Zhang et al. (2021) examined associations between in utero metal and trace element exposures — measured in maternal red blood cells (RBCs) during late pregnancy — and childhood blood pressure trajectories in 1,194 mother-child pairs from the Boston Birth Cohort. The primary finding is a protective effect of selenium and manganese: higher maternal Se and Mn were associated with meaningfully lower childhood systolic blood pressure percentiles, while Pb, Hg, and Cd showed no statistically significant associations with blood pressure in this predominantly low-income, minority urban cohort. The inverse relationships for Se and Mn persisted after adjustment for multiple comparisons and were robust to sensitivity analyses.
Key numbers
| Metal/Element | Maternal RBC mean | Unit | Association with child SBP |
|---|---|---|---|
| Pb | 3.29 | µg/dL | Not significant |
| Hg | 3.15 | µg/L | Not significant |
| Cd | 0.86 | µg/L | Not significant |
| Se | 289.50 | µg/L | −6.23 percentile points per doubling (95% CI: −11.51, −0.96) |
| Mn | 39.57 | µg/L | −2.62 percentile points per doubling (95% CI: −5.20, −0.04) |
Children’s systolic blood pressure was modeled as age- and sex-specific percentiles from the 2017 AAP guidelines. Mean follow-up from delivery to first BP measurement was approximately 4.5 years (range 3-14 years); children contributed a median of 2 BP measurements (range 1-5). Childhood mean SBP was ~110 mmHg; DBP ~62 mmHg. Exposure quartile analyses for Pb, Hg, and Cd showed no dose-response trends. The Se association was strongest among children followed beyond age 6. No interaction by sex or race/ethnicity reached significance.
Methods (brief)
Maternal RBC metals were measured at enrollment (predominantly 3rd trimester) by ICP-MS at the NIEHS laboratory. Speciation is not reported; Hg is reported as total Hg. Blood pressure was measured at clinic visits using standard pediatric protocol (Dinamap Pro). Analyses used linear mixed-effects models with age-SBP trajectories as outcomes; multiple testing controlled via Holm correction. Covariates included maternal age, education, race/ethnicity, smoking, BMI, gestational age, parity, and child sex.
Implications
Certification: Selenium and manganese protective effects on childhood BP do not directly affect HMT&C threshold setting, which focuses on toxic metal upper limits. However, the null result for in-utero Pb (mean 3.29 µg/dL) on childhood BP does not exonerate Pb; the Boston Birth Cohort has lower Pb exposures than many international populations and BP may not be the most sensitive endpoint. Certifiers should not interpret this null as evidence that Pb at these levels is safe for developing cardiovascular systems.
Courses: Relevant for modules on essential vs. toxic metal co-exposures in pregnancy. Demonstrates that protective micronutrient status (Se, Mn) can modify outcomes independently of toxic metal levels — an important teaching point for prenatal nutrition guidance in populations near the environmental-justice margin.
App: Not directly applicable to food contamination profiling (exposure measured as maternal RBC, not dietary). Provides supporting context for maternal Se and Mn dietary targets.
Microbiome: Not directly addressed in this paper.