What is already known on this topic
Infancy is a key period for several biological processes, including the development of the gut microbiota. Many studies have focused on the gut microbiota in early infancy, but little is known about the development of gut microbial communities after the first two to three years after birth.
What this research adds
By analyzing the gut microbiota from more than 450 Swedish children, researchers have found that the community of gut-dwelling microbes reaches an adult-like composition by the time children are five years of age, but the normal gut microbiota develops differently in different individuals. Although many of the bacteria dominating the adult gut microbiota — including some that have been associated with human health — are established at three years of age, the team identified several less abundant microbes whose levels are increasing up to five years of age.
The findings show that several bacteria associated with human health are acquired late in childhood — albeit with different developmental dynamics.
Infancy is a key period for several biological processes, including the development of the gut microbiota. Now, a study shows that many bacteria associated with human health may not reach their adult abundance until five years of age in some people.
The findings, published in Cell Host & Microbe, highlight the importance of taking microbiota dynamics into account, the researchers say. “We hope to highlight that the gut microbiota continues to develop during childhood,” says senior study author Fredrik Bäckhed at the University of Gothenburg. “Our findings underscore the possibility that the microbiota may be particularly sensitive to disturbances during this early establishment, which may have profound effects on health later in life,” he says.
Several studies have focused on the gut microbiota in early infancy, but little is known about the development of gut microbial communities after the first two to three years after birth. To address this gap in knowledge, Bäckhed and his colleagues analyzed the microbiota from 471 Swedish children.
The researchers followed the children from birth to five years of age, collecting fecal samples after four months, one year, three years, and five years after birth. Then, they profiled the microbes present in those samples as well as the bacteria present in fecal samples from the children’s mothers and a group of adult Swedish individuals.
The most dramatic changes in microbiota composition occurred between four and twelve months of age, the researchers found. Several bacteria that are commonly found in adults, including Faecalibacterium, Akkermansia, and Ruminococcus, appeared around the time children turned one year of age and began to eat solid food. However, the abundance of these bacteria increased further as the children grew older.
The abundance of bacteria such as Methanobrevibacter and Christensenellaceae, which have been linked to metabolic health, was lower in five-year-olds that it was in adults. Instead, the levels of Ruminococcus gnavus were lower in adults than in five-year-olds, the researchers found. R. gnavus has been associated with conditions such as obesity and inflammatory bowel diseases.
Over the observation period, different bacteria increased in abundance and stabilized at various time points after birth, the team found. What’s more, children who weighed less than expected had a more immature gut microbiota at one year of age than children with average weight. Children with lower weight gain also had reduced levels of Faecalibacterium, which has been linked to metabolic health.
Further analyses confirmed previous findings showing that C-section was associated with lower microbial diversity at four months, and the abundance of 25 types of bacteria differed in kids born with C-section compared to those born vaginally. However, the effect of C-section on gut microbiota composition appeared to normalize within three to five years after birth.
The researchers note that it’s unclear whether these differences in microbiota composition could influence future metabolic conditions. “Future, larger studies are required to identify potential time windows when the gut microbiota may be particular important for the development of diseases in humans,” Bäckhed says. However, the authors add, the study offers a reference point for the normal development of the gut microbiota in infancy and early childhood.