We spend time with friends, share meals with family, and sit beside people who matter to us. These moments may seem simple, but something greater could be hidden beneath them. Our bodies might change with every interaction.
Scientists from the University of East Anglia have discovered that social life can influence the composition of bacteria living in the gut. This finding opens up new perspectives in our understanding of health and relationships. The results of the study were published in the journal Molecular Ecology.
A vast number of bacteria reside in the gut. In most cases, they are not harmful. Many of them help the body function better. They break down food, support the immune system, and maintain balance in the body.
This group of bacteria is called the gut microbiome. Its composition is unique to each person. It is influenced by diet and environment, but now scientists see that social interaction also plays a role. Thus, the state of the gut depends not only on what we eat. It also depends on whom we spend time with.
To grasp this idea, researchers studied the Seychelles warbler. This small bird lives on a tiny island and rarely leaves it. This makes it an ideal subject for long-term studies.
Scientists can track every bird, observe its behavior, and study relationships over time. This provides a clear picture of how social life impacts biology.
“To figure out how gut bacteria spread between social partners, we carefully collected bird droppings over several years,” explains co-author of the study, Chuen Zhang Lee. “We gathered hundreds of samples from birds with known social roles—nesting pairs, helpers, and non-helpers living in the same group, as well as in different groups. This allowed us, as a team, to compare the gut microbiota composition of birds that interacted closely at the nest with those that did not.”
The researchers focused on anaerobic gut bacteria, which thrive without oxygen, and this helped them understand how close social interaction could facilitate the spread of these microbes between individuals. The results showed a clear pattern. Birds living together had more similar gut microbiota than those living apart.
This shows that sharing a space matters. But the study goes further. It demonstrates that interaction matters even more. Birds that spent more time together had more similar gut microbiota. This means that daily contact allows bacteria to transfer between individuals.
Not all bacteria behave the same way. Some can survive outside the body, while others cannot. Anaerobic bacteria cannot survive in oxygen. To move from one organism to another, they need close contact. Birds that interacted closely with each other, especially in the nest, were more likely to share these bacteria. Such birds fed their chicks, stayed near each other, and frequently communicated.
“We found that the more you interact with others, the more similar your anaerobic gut bacteria are,” says Lee.
This shows that the driving force behind this exchange is not just proximity, but specifically the nature of that proximity.
Within groups of birds, some individuals act as helpers. These helpers assist in raising chicks. This role ensures they have constant contact with others. As a result, helpers share more gut microbiota with the group. Their microbiome becomes more similar to that of those around them. This demonstrates that behavior and responsibilities within a group can influence biological processes.
Living together, cooking meals together, or even sitting in close proximity to each other create conditions for bacteria to spread between people.
“Whether you live with a partner, a roommate, or your family, your daily interactions—from hugs and kisses to cooking together—may contribute to the exchange of gut microbes,” says Lee.
These small actions happen every day. Over time, they can affect the gut microbiome.
The idea of exchanging bacteria might seem strange at first, but not all bacteria are harmful. In fact, many of them help the body function better.
Some bacteria aid digestion, others protect against disease and maintain balance in the body. So, sharing beneficial bacteria could even promote better health within a family. This study shows that human relationships extend beyond emotions. They also subtly influence the body.
The people around us can affect our health at a level we cannot see. Our daily habits and our relationships all play a role. Our relationships can impact not only our day.
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