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Prenatal smoking reduces infants’ stress-coping ability, study finds

Low levels of stress hormone can lead to inadequate external response, development

Smoking during pregnancy can render newborn babies less able to produce a physiological response necessary to cope with daily stressors, according to a new study by Brown researchers.

The research team, made up of psychiatrists and behavioral scientists from Alpert Medical School and Miriam Hospital, compared 53 newborns whose mothers had smoked during pregnancy and 47 who had not, according to the study. They found that newborns of mothers who had smoked exhibited decreased stress responses compared to control subjects with non-smoking mothers.

The study was published in the current edition of the journal Psychoneuroendocrinology.

The team measured the babies’ stress responses by sampling their levels of cortisol, a hormone that is released in response to stress, said Laura Stroud, lead author of the paper and associate professor of psychiatry and human behavior. The stress response is first modulated in the brain’s hypothalamus, which releases signals that travel through the rest of the body, Stroud said.

In the study, the researchers administered a neurobehavioral exam to the babies, which was intended to raise the babies’ cortisol levels, according to the paper. They found that babies of mothers who had smoked during their pregnancies showed weaker spikes in cortisol levels.

Though a lower stress response may sound like a beneficial mutation, it can actually be detrimental to a baby’s development, Stroud said. Humans need to be able to raise their stress levels daily in order to adequately respond to external stressors, she added.

The process by which changes occur in fetuses exposed to toxins is still somewhat unclear, but this study’s use of a repeated behavioral assessment is a step in the right direction, said Kimberly Yolton, an associate professor of pediatrics at the University of Cincinnati, adding that the methods were “innovative.”

“The study adds another layer of evidence to the huge pile of evidence that we already have that a mother’s smoking is bad for the fetus,” Yolton added.

A proper stress response system is especially important for children of mothers who smoke during pregnancy because these women are more likely to be younger, less educated and have less developed parenting skills, Stroud said.

“A combination of a baby who can’t cope with stress combined with a mom who might be causing stress is not a good one,” she said.

Many of the health problems caused by smoking during pregnancy are best treated though social and not medicinal interventions, Stroud said, adding that this line of biological research can improve health outcomes if used to change policies. For example, mothers could be provided with additional educational opportunities to learn about the effects of smoking on their babies.

The neurobehavioral exam used in the study was sometimes administered in the subjects’ homes, according to the paper. Though the study stated that the researchers conducting the neurobehavioral exam did not know whether the mothers smoked or not, Yolton said that it would be easy to tell if the mother smoked by the smell of the home, which may have influenced the study’s results.

The researchers plan to move forward with several new research projects to elucidate the mechanism and causes of the altered stress response, Stroud said.

One study will focus on the role  DNA methylation, since previous work suggests that methylation may silence genes that normally play a role in the response.

The researchers also plan to conduct a longitudinal study, following babies of smoking and non-smoking mothers for six months after birth to determine the length of time for which differences in their stress responses persist.


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