Risk Factors for Gut Dysbiosis in Early Life

Abstract

Dysbiosis refers to a reduction in microbial diversity, combined with a loss of beneficial taxa, and an increase in pathogenic microorganisms. Dysbiosis of the intestinal microbiota can have a substantial effect on the nervous and immune systems, contributing to the onset of several inflammatory diseases. Epidemiological studies provided insight in how changes in the living environment have contributed to an overall loss of diversity and key taxa in the gut microbiome, coinciding with increased reports of atopy and allergic diseases. The gut microbiome begins development at birth, with major transition periods occurring around the commencement of breastfeeding, and the introduction of solid foods. As such, the development of the gut microbiome remains highly plastic and easily influenced by environmental factors until around three years of age. Developing a diverse and rich gut microbiome during this sensitive period is crucial to setting up a stable gut microbiome into adulthood and to prevent gut dysbiosis. Currently, the delivery route, antibiotic exposure, and diet are the best studied drivers of gut microbiome development, as well as risk factors of gut dysbiosis during infancy. This review focuses on recent evidence regarding key environmental factors that contribute to promoting gut dysbiosis.

Keywords: atopy; gut dysbiosis; gut microbiome; inflammatory disease.

Figure 1

The developing gut microbiome and major influencing environmental factors. Alpha-diversity (diversity within one sample) increases as the gut microbiome develops. The beta-diversity (diversity between samples) decreases with age, indicating that gut microbiome differences are most variable between people during infancy, and become more similar n adulthood. The first three years of life represent a period of heightened plasticity where gut microbiome development is easily impacted by environmental factors.

Figure 2

The gut-brain-axis showing the bidirectional relationship between the gut microbiome and the nervous system. The gut microorganisms ferment dietary fibre which produces SCFAs. The SCFAs are proposed to enter the circulatory system and into the brain via the blood brain barrier.