A Canadian birth cohort analysis examines how an everyday beverage may shape prenatal fluoride exposure and why clearer product labeling could matter.
Study: Prenatal fluoride exposure and child IQ: Is tea a key source of fluoride? Image Credit: Kittyfly / Shutterstock
In a recent study published online as a Journal Pre-proof in the journal Environmental Pollution, researchers evaluated associations between estimated prenatal fluoride exposure from maternal tea intake during pregnancy and child intelligence.
A growing body of evidence indicates that systemic fluoride exposure, especially during pregnancy and early childhood, may have developmental neurotoxic effects. Among people living in fluoridated communities, tap water is the primary source of exposure. Some teas, particularly brick and black teas, can contain relatively high concentrations of fluoride because the tea plant is a bioaccumulator. Fluoride levels vary by tea type, with the highest reported in fully fermented teas, and are influenced by brewing duration.
Tea consumption can account for up to 48% of total fluoride exposure in adults. Prospective birth cohort studies have reported inconsistent associations between children’s intelligence quotient (IQ) and prenatal fluoride exposure, which may reflect differences in exposure levels, exposure measures, and approaches to controlling for confounding factors.
About the study
In the present study, researchers investigated associations between prenatal fluoride exposure from maternal tea consumption during pregnancy and children’s IQ. Participants were mother-child pairs from the Canadian Maternal-Infant Research on Environmental Chemicals cohort. Maternal beverage consumption was assessed using questionnaires administered in the first and third trimesters and used to estimate fluoride intake.
The team used average fluoride levels reported in a previous review for green tea and black tea to estimate fluoride intake from these beverages. The estimates also incorporated fluoride in the tap water used to prepare each 200 mL cup. In addition, total fluoride intake from all water-based beverages, including herbal tea, black tea, coffee, green tea, and tap water, was estimated. Spot urine samples collected during each trimester were used to measure maternal urinary fluoride concentrations, which were adjusted for specific gravity and averaged across pregnancy. These measurements were compared with the estimated intake variables rather than used as the primary exposure measure in the IQ models.
The Wechsler Preschool and Primary Scale of Intelligence (WPPSI)-III was used to assess children’s intellectual abilities. Full-scale IQ (FSIQ), performance IQ (PIQ), and verbal IQ (VIQ) scores were derived. FSIQ was the primary outcome, whereas PIQ and VIQ were secondary outcomes. Correlations between urinary fluoride levels and fluoride intake variables were evaluated.
Associations between estimated fluoride intake from tea and children’s IQ were estimated using multiple linear regression models, adjusted for child sex, maternal education, race/ethnicity, and study site. The team tested effect modification by pre-pregnancy body mass index (BMI), child sex, Home Observation for Measurement of the Environment (HOME) score, race/ethnicity, and maternal education.
A secondary model assessed the association between total fluoride intake and children’s IQ, including an interaction term to examine whether it differed between tea non-consumers and tea consumers. In sensitivity analyses, the primary model was adjusted for additional covariates, including HOME score, caffeine intake, pre-pregnancy BMI, alcohol intake, and secondhand smoke exposure. The primary model was also re-estimated using lower estimates of fluoride levels in tea.
Findings
The primary analysis included 485 mother-child pairs, whereas the analysis of total fluoride intake included 464 pairs because 21 participants lacked water-consumption data. Most mothers had a university education (68%) and identified as White (88%). The child cohort had a balanced sex distribution, with an average age of 3.4 years at cognitive assessment. The average FSIQ score was 107.1, indicative of average performance. Among 428 women with available measurements, the mean maternal urinary fluoride level was 0.55 mg/L.
Urinary fluoride levels showed weak correlations with estimated fluoride intake from tea and moderate correlations with fluoride intake from all beverages. About 23% of mothers reported consuming coffee daily during pregnancy. Further, 2.3% and 8.4% of mothers consumed green tea and black tea, respectively, at least daily. Overall, 61% reported consuming some black tea, green tea, or both during pregnancy.
There was a significant inverse association between estimated fluoride intake from tea and FSIQ scores. Specifically, each 0.5 mg/day increment in estimated fluoride intake from tea, approximately equivalent to the estimated fluoride content of one standard cup of black tea, was associated with a 2.24-point lower FSIQ score (p = 0.009).
Estimated fluoride intake from tea was also inversely associated with VIQ but was not significantly associated with PIQ. Each 0.5 mg/day increment in total fluoride intake was associated with a 1.67-point lower FSIQ score (p = 0.022).
The interaction term with tea intake status was not significant, providing no statistical evidence that the association between total fluoride intake and FSIQ differed between tea non-consumers and tea consumers. The significant associations remained when additional covariates were included in the sensitivity analysis, although the sample size was reduced due to missing covariate data.
Using lower estimates of fluoride levels in tea to recalculate exposure yielded a larger regression estimate: a 0.5 mg/day increment in estimated fluoride intake from tea was associated with a 3.3-point lower FSIQ score. However, the observational study cannot establish causality. Beverage intake was self-reported, fluoride concentrations in participants’ actual tea were not measured, parental IQ was unavailable, and other dietary fluoride sources were not assessed. The predominantly White, highly educated cohort and restriction to public tap-water consumers also limit generalizability.
Conclusions
In summary, higher estimated fluoride exposure from maternal tea intake during pregnancy was inversely associated with child FSIQ scores at 3 to 4 years of age. These results underscore the need to monitor fluoride levels in tea and increase transparency about their levels in tea products.
The authors suggested that pregnant individuals may consider limiting tea consumption because it can be a major source of fluoride. However, only one tea consumer exceeded the cited fluoride intake level of 3.3 mg/day, and the study did not establish a safe or harmful number of cups. The study also did not assess whether reducing tea consumption would improve children’s cognitive outcomes. Further studies are needed to replicate these findings across demographic contexts.
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