the first years of our lives, and we suspect that environmental influences may have a crucial effect on this development. The place where you grow up may therefore influence your risk of developing an inflammatory bowel disease later in life." 

Timm said that the the reason for increased incidences of IBD come partly from growing differences in microbial environments between cities and farm areas. "We are exposed to far fewer different bacteria in urban environments today than we were previously. This may in part explain our findings," he said. 

Can Protection Be Passed On?

According to the Crohn's & Colitis Foundation of America, an estimated 1.4 million people are diagnosed with IBD before they turn 30. That begs the question: Can immunity to IBD be passed down from someone who lived on a farm to their children? While it is known that disease causing genes can be inherited, it has yet to be established whether protective genes against autoimmune disorders can be inherited. For this, Timm and her team plan to get in touch with the participants' 20,000 or so children. 

Source: Timm S, Svanes C, Janson C, et. al, Place of upbringing in early childhood as related to inflammatory bowel diseases in adulthood: a population-based cohort study in Northern Europe. European Journal of Epidemiology. 2014.