Manganese Overload in Infants and Toddlers: The U-Shaped Curve You Need to Know About

Manganese is quietly essential. Your child's brain needs it to activate enzymes, protect neurons from oxidative stress, and develop normally. But this same metal, in excess, accumulates in the basal ganglia and disrupts the very circuits that govern attention, impulse control, and movement — producing a picture that looks strikingly like ADHD. The dose makes the poison, and with manganese, the margin between "enough" and "too much" is narrower than most parents realize. Two everyday exposures — soy-based infant formula and well water — can push children past that margin without any obvious warning signs.

Why the Dose-Response Curve Is U-Shaped

Both deficiency and excess cause harm. Manganese is a required cofactor for enzymes including arginase and superoxide dismutase, and it is genuinely necessary for brain development (Lucchini et al., Advances in Neurobiology, 2017). True deficiency is exceedingly rare in children who eat varied diets (Parmalee et al., Neurotoxicology, 2016). The practical danger for most families sits at the other end of the curve.

When intake is excessive, manganese accumulates in the brain — particularly in the basal ganglia — and produces neurotoxic effects (Bjørklund et al., Environmental Research, 2017). In adults, severe overexposure causes manganism, a Parkinson-like syndrome with tremor, rigidity, and gait disturbance (Parmalee et al., Neurotoxicology, 2016). In children — whose brains are still forming, and whose gut absorbs manganese far more efficiently than adult gut does — the threshold for harm is lower, and the consequences skew toward cognitive and behavioral disruption rather than frank motor disease (Erikson et al., Pharmacology & Therapeutics, 2007).

The Soy Formula Problem

Soy-based infant formula contains substantially more manganese than human breast milk or cow's-milk formula. The concern isn't theoretical. Crinella's expert review examined whether the high manganese content of soy formula could be causally linked to ADHD-like outcomes, concluding that the evidence warranted serious public-policy attention (Crinella et al., Expert Review of Neurotherapeutics, 2012). Infants fed soy formula are exposed during a window — roughly the first year of life — when the basal ganglia and frontal cortex are at their most manganese-vulnerable (Erikson et al., Pharmacology & Therapeutics, 2007).

The frontal cortex connection matters because that is where executive function lives. Higher manganese exposure in early life has been associated with impairments in cognitive and executive function mediated partly through frontal cortical pathways (Lucchini et al., Advances in Neurobiology, 2017). A systematic review and meta-analysis of biomarker studies found that elevated manganese exposure was associated with adverse neurodevelopmental outcomes in children, including cognitive and behavioral effects (Liu et al., Environmental Health, 2020). The evidence doesn't prove soy formula causes ADHD in otherwise healthy children — that causal chain remains incompletely established — but it is sufficient to raise the question loudly.

Well Water: A Hidden Source

Private wells are unregulated for manganese in most jurisdictions, and manganese leaches naturally from soil and rock into groundwater. Children in homes with well water are at measurable risk of elevated exposure (Bjørklund et al., Environmental Research, 2017). One of the most concrete findings in this literature: children who ingested well water manganese at or above 0.241 mg/L for at least three years performed significantly worse on measures of language, mathematics, and overall academic achievement, and scored lower on neurobehavioral test batteries (Bjørklund et al., Environmental Research, 2017).

A systematic review of school-age children specifically exposed through drinking water found consistent associations between manganese exposure and adverse cognitive and behavioral outcomes (Iyare et al., Neurotoxicology, 2019). The IQ-score associations are not trivial: a broader umbrella review of meta-analyses on heavy metal exposure found that manganese was among the metals with the clearest links to cognitive impairment in children (Song et al., Journal of Hazardous Materials, 2025). Practical and cost-effective approaches exist to remove manganese from drinking water — point-of-entry filtration, oxidation followed by filtration — but families on private wells often don't test, because they don't know to (Bjørklund et al., Environmental Research, 2017).

Iron Deficiency Amplifies the Risk

Here's the interaction most pediatricians don't mention: iron deficiency increases manganese absorption. Manganese and iron share transport mechanisms in the gut and brain, and when iron is low, those transporters upregulate, pulling in more manganese (Bjørklund et al., Archives of Toxicology, 2020). Iron deficiency is common in infancy and toddlerhood — and it is also common in children fed soy formula, who may have reduced iron bioavailability from phytates. The combination creates a compounding vulnerability. A child who is iron-deficient and drinking formula high in manganese, or drinking manganese-laden well water, may absorb considerably more manganese than a child with replete iron stores (Bjørklund et al., Archives of Toxicology, 2020).

What the Behavioral Picture Looks Like

Research with exposed children — studied through measures of inattention, hyperactivity, and impulsivity — consistently identifies a behavioral profile that overlaps with ADHD (Menezes-Filho et al., Revista Panamericana de Salud Pública, 2009). A review of recent findings documented that manganese-exposed children showed deficits in cognitive performance, motor function, and behavioral regulation (Zoni et al., Current Opinion in Pediatrics, 2013). Importantly, the effects appear to be dose-dependent and developmentally sensitive: earlier exposure, during peak brain formation, carries greater risk (Erikson et al., Pharmacology & Therapeutics, 2007).

This doesn't mean every child on soy formula or well water will develop attention problems. It means exposure is a modifiable risk factor that deserves the same attention we now give to lead.

Concrete Steps for Parents

If your child drinks well water: Test it. Contact your county health department or a certified lab; ask specifically for manganese alongside lead and nitrates. The U.S. EPA's health advisory for manganese in drinking water is 0.3 mg/L for adults; some researchers argue this is too high for infants. If levels are elevated, point-of-entry filtration or switching to municipal water while the child is young are both reasonable options (Bjørklund et al., Environmental Research, 2017).

If your infant is on soy formula: Discuss with your pediatrician whether cow's-milk formula or continued breastfeeding is medically appropriate. Soy formula has legitimate uses — galactosemia, confirmed cow's-milk protein allergy — but "I heard it was healthier" is not one of them given the current evidence (Crinella et al., Expert Review of Neurotherapeutics, 2012).

Check iron status. A simple ferritin level at the 9- or 12-month well visit can identify children whose iron deficiency may be amplifying manganese uptake. Treating iron deficiency is good practice in any case; in the context of potential manganese exposure, it becomes more urgent (Bjørklund et al., Archives of Toxicology, 2020).

If you're concerned about past exposure: Blood manganese levels can be measured, though they reflect recent rather than cumulative exposure. A developmental pediatrician or pediatric neurologist can help interpret results in context.

The developing brain is not endlessly resilient. Manganese overload is preventable. Test the water, review the formula choice, and keep iron stores up — three concrete steps that cost little and carry real protective value.

Concerned about your child's environmental exposures or attention difficulties? Speak with your pediatrician, and explore our guides to heavy metals and neurodevelopment at Avaneuro.

References

Tuschl, K., et al. (2017). SLC39A14 Deficiency. GeneReviews®. https://pubmed.ncbi.nlm.nih.gov/28541650/
Parmalee, N. L., & Aschner, M. (2016). Manganese and aging. Neurotoxicology. https://pubmed.ncbi.nlm.nih.gov/27293182/
Lucchini, R., et al. (2017). Manganese and Developmental Neurotoxicity. Advances in Neurobiology. https://pubmed.ncbi.nlm.nih.gov/28889261/
Bjørklund, G., et al. (2020). Interactions between iron and manganese in neurotoxicity. Archives of Toxicology. https://pubmed.ncbi.nlm.nih.gov/32180038/
Bjørklund, G., et al. (2017). Manganese exposure and neurotoxic effects in children. Environmental Research. https://pubmed.ncbi.nlm.nih.gov/28282629/
Song, Y., et al. (2025). Heavy metal exposure and cognitive impairment: An umbrella review of meta-analyses. Journal of Hazardous Materials. https://pubmed.ncbi.nlm.nih.gov/40966995/
Erikson, K. M., et al. (2007). Manganese neurotoxicity: a focus on the neonate. Pharmacology & Therapeutics. https://pubmed.ncbi.nlm.nih.gov/17084903/
Crinella, F. M. (2012). Does soy-based infant formula cause ADHD? Update and public policy considerations. Expert Review of Neurotherapeutics. https://pubmed.ncbi.nlm.nih.gov/22449212/
Zoni, S., & Lucchini, R. (2013). Manganese exposure: cognitive, motor and behavioral effects on children: a review of recent findings. Current Opinion in Pediatrics. https://pubmed.ncbi.nlm.nih.gov/23486422/
Liu, W., et al. (2020). Biomarkers of environmental manganese exposure and associations with childhood neurodevelopment: a systematic review and meta-analysis. Environmental Health. https://pubmed.ncbi.nlm.nih.gov/33008482/
Menezes-Filho, J. A., et al. (2009). Manganese exposure and the neuropsychological effect on children and adolescents: a review. Revista Panamericana de Salud Pública. https://pubmed.ncbi.nlm.nih.gov/20107709/
Iyare, P. U., et al. (2019). The effects of manganese exposure from drinking water on school-age children: A systematic review. Neurotoxicology. https://pubmed.ncbi.nlm.nih.gov/30797767/