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A number of studies have linked stress during pregnancy to premature birth and low birth weight, eczema, asthma, skin condition, and general illness as well as anxiety, attention-deficit hyperactivity disorder (ADHD) and impaired cognitive and psychomotor development.1 The reasons for these associations is not completely understood. Some researchers believe that gut microbes play a role.

Intestinal microbes affect the development of an infant’s immune system, development of the gastrointestinal tract, and hormone function. Infants receive their gut microbes largely from their mother—especially if they are delivered vaginally and breastfed—and to a smaller extent from their environment. Compromised development of a healthy balance of gut bacteria during infancy can have long-lasting negative health effects.

In a recent study published in the journal Psychoneuroendocrinology, researchers found that women who experience stress during pregnancy are more likely to have babies with an imbalance of gut bacteria and worse gastrointestinal problems and allergic reactions when compared to women with less prenatal stress.1

Fifty-one mother-infant pairs were involved in the study. Stress levels during pregnancy along with salivary cortisol levels were measured. Cortisol, known as the stress hormone, is secreted under conditions of stress and so is a biological marker of stress. Those women with either high stress levels as measured by questionnaires or high cortisol levels were more likely to deliver babies with greater gut bacterial imbalance.

Fecal samples were collected up to five times beginning at seven days after birth up to four months after birth. Mothers with high stress and high cortisol levels had babies with higher amounts of Proteobacteria, which is comprised of a number of pathogenic species, and lower amounts of lactic acid bacteria (a group including the beneficial Lactobacillus) and Actinobacteria (a group including the beneficial Bifidobacterium). These children also experienced greater gastrointestinal symptoms and allergic reactions. Even breastfeeding, which is known to help promote the growth of beneficial bacteria in the gut due to its prebiotic content, was not enough to protect from the negative effects of stress.

“We think that our results point towards a possible mechanism for health problems in children of mothers who experience stress during pregnancy,” noted Carolina de Weerth, lead researcher. “Giving other bacteria would probably benefit these children’s development.”

The researchers suggest that cortisol may be affecting gut microbes in three main ways. First, cortisol may be interfering with bile production which can have an effect on gut bacteria. Second, cortisol may cross the placenta and increase fetal cortisol levels, which might affect the development of the gastrointestinal tract and impact gut bacteria. Third, cortisol may be transferred to the infant from breast milk. Cortisol is not the only mechanism, however, since prenatally stressed women without elevated cortisol also had babies with gut imbalance. The researchers suggest that the effects of stress on the endocrine and immune systems might be to blame. These mechanisms require further study.

Indeed, this study points to the need for a diet high in plant-based foods that feed the beneficial bacteria in the gut, supplementation with pre- and probiotics, and stress-reduction therapies such as meditation during pregnancy. Lactobacillus and Bifidobacterium bacteria are sensitive to environmental disturbances, and yet are well known to be crucial to the development of a healthy gut microbiota in children. Replenishing this population of bacteria—and preventing its depletion—during pregnancy, infancy, and beyond is crucial.

References

  1. Zijlmans MAC, Korpela K, Riksen-Walraven JM, et al., “Maternal Prenatal Stress and Infant Intestinal Microbiota.” Psyconeuroendocrinol. 2015;19 Jan: online ahead of print.