Prenatal Exposure to Particulate Air Pollution Linked to Sleep Disruption in Early Childhood

CLEVELAND – Babies exposed to particulate air pollution while in the womb are at increased risk of having altered sleep patterns as toddlers – a condition that may have lifelong, irreversible effects on their overall health. That’s the principal finding of new research co-authored by Kristie R. Ross, MD, Division Chief of Pediatric Pulmonology at University Hospitals Rainbow Babies & Children’s Hospital and Associate Professor at Case Western Reserve University School of Medicine. The study was published online in January 2019 in the journal Environment International.

”This is an area that is not well understood and appreciated even by health care providers,” said Dr. Ross. “Particulate air pollution exposure can disrupt fetal brain development, but associations between fine particulate matter exposure during pregnancy and child sleep outcomes have not been previously explored.”

The connections in the brain required for the development of sleep are formed in utero, as early as seven weeks into pregnancy. REM and non-REM sleep also are established prenatally, as early as 28 weeks. Research shows that interrupting these processes can result in reduced sleep duration, more time spent in bed not asleep (reduced sleep efficiency) and circadian rhythm abnormalities once the child is born.

Dr. Ross’ new research shows that prenatal exposure to particulate air pollution is just such an interruption.

“Sleep is an active process controlled by the brain,” she said. “It is vulnerable to disruption from a number of different things, and toxin exposure is one of those things.”

Previous research has shown that exposure to particulate air pollution affects fetal brain structure, function and development, with some linkages to cognitive and behavioral disorders in children. In addition, prenatal exposure to particulate matter in the air has been shown to alter neurotransmitters across several brain regions and cause changes in the child’s circadian pathway genes, specifically during the third trimester of pregnancy.

However, until now, there have been no published studies examining the impact of prenatal exposure to particulate air pollution on sleep patterns in early childhood.

According to Dr. Ross, evidence suggests that babies are most vulnerable to these effects during specific periods during pregnancy.

“This suggests that associations between prenatal toxic exposures and postnatal sleep disorders may depend on timing of exposure as well as dose,” she said.

For their study, Dr. Ross and colleagues from the United States and Mexico analyzed 397 mother-infant pairs in Mexico City and gauged their exposure to particulate air pollution.

Children in the study then wore a wrist actigraphy monitor at age 4 or 5, which the researchers used to estimate their sleep patterns and quality. The researchers also used an advanced statistical model to identify those windows when exposure to particulate air pollution during pregnancy was associated with changes in sleep duration or efficiency.

Results show that babies exposed to particulate air pollution in utero did indeed have altered sleep as toddlers, after adjusting for other factors. Children in the study slept on average 7.8 hours over a 24-hour period – far below the 10 to 13 hours of sleep recommended for children of this age. The exposure window between 31 and 35 weeks of pregnancy was significantly linked to decreased sleep duration. In addition, the window between one and eight weeks gestation – before many women even know they’re pregnant – was linked to decreased sleep efficiency in the children -- more time spent in bed not asleep.

“The relationships we report show there are critical periods during pregnancy during which exposure can disrupt sleep programming with lasting results,” Dr. Ross said.

“Sleep is an often-overlooked but absolutely necessary biologic function that plays a tremendous role in our health,” she said. “For children in particular, disrupted sleep leads to difficulties with focus, concentration, controlling emotions, and learning. There are also relationships between sleep disruption and the development of obesity and metabolic disorders like diabetes and hypertension. There’s some literature suggesting that later in life, sleep disruption may be associated with increased risk for heart attack and even cancers.  Healthy sleep is important for almost every aspect of well-being.”

“The concern is that if we’re disrupting the brain’s ability to develop normal sleep patterns, that can have lifelong impacts,” Dr. Ross said. “There’s the concern that this could be irreversible. Children are remarkably resilient and we’ve able to intervene and make things better in a lot of cases. But not everything gets better. They don’t reach the same potential on neurocognitive outcomes that they would if they were not affected by disrupted sleep.”

For Dr. Ross, this study is new and compelling evidence for the importance of maintaining clean air and protecting children’s growing and developing brains.  She is continuing to collaborate with other researchers to better understand the relationship between air pollution and other toxic stress exposure during pregnancy and healthy sleep in another group of children born in the U.S. 

“Add this to the long list of ways air quality and climate change are important public health issues,” she said.

Other institutions involved with the study: Icahn School of Medicine at Mount Sinai, New York; Ben-Gurion University of the Negev, BeerSheba, Israel; Colorado State University; Harvard Medical School and Harvard Pilgrim Health Care Institute; Instituto Nacional de Salud Pública Cuernavaca, Morelos, Mexico, and National Institute of Perinatology “Isidro Espinosa de los Reyes,” Mexico City, Mexico.