Gut microbiota not yet considered “adult” at five years old?
It was once thought that the gut microbiota reaches “adult” complexity at the age of 2 or 3. “Not so”, say the authors of a recent study1: at the age of 5, its composition is still different from that of adults, with certain microorganisms essential to health continuing to develop after this age. Hence the importance of taking good care of the gut microbiota throughout childhood!
About this article
It is an undisputed scientific fact that babies in the womb have no gut microbiota: their digestive system is sterile. The microbiota begins to develop from birth through contact with the microorganisms present in the mother’s body during delivery and through contact with the environment. The microbiota gradually becomes stronger and richer in “friendly” bacteria and comes to resemble that of an adult by the time the child is 2 or 3 years old–or so, scientists thought until now. Recently, some research teams have shown that this process may take longer, a finding now supported by a Swedish study which followed more than 470 children from birth to 5 years of age.
Gut microbiota “adult” at age 5? Not quite!
The researchers analyzed the microorganisms present in children’s stool at different ages (at birth, at 4 and 12 months, and at 3 and 5 years) and compared them to samples taken from their mothers and other adults. They began by looking at diversity in the samples. Their first finding was that only a very small minority (3.5%) of the 5 year olds had a gut microbiota as mature as that of the adults.
They subsequently observed how these microorganisms colonized the gut. Roughly speaking, from birth to 4 months, the gut microbiota contains mainly lactic acid bacteria and Bifidobacterium. From 4 months to 1 year, dietary diversification results in a great upheaval: many new microorganisms arrive and settle in, with some microbes multiplying and others becoming less abundant. Between the ages of 1 and 3, this small community develops towards a more “adult” gut microbiota. However, some microorganisms known to be essential for health do not appear until 1 year of age and continue to increase in abundance beyond 3 years of age. Even at 5 years, these microorganisms are still short of adult levels.
For better health, protect the microbiota’s development
The authors of the study stress that the gut microbiota is sensitive to disturbances throughout its development. It is now also known that a gut microbiota imbalance (dysbiosis) in infancy (e.g. due to antibiotic use) can have health repercussions later in life: digestive disorders, excess weight, allergies2,3,4, etc. We also know that a healthy diet during food diversification helps build a healthy gut microbiota.5 Therefore, we should ensure optimal development of the gut microbiota at very least beyond the age of 5 in order to give children every chance of a healthy future.
1. Roswall J, Olsson LM, Kovatcheva-Datchary P et al., Developmental trajectory of the healthy human gut microbiota during the first 5 years of life, Cell Host Microbe; 2021 Mar 23:S1931-3128(21)00100-1
2. Kronman MP, Zaoutis TE, Haynes K et al. Antibiotic exposure and iBD development among children: A population-based cohort study. Pediatrics 2012 ; 130 : e794–e803.
3. Mitre E, Susi A, Kropp LE, Schwartz DJ et al. Association Between Use of Acid-Suppressive Medications and Antibiotics During Infancy and Allergic Diseases in Early Childhood. JAMA Pediatr. 2018 Jun 4;172(6):e180315.
4. Stark CM, Susi A, Emerick J, et al. Antibiotic and acid-suppression medications during early childhood are associated with obesity. Gut 2019 ; 68 : 62–9.
5. Matsuyama M, Morrison M, Cao KAL et al. Dietary intake influences gut microbiota development of healthy Australian children from the age of one to two years. Sci Rep 9, 12476 (2019).