New research shows how birth delivery methods and natural surroundings impact infant gut health, emphasizing the critical role of outdoor time in shaping healthy gut diversity as babies grow.
Study: The role of early life factors and green living environment in the development of gut microbiota in infancy: Population-based cohort study. Image Credit: Design_Cells / Shutterstock
In a recent study published in the journal Environment International, researchers in Finland analyzed the influence of early life factors in shaping the community composition of gut microflora during infancy. High-throughput sequencing alongside multiple metrics of residential greenery revealed the significant role of green environments in determining infants’ gut diversity, particularly during early infancy.
However, the study found that this association was limited to alpha diversity, which measures species richness and diversity, rather than specific microbial community composition. Surprisingly, no such association between residential proximity to green environments and gut floral populations could be established during late infancy. Instead, gut microbial communities were more strongly determined by the time spent outdoors. Notably, birth mode and the presence of siblings were demonstrated to influence infant diversity to substantially greater extents.
These findings help inform pediatricians and (prospective) parents of the early life factors that, despite appearing seemingly disconnected, can have profound and potentially lifelong impacts on their children’s health.
Background
The recent global surge in the prevalence of chronic, non-communicable diseases is partially attributed to the influence of environmental factors and behavioral decisions on gut microbial health. A growing body of evidence links the benefits of ‘healthy’ dietary patterns (e.g., Mediterranean diet) to gut diversity and community composition improvements.
While improvements in diet and other health behaviors can benefit current life gut health, research suggests that the foundations of lifelong gut health are established at birth. The initial gut floral inoculum, primarily derived from infants’ placental connection to their mothers, may be subject to considerable environmentally-mediated variation during early to late infancy, thereby setting the foundation for future gut microbial health.
Unfortunately, most conventional gut microfloral investigations have been carried out on adults. The handful of infant-centric gut microbial studies suffer from the almost ubiquitous demerit of focusing on a single factor (e.g., birth mode or the presence of pets) rather than the holistic and potentially multifaceted impacts of multiple simultaneously acting influences.
About the study
The present study had three main aims: First, to explore the maturation of gut flora across infancy; second, to identify the environmental influences that alter microbial community composition during early and late infancy stages; and third, to investigate associations between metrics of residential greenery and infant gut microbial health.
Study data was obtained from the Steps to Healthy Development of Children (STEPS), a longitudinal cohort comprising Finnish- and Swedish mothers who delivered babies between 2008 and 2010 in a specific Finnish hospital (Hospital District of Southwest Finland). A subset of this 14,946 infant-strong cohort called the ‘intensive follow-up group’ was included as participants in the present investigation. Participants were divided into ‘early’ (0.5-5 months) and ‘late’ (11-17 months) subcohorts.
Data collection included parent/guardian-provided socioeconomic, demographic, and medical records and 1,823 fecal samples for sequence-based infant gut microbiota characterization. Qiagen reagents and protocols were used to extract DNA from fecal samples, and the Illumina MiSeq v3 platform was used for 16S metagenomic sequencing. Reads thus obtained were processed (cleaned and assembled), following which infant-specific microbial community composition was established using the Silva 138.1 prokaryotic SSU taxonomic database.
Additional early life factor data (birth type, gestational age at birth, breastfeeding status, birth weight) were obtained from medical health records and parent-completed follow-up questionnaires. The Population Register Center data for each household was used in tandem with Geographical Information Systems (GIS) data to measure residential vegetation indices – VCDI (an index of vegetation classes) and NI (an index of human land use).
Study findings
The included infant cohort comprised 892 early and 931 late infants, 52% of whom were boys and 46% of whom had older siblings. Over half of the participants’ households were located in non-natural (urban) areas. However, vegetation cover was observed to be moderate or high in most instances. Birth mode data revealed that 11% were delivered via cesarean section, and approximately 10% received maternity hospital-administered antibiotics shortly following delivery.
Analyses of the variables influencing infants’ gut community composition revealed age to be a major determinant. Comparisons between early and late cohorts revealed the former to be dominated by Actinobacteriota (54 %) and substantially more variable than the latter (Firmicutes [59 %]), highlighting that age alone was responsible for explaining around 9% of cohort-wide variation. Previous investigations in the field have rarely included infant-specific age subcohorts, often considering 0-3 years as a single age category. These findings suggest future research needs to account for age subclasses in infant-centric study models.
The analysis showed that birth mode, presence of siblings, and maternal age were the strongest contributors to infants’ gut microbial assemblages. While family income, breastfeeding status, perinatal antibiotic exposure, and outdoor time were significant associations with the gut microbiota, their associations were comparatively weaker.
According to the study’s adjusted models, in early infancy, birth mode (cesarean/vaginal) accounted for 0.5% of the variation in gut microbiota community composition, gradually decreasing to 0.3% in late infancy. The presence of siblings became a more significant factor during late infancy, explaining 0.7% of variability compared to 0.5% in early infancy. Overall, siblings were associated with an increase in gut microbial diversity in both age groups.
Surprisingly, while residential greenery measures established a link between green environments and gut flora, this interaction was primarily limited to early infancy and involved only alpha diversity measures, such as species richness. In contrast, outdoor exposure was a more important predictor of microbiota composition during late infancy.
Conclusions
The present study identifies the factors determining gut microbial diversity during early and late infancy stages and measures their relative impacts. It identifies birth mode, presence of older siblings, and maternal age as the most influential factors, highlighting their roles in shaping the presence and relative abundances of different bacterial populations. Additionally, family income, breastfeeding status, perinatal antibiotic exposure, and outdoor time were found to exert weaker influences on gut flora.
“Moreover, our analysis revealed that associations between residential green environment and gut microbiota alpha diversity were more pronounced in early infancy than in late infancy, indicating a critical period of susceptibility to environmental influences on gut microbiota diversity,” the authors concluded. This underscores the importance of a holistic understanding of early environmental and familial influences on children’s health.
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