The contrasting human gut microbiota in early and late life and implications for host health and disease

The gut microbiota plays a significant role in health and development from birth and continues to affect several processes throughout life and into old age. During both infancy and old age, the trajectory of the gut microbiota changes with contrasting consequences at both stages for the host. The infant gut is unstable, and colonization is influenced by a variety of perinatal and postnatal factors. Many of these factors can contribute to an altered microbiota profile in infancy which can be associated with negative consequences later in life such as allergies, obesity, and neuropsychiatric disorders. The late-life gut microbiota is influenced by physiological changes within the host, illness, diet and lifestyle that impact its composition and functionality. Indeed, reduced microbial diversity, loss of beneficial microorganisms and increased pathobionts are key signatures of the elderly microbiome. Such changes have been associated with degenerative diseases including inflammaging, Alzheimer's disease, Parkinson's disease, and increased risk of infection with Clostridioides difficile. Here, we examine early- and late-life factors that contribute to contrasting gut microbiota disturbances and the consequences associated with these disruptions. Finally, we provide compelling evidence of nutritional and probiotic/prebiotic interventions that may help alleviate the effects of gut microbiota changes into old age.