Fetal micro-organisms can provide critical window into person's future
Science relatively young, but exciting discoveries made, writes Peter Nieman
In the development of health and disease, there are key moments where future trajectories are established. This early programming sets the stage for long-term health and also the prevention of future diseases.
These so-called critical windows were originally known as the Barker Hypothesis. In 1990, British epidemiologist David Barker proposed an association between fetal malnutrition and hypertension later in life. Other examples are breast and colon cancer. High birth weights are associated with an increase of these cancers partially due to intrauterine exposure to high levels of growth hormones.
During the past decade, the microbiome has emerged as a major contributor to human health. The organisms found in the gut matter a great deal more than we ever realized in how they impact the rest of the body.
This emerging science is relatively young, but exciting discoveries continue to be made. I use the analogy of ancient explorers who sailed west from Europe, not knowing what they were about to discover. Bit by bit they found out about new continents. Similarly, scientists continue to discover the importance of critical windows.
The human microbiota is composed of 10 to 100 trillion microbial cells and viruses. These organisms play a huge role even before birth. (Initially, it was thought that the intrauterine environment was sterile. However, non-pathogenic bacteria have since been detected by molecular techniques in the amniotic fluid and the placenta of healthy infants)
The gut microbiome of the fetus is influenced by various factors such as the mother’s diet, gestational diabetes, the mother’s blood pressure, the birth weight, preterm birth, the administration of antibiotics to the mother — both prenatally and postnatally — and the method of delivery. These factors may partially determine if a baby will go on and develop allergies, obesity, inflammatory illnesses and neurodevelopmental illnesses.
Premature babies are at risk for developing necrotizing enterocolitis (NEC), a condition where the bowels are severely damaged to the point of not allowing any nutrition via the mouth. Antibiotics are used to treat NEC. These medications then disturb the gut microbiome further. The idea of using probiotic supplementation to help restore the microbiome to a more ideal environment did not exist until recently.
Many doctors are also more aware of the role caesarean sections play. Babies born by caesarean section are deprived of the opportunity to pass through the mother’s birth canal, where they get colonized by good bacteria provided by the mother. This may impact their risk for allergies later in life. Research is underway to determine if recolonizing infants delivered by caesarean sections within two minutes of birth may be able to partially restore the microbiota, thus reducing the risk for illnesses later in life.
When medical students were taught about the benefits of breastfeeding in the past, their teachers never mentioned how breastfeeding impacts the human gut microbiome. Now we know that breastfeeding greatly benefits it. The good bacteria are derived not only from the breast milk, but also from the skin of the mother’s areolar area.
The role of neonatal stress has been studied in animals. When rat pups were separated from the mother, the composition of the gut microbiota changed. Treating the rat pups with probiotics countered the resulting elevated cortisol caused by stress. Much more research is needed before we can demonstrate the same effect in humans, but the role of stress and how it impacts gut health (microbiome) will no doubt be a factor.
The causes of common conditions such as allergies, asthma, eczema, obesity, inflammatory bowel disease, depression, autism and attention deficits are complex and multi-layered. Being more aware of the critical times of establishing a healthy microbiome may help reduce the risk of these conditions.
Practically, it means that we need to pay even more attention to what mothers eat while pregnant. Caesarean sections must be done for the right reasons; maternal antibiotics and antibiotics to newborns can save lives, but the role of probiotics after the use of antibiotics must not be forgotten or ignored; breastfeeding for as long as possible assists the maturation of the gut microbiome; and the use of antibiotics early in life should be carefully considered and used only appropriately.
From an ethical standpoint, I find this science both disturbing and exciting. Disturbing in that some humans may now be paying the price later in life because doctors were not aware of the importance of protecting the gut microbiome more aggressively and some mothers may have guilt that they did not eat better during pregnancy. But it is also exciting to know that we can reduce the risk of future problems by paying closer attention to the gut microbiome — especially during these critical window moments.