Impact of maternal smoking on the infant gut microbiota and its association with child overweight: a scoping review

Background Childhood obesity is a growing public health concern with evidence demonstrating that while infant exposure to maternal smoking is linked to low birth weight at birth, there is a rapid catch up in weight and increased risk of obesity in later life. This scoping review aims to synthesize up-to-date evidence on the impact of maternal smoking on the infant gut microbiota and its association with child overweight. Methods We conducted a PRISMA-compliant scoping review. Primary population-based cohort studies published between 1900 and April 2018 were included. Relevant publications were retrieved from seven databases: PubMed, Medline, Embase, Scopus, Biosis, Cochrane library, and Web of Science Core Collection. Results A total of three prospective cohort studies were included which utilized high-throughput 16S rRNA gene sequencing to assess the gut microbiota and included a total of 1277 infant/neonatal participants. Neonates exposed to environmental smoke had a higher relative abundance of Ruminococcus and Akkermansia. Infants exposed to environmental smoke during pregnancy or postnatally were found to have increased gut bacterial richness, particularly Firmicutes at 3 months of age, while 6-month-old infants born to smoking mothers had an increased abundance of Bacteroides and Staphylococcus. Elevated Firmicutes richness at 3 months of age was associated with elevated odds of child overweight and obesity at 1 and 3 years of age. Conclusion The limited evidence to date warrants further large scale, longitudinal studies to explore the impact of maternal smoking and environmental tobacco smoke on the infant gut microbiome and its relation to child overweight.