Let Them Eat Dirt. B. Brett Finlay

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СКАЧАТЬ measure to maintain a balanced microbiota during pregnancy is to avoid stress, which is always easier said than done. We’ve all felt it—stress is a condition that affects most people at some point or another. It can be helpful sometimes, like when it compels you to finish an assignment for work that’s due the next day. The problems arise when stress becomes an everyday companion; this is when it affects our health. Stress can make you lose sleep, have headaches or stomachaches, overeat, or lose your appetite. While pregnancy is typically a very joyful time, it can also be difficult. Dealing with the physical discomforts such as nausea, exhaustion, and backaches may quickly add up. On top of that, hormonal changes affect mood and the ability to handle stress.

      A moderate level of stress is unlikely to cause a major impact on the health of a mother or her baby. However, certain situations may lead to severe stress, which can have detrimental effects on the pregnancy and the health of the baby. Abrupt negative life events, such as divorce, serious illness, financial problems, partner abuse, depression, and the conflicting feelings surrounding an unplanned pregnancy—to name a handful—are all causes of long-lasting or severe forms of stress. Some women suffer severe stress and anxiety when faced with the idea of labor or parenting. Severe stress is associated with preterm and low-weight births, and with certain illnesses in children, including skin conditions, allergies, asthma, anxiety, and even attention-deficit hyperactivity disorder (ADHD; see chapter 14).

      A recent study from the Behavioural Science Institute of Radboud University, in the Netherlands, suggests that the microbiota plays a leading role in the link between stress during pregnancy and the aforementioned disorders. This study, which recruited fifty-six pregnant mothers, found that women who experienced high and prolonged levels of stress had alterations in the vaginal microbiota that could also be detected in their babies’ gut microbiota. Infants born to highly stressed mothers showed lower levels of beneficial microbes, such as lactic acid bacteria. In the same study, these changes to the microbiota were associated with more gastrointestinal issues and allergic reactions in babies. They also found that the negative effects of severe maternal stress could not be corrected by breastfeeding, even though it has been repeatedly shown to promote a healthy microbiome in infants.

      A similar study aimed at exploring the link between maternal stress and the microbiota was recently performed in mice. The study showed that a reduction in vaginal lactic acid bacteria, caused by stress, is accompanied by decreased immune functions in the offspring. Furthermore, the changes in the baby mice were not limited to the types of bacteria growing in their guts; there were also important metabolic differences detected in their blood and their developing brains. It may well be that the vaginal microbiota is at the center of this, responding to maternal stress and transferring its imbalanced state to the newborn, where it can lead to lasting health consequences. Although a casual relationship remains to be established, it appears that lactic acid bacteria from vaginal secretions are not only involved in facilitating milk digestion in newborns, but also carry out important metabolic functions in the developing newborn—yet another reason to reduce stress as much as possible and to take daily probiotics during pregnancy.

Infections and Antibiotics: Can We Avoid Them?

      Controlling your diet and your stress levels during pregnancy is an enormously challenging goal for most women, but it can be done. However, the microbiota of pregnant women can suffer a big blow through a situation that’s out of their control: taking antibiotics to treat an infection. As mentioned before, pregnant women are more vulnerable to infections, and if they occur, they are likely to be more severe due to their compromised immune systems. This is why it’s recommended that pregnant women wash their hands often, avoid caring for people with infections (good luck with that when you have other kids!), avoid gardening without gloves, cook meats thoroughly, avoid changing the cat litter box, and avoid deli meats, sushi, and unpasteurized milk. Pregnancy is definitely not the time to get dirty and eat dirt, as we will later suggest our kids should do (although some pregnant women have an urge to do so—see Care for a Spoonful of Soil? on page 51).

      Despite best efforts to avoid them, infections during pregnancy are quite common, with urinary tract infections (UTIs) and bacterial vaginoses both affecting about 1 in 6 pregnant women in the United States and about 1 in 10 pregnant women in Canada. Other commonly diagnosed infections during pregnancy are respiratory tract and skin infections. Fortunately, several antibiotic medications are safe to use during pregnancy, but they’re being prescribed to a lot of women—very likely more than necessary. The most recent National Birth Defects Prevention Study in the US, which has been collecting data since 1997, showed that almost 30 percent of women receive at least one course of antibiotics during pregnancy. A population-based study (a term given to studies involving a very large number of people) in the UK showed that the same is true for British women, while 42 percent of French and 27 percent of German women take antibiotics while pregnant. There’s no debate about the immense change that an antibiotic brings to the microbiota. After a course of antibiotics, the overall diversity of the microbiota is substantially reduced. Its effect can be compared to what happens when a lush rain forest gets chopped down, and only a few dominant species make a comeback. Fortunately, the adult microbiota is fairly stable, and after finishing a course of antibiotics, in a nonpregnant woman this microbial forest usually returns to normal. The concern during pregnancy is that the microbiota fluctuates considerably, which is a characteristic of unstable ecosystems that are more susceptible to abrupt changes and permanent damage. When expectant women take antibiotics, especially in the last two trimesters, their microbiota takes a major hit, and according to new research, so does the microbiota of their babies. What becomes even more concerning is that antibiotic use during pregnancy is now being associated with certain diseases seen later in children.

      A study of more than seven hundred pregnant women from New York showed that children born to those who received antibiotics in their second and third trimesters had an 85 percent higher risk of childhood obesity by age seven. These results are very significant because they were obtained after correcting for other confounding variables of obesity, such as the weight of the mother, the birth weight of the child, and whether or not the infant was breastfed. All of these factors were previously shown to be associated with the risk of obesity, so it’s important (for this and any other similar study) to remove these variables from the analysis. These findings are quite new (published in 2014) and they still need to be replicated, but if more studies show a similar trend, it suggests that childhood obesity may have roots in the very early stages of human development, and that antibiotic use during pregnancy has significantly more risk than is currently assumed in medical practice.

      Antibiotic use during pregnancy has also been associated with asthma, eczema, and hay fever in infants. Two large studies from Finland, a country that has experienced a twelve-fold increase in asthma rates since the 1960s, showed that using antibiotics during pregnancy is a significant risk factor for early asthma in babies. Other epidemiological studies have found similar associations between antibiotic use during pregnancy and inflammatory bowel disease (IBD) and/or diabetes, each of which is discussed in detail in forthcoming chapters. What’s very peculiar is that these diseases share common risk factors. They are all immune disorders that have become increasingly common in the past few decades, and they usually occur in individuals with certain known genetic predispositions. Recent research on humans and animals show that the risk factors associated with these diseases also involve the early microbiota. How early? According to the studies, these changes begin before we’re born, through mechanisms that are just beginning to be understood.

      As frequently occurs in science, the insights on the mechanisms that explain a disease come from animal experiments. In this case, neonatology researchers from the Children’s Hospital of Philadelphia showed that baby mice born to mothers that received antibiotics during pregnancy had a reduced immunological response. Similarly, a separate study showed that mice predisposed to diabetes and born to females that were given antibiotics had persistent alterations in their immune cells. These same mice developed diabetes a lot sooner than mice born to females that did not receive antibiotics. СКАЧАТЬ