Shaping Microbiome in the First 1,000 Days of Life

Evidence from the Developmental Origins of Health and Disease (DOHaD) theory has pointed out biological mechanisms supporting the intergenerational nature of non communicable diseases (NCDs), which are an increasing public health problem in many countries. Furthermore, scientific evidence confirms that the events occurring in the early stages of life play a critical role in fostering the development of chronic diseases (e.g. overweight and obesity, allergies, cardiovascular and metabolic diseases, neurocognitive impairment and cancers), throughout the life-course, indicating the high relevance of "the maternal environment" impact on the life of the future child. This crucial window goes from the conception to the two years of life, and it is known as 'first thousand days'.

Nutritional status during pregnancy is one of the crucial determinants in modulating the characteristics of the "maternal environment" in which the foetus originates and develops. Therefore, adequate nutrition just before conception, during pregnancy, infancy and early childhood is essential to ensure growth, health, and development of children to their full potential.

Epigenetic links have been confirmed in mice between the prenatal diet and the increased incidence of obesity, type 2 diabetes and other metabolic associated conditions in their offspring. However, specific epigenetic regulation mechanisms are still unclear. Recently, an increasing number of animal and human studies have proposed the hypothesis that the gut microbiota may be considered an important mediator of vital microbiome-host interaction(s) under health or disease conditions. Moreover, microbiota has been shown to pass features from one generation to the next via maternal contact; in fact, recent observation of microbial presence in placenta, meconium and amniotic fluid has suggested a significant interplay between the environmental microbes and the developing gastrointestinal tract of the fetus even before delivery. Thus, the alteration of microbiota composition, driving to increased long-term susceptibility to diseases, can begin early in life.

Examination of the neonatal gut microbiome immediately after delivery revealed that it varied by virtue of maternal gestational diet suggesting that the colonization of the infant gut is likely to occur prior to parturition.

During the first months after birth, the bacterial flora in the gut is known to be affected by many factors, including mode of delivery, use of antibiotics or probiotics, geographical location, type and time of feeding.

Moreover, maternal exposures during pregnancy to several environmental chemicals are known to induce perturbations in the composition of the gastrointestinal microbiome. Among these substances, endocrine disruptor chemicals (EDCs), such as phthalates, bisphenol and hydroxypyrene, which can be found in oil and water resistant textile coatings, non-stick cookware, food container coatings, floor polish, fire-fighting foam, and industrial surfactants, are a class of suspected obesogenic contaminants persisting in the environment and humans. EDCs have been also detected in cord blood samples, suggesting that exposure starts prenatally and early life EDC exposures may perturb neuroendocrine systems involved in growth, energy metabolism, appetite, adipogenesis, and glucose-insulin homeostasis promoting childhood obesity development.

After this first period, the gut microbial composition continues to evolve until the age of 2-3 years; these first years represent as "a window of opportunity" for microbial modulation, influenced by complementary feeding period, gradual transition from milk-based infant feeding to weaning and solid foods, usually occurring between 6 and 24 months.

A.MA.MI is a longitudinal, prospective, observational study that includes a group of mother-infant pairs (n=60) attending the Neonatal Unit, Fondazione IRCCS Policlinico San Matteo, Pavia (Italy). The study was planned to provide data collected before discharge (T0) and at 1,6,12 months after birth (T1,T2,T3). Maternal and infant anthropometric measurements are assessed at each time. Other variables evaluated are pre-pregnancy/gestational weight status (T0), maternal dietary habits/physical activity (T1-T3); infant medical history, type of feeding, antibiotics/probiotics/supplements use, environment exposures (e.g cigarette smoking, pets, environmental temperature) (T1-T3). A child stool sample was planned to be collected at each time and analyzed using metagenomics 16S ribosomal RNA gene sequence-based methods. Maternal urine samples were planned to be collected at T3 to investigate pollutants exposure (Phthalates, Bisphenol A and Hydroxypyrene).

Since there are still limited knowledge about the child's microbiota, its changes over time and the host and environmental interactions in shaping its composition, further prospective studies are needed to determine how different factors related to diet-related factors, lifestyle, drugs and anthropometric measures can influence microbial colonization of the gut during early childhood and influence the future health status.