Living with other people may have a subtle effect on your gut bacteria, according to new research from the University of East Anglia.
A study of small island birds found that individuals shared more gut microbes with the individuals they came in contact with most frequently. Researchers say this same effect is very likely occurring in humans.
Previous studies in humans have suggested a similar pattern. Couples and people who have lived together for many years tend to have more similar gut microbiota than unrelated people, even if they don’t share the same diet. The new findings provide strong evidence that close social contact itself, rather than just the shared environment, plays an important role in the exchange of gut bacteria.
Study shows social contact shapes gut bacteria
The study focused on the Seychelles warbler, a small songbird that lives on Cousin Island in the Seychelles.
Scientists collected fecal samples from birds and used them to study the gut microbiome, the community of beneficial bacteria in the digestive system.
Dr. Chuen Zhang Lee from UEA’s School of Biological Sciences conducted the research as part of his doctoral program.
“To find out how gut bacteria spread between social partners, we spent several years carefully collecting bird poop,” he said. “We collected hundreds of samples from birds with known social roles: pairs living in the same group or different groups, helpers and non-helpers.”
“This allowed us to compare the gut bacteria of birds that interact closely in the nest with those that do not.
“We studied their anaerobic gut bacteria, which thrive in the absence of oxygen.
“And it gave us valuable insight into how social bonds facilitate the transmission of gut bacteria.”
The island environment provides unique research conditions
Cousin Island provided an ideal natural environment for this long-term study.
Senior researcher Professor David S. Richardson explained: “Cousin Island is small and isolated, and the warblers never leave the island. This means all the birds on the island are individually marked and can be tracked throughout their lives.”
“This provides an incredible opportunity for scientists to study lifelong biological processes in the wild.”
Each bird is fitted with colored foot rings that allow researchers to monitor their behavior, health and genetics over many years. This creates conditions similar to a controlled laboratory population while reflecting a real-world environment.
“It gives us the best of both worlds,” Professor Richardson said. “We can study animals that live a natural life with a natural diet and gut bacteria, while collecting detailed data from known individuals.”
Close relationships facilitate microbial sharing
The results showed a clear pattern. Birds that spent more time together had more similar gut bacteria, especially anaerobic microbes that can only survive in low-oxygen conditions.
“We found that the more social you are with other people, the more likely you are to share similar anaerobic gut bacteria,” Dr. Lee said.
“Birds that spend a lot of time together in the nest – the breeding couple and their devoted helpers – share many of these gut bacteria, which can only be spread through direct, close contact.
“These anaerobic microorganisms cannot survive outdoors, so they don’t float around in the environment. Instead, they move between individuals through intimate interactions or shared nests.”
What this means for human gut health
Researchers believe these findings shed light on what goes on in human homes.
“Whether you live with a partner, roommate, or family member, daily interactions such as hugs, kisses, and sharing food preparation space can encourage the exchange of gut microbes,” Dr. Lee said.
“Anaerobic bacteria are some of the most important for digestion, immunity, and overall health. Once in the gut, they thrive in the absence of oxygen and often form stable long-term colonies. This means the people you live with may be subtly shaping the microscopic ecosystem inside your body.”
“Translated into human terms, this means that having a cozy night in, sharing laundry, and even sitting close together on the couch can quietly bring our microbiomes closer together.
“Sharing beneficial anaerobic bacteria may strengthen immunity and improve digestive health across the household,” he added.
The research was led by UEA, in collaboration with researchers from Norwich Research Park, including the Microbial Interaction Centre, Quadrum Institute and Earlham Institute, as well as the University of Sheffield, the University of Groningen (Netherlands) and Nature Seychelles.
Research results will be published in a magazine molecular ecology “Social structure and interactions differentially shape aerobic and anaerobic gut microbiota in co-breeding species,” they wrote in their paper.
