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Maternal Mercury Ups Risk for Childhood Obesity
— Association seems to be mitigated by folate intake
by Elizabeth Hlavinka, Staff Writer, MedPage Today April 30, 2019
BALTIMORE -- Pregnant women with elevated mercury levels were at a higher risk of having children who were overweight or obese, researchers said here.
The increased risk was concentrated mostly in women with mercury levels in the fourth quartile (3.7-27.8 ug/L), who were significantly more likely to have children who went on to become overweight or obese (BMI ≥85 percentile) compared with women with lower levels (odds ratio 1.37, 95% CI 1.06-1.76, P=0.02), reported Tina Cheng, MD, of Johns Hopkins University here, and colleagues.
Maternal folate use seemed to moderate this association, with mothers in the fourth quartile demonstrating a 61% decrease in mercury levels when receiving adequate folate levels versus low folate (P=0.065), the researchers said at the Pediatric Academic Societies meeting.
The results were adjusted for maternal age, race, smoking, education, parity, hypertensive disorder, preterm birth, fetal growth, and breastfeeding.
"Mercury is of particular concern because of its ability to cross the blood-brain barrier and placenta with fetal susceptibility and bio-accumulation," Cheng said. "The question was whether the in-utero exposure to mercury increased the risk of overweight or obese [children] later in life."
Folate has been shown to mitigate the risk of intergenerational obesity and elevated blood pressure, she explained. And although pregnant women are advised to take at least 600 micrograms daily to prevent neural tube defects, folate's efficacy in counteracting the toxicity of mercury is unclear, she added.
Overall, the fact that folate intake during pregnancy seemed to improve the risk of childhood obesity "provides a really strong causal inference," that mercury levels are indeed tied to childhood weight status, said William Heerman, MD, MPH, of Vanderbilt University in Nashville, who was not involved with the study.
"We know early-life risk factors have long-lasting effects on many child health outcomes, including childhood obesity," Heerman told MedPage Today. "But what was most interesting to me was that folate mitigated that risk -- if you have a high level of mercury in the mother you had a higher rate of obesity later, but if you had adequate folate, that risk was lower."
However, Heerman emphasized that unmeasured confounders could potentially be driving this association as well -- particularly other measures of socioeconomic status that are tied to a risk for higher levels of mercury.
For this study, researchers enrolled mother-child pairs in the Boston Birth Cohort, which is comprised of an urban, low-income minority population. The team collected blood samples from mothers from 2 to 3 days after birth to represent third trimester mercury exposure, evaluated through both red blood cell mercury concentrations and plasma folate. The children were followed up from birth to 15 years.
In total, 1,442 children were included; about two-thirds of the total were black, and half were boys. Just over half of the mothers involved in the study were overweight or obese and 13% had diabetes. About 40% of the children were overweight or obese.
Overall, 13.5% of women in the study had mercury levels above 5.8 ug/L, which is the Environmental Protection Agency's reference level, with a median amount of 2.11 ug/L. Meanwhile, 21.4% of the women were found to be receiving insufficient folate (20.4 nmol/L), with a median level of 32.3 nmol/L across the group, Cheng said.
The association between maternal mercury exposure and childhood overweight or obesity status persisted across preschool children (ages 2-5), school age (6-9), and adolescence (10-15), with mothers in the fourth percentile for mercury exposure being significantly more likely to have children who were overweight or obese in each group, the researchers reported.
Lastly, mothers who were overweight or obese in the top quartile were at three times the risk of having children who were also obese or overweight, whereas mothers in the top quartile with diabetes had twice the risk as mothers in lower quartiles, suggesting these two conditions "might increase the adverse effects of mercury," Cheng said.
She noted that the study is limited because the team measured the total levels of maternal mercury but did not account for methyl mercury, the major source of organic mercury, and also did not collect data on childhood mercury levels after birth. Lastly, she said, the mother-child pairs evaluated in this study were mostly in minority groups from low socioeconomic backgrounds, and these results may not be generalizable to other populations.
Elizabeth Hlavinka covers clinical news, features, and investigative pieces for MedPage Today. She also produces episodes for the Anamnesis podcast. Follow
The cohort in this study was supported by grants from the National Institutes for Health and the Health Resources and Services Administration.
Cheng did not report any relevant disclosures.
Pediatric Academic Societies
Source Reference: Cheng T, et al "Maternal mercury levels and folate status with child's overweight or obesity up to age 15 years" PAS 2019; Publication number 3690.1.