Mencius, a Chinese philosopher, wrote a handful of centuries ago that “friendship is one mind in two bodies.” Modern science could add another element: friendship is also a microbiota in two bodies. A study has found that the more people interact, the more similar the composition of the microorganisms living in their intestines becomes, even if they do not live in the same household. The investigation, recently published in the magazine Naturealso ensures that an individual’s microbiome is determined not only by their closest social contacts, but also by the connections of these contacts. That is, the friends of your friends.
To know the details of this investigation you have to take a trip to the western heart of the Honduran jungle. It was in this Caribbean country where scientists from Yale University worked for ten years until they recruited a group of 1,787 adults, spread across 18 isolated villages, to donate a sample of their feces. All participants had a traditional diet and practically did not consume antibiotics or other medications. Nicholas Christakis, lead author of the study, explains that they were “very lucky that the participants were helpful and engaged.” The scientists needed to be able to trace each of the volunteers’ contacts with certainty, something that would have been much more complicated to do in cities like Madrid or Barcelona. The towns of Honduras, in this case, were perfect.
Before continuing to advance with the results of this research, it is worth explaining what the microbiota is and why it is important. Francisco Guarner, director of the Digestive System Research Unit at the Vall d’Hebron General Hospital in Barcelona, has a definition: “It is the bacteria communityviruses and fungi that colonize the digestive tract. We could think of it as another organ of the human body, a set of biological capacities that help the survival of an individual.” Although this organ It lives within us, it functions under its own rules and hierarchies. It is organized in its own way and it is not easy to manipulate it. “It is essential for the digestion of food. It provides us with many enzymes and metabolic pathways that humans do not have,” adds the expert. Thanks to the microbiota we can, for example, digest fiber. They are also essential for the development of a balanced immune system.
For decades, science has explored the composition of the microbiota to understand how it is generated in each person. Mireia Vallés Colomer, director of the Microbiome Research Group at Pompeu Fabra University, details that vertical transmission had been, until now, the most likely explanation. “We receive these microorganisms, in large part, from our mothers, through childbirth and breastfeeding. We also share bacteria that our grandmother passed to our mother,” he details. However, the new study ventures that the microbiota changes throughout life, and that those largely responsible for these changes are our social contacts. A horizontal transmission.
“We were very surprised by the reach of microbes that networks of people share. In fact, we can predict who your friends are based on how similar the microbes in your stool are to theirs,” says Christakis. Data suggests that people living in the same house share up to 14% of the microbial strains in their intestines. While those who do not live together, but usually spend time together, share 10%. The research has also been able to determine that individuals who live in the same town, but who do not usually interact too frequently, share only 4%. There is, the authors say, a chain of transmission because friends of friends share more strains than would be expected by mere chance.
The transmission method
There is a question that continues to swirl around this research and that is to understand how strains are transmitted bacteria from one microbiota to the other. “We do not have a conclusive answer about how this transmission occurs,” says Vallés. And he adds: “What is hypothesized is that what reaches the intestine has to pass through the mouth. “Many bacteria in the microbiome don’t tolerate direct contact with oxygen for very long, so close contact is needed, but we don’t know exactly what that looks like.”
Guarner, however, details that “the fecal-oral route “It seems to be the most important transmission vector.” That is to say, although we clean ourselves and more or less control our hygiene, in some previous studies it has been detected that the bacteria that are typically found in the intestine also appear on the hands. This is how they then reach the mouth.
Some of the bacteria manage to survive this journey from the intestine because they travel in the form of spores, similar to those of fungi. “With this transmission mechanism it does not have to be extremely direct contact, it can be through a towel or clothing,” details Guarner.
There is no need to be alarmed. This transfer of microorganisms It is what, in some way, keeps us alive. So much so, that new lines of research on the relationship between microbiota and health suggest that a healthy and fit community of microorganisms has an impact on several aspects of our well-being.
Some researchers are trying to establish a direct relationship between the microbiota and non-communicable diseasessuch as cardiovascular diseases, diabetes and even depression. Guarner explains: “This is still a bit speculative, but normally what happens is that these types of diseases are associated with a poor microbiome.” Vallés contributes that “it has been observed that people with the so-called ‘modern diseases’ suffer an alteration in the composition of their microbiome.” But it is not that there is a particular bacteria responsible for these diseases, but rather it is the loss of diversity in general that worsens the state of health. In this case, the research opens the door to continue analyzing whether these non-communicable diseases, in fact, do have a transmissibility factor. And if an entire community of people has a weakened microbiota, these diseases could proliferate more easily among that population.
“We already knew that the social environment has a very important effect on general health. Now we see that it also helps shape our microbiome and this is something we can no longer ignore. We cannot study humans as if they lived in isolation, but we have to do it together with the community they make up,” Vallés summarizes.