Fetuses of women who live in smoggy cities have altered thyroid development, raising concerns about health impacts later in life, according to USC research findings announced Monday.
It’s one of a few studies to monitor air pollution effects on a developing fetus and the first to track pollution changes month by month on thyroid hormones, according to the university.
“Air pollution is bad for adults and children and this study shows it may be bad for the fetus too, despite being protected in the womb,” said Carrie V. Breton, corresponding author of the study and associate professor of preventive medicine at the Keck School of Medicine of USC. “Thyroid function is important for lots of elements of life and tweaking that in utero may have lifelong consequences.”
USC scientists have been studying the health impacts of urban air pollution since 1992 under the Children’s Health Study, which is touted as one of the world’s largest ongoing research efforts looking exclusively at how dirty air harms kids. USC is located in the Los Angeles region, which has historically suffered from severe smog.
In the new study, which is outlined in the JAMA Network Open medical journal, the research team focused on 2,050 people who had been enrolled in the Children’s Health Study previously, selected using birth data from the mid-1990s, when they were students at 13 Southern California schools. About 60 percent were white, 30 percent Latino, and the remainder black or other races. The participants were included only if they had blood tests taken right after birth and had complete monthly exposure measures for air pollution throughout pregnancy.
The study monitored blood levels for total thyroxine (TT4), a hormone secreted by the thyroid gland, and found that when exposure to PM2.5 — a sooty particle 20 times smaller than the diameter of a human hair — increased by 16 micrograms per cubic meter of air, TT4 levels in blood increased 7.5 percent above average levels in babies. When exposure to PM10 — an airborne particle which often comes from dirt dust and pulverized road grit — increased by 22 micrograms per cubic meter, TT4 levels increased by 9.3 percent, according to the study.
The researchers did not find the same increases associated with other air pollutants, such as ozone or nitrogen dioxide. They also found exposures during months three to seven of pregnancy were most significant for PM2.5, and PM10 exposure during one to eight months of pregnancy was associated with significantly higher newborn TT4 concentrations.
The study found that the fetal thyroid gland seems particularly susceptible to airborne particulates, especially during early- to mid-pregnancy, which is consistent with previous studies by other researchers.
The study did not assess the health effects of the air pollution exposures, and only looked at one hormonal pathway associated with the thyroid gland, which the authors acknowledged is a limitation. But the authors did note that even subtle changes in maternal thyroid function during pregnancy have been associated with reduced fetal growth and cognitive deficits in children.
“There are several places around the world where air pollution is skyrocketing,” Breton said. “This is another example of an environmental exposure that affects early development in subtle ways, and we don’t know the health consequences.”
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