Table 4 Summary of results from studies examining manganese in teeth

Ericson et al. (2007) [52]

Children from a maternal prenatal cohort that provided shed molars at 11–13 years. Mn concentrations from teeth enamel were measured but values not reported.

None measured

Prenatal Mn levels, representing exposures from the 20^th gestational week were positively associated with behavioral outcomes: higher levels of disinhibition (36 months), impulsivity (4.5 years), externalizing and internalizing problems (1^st and 3^rd grades) and disruptive behaviors (3^rd grade). No differences on standardized tests of cognitive ability or achievement. Analyses were adjusted for mothers’ education, family income and child ethnicity. Postnatal Mn levels, representing exposures from gestational weeks 62–64, only correlated with teachers’ reports of externalizing behaviors (1^st and 3^rd grades).

No association between pre- and postnatal Mn (r = 0.13, NS [1]), Mn and Pb (prenatal r = 0.09, NS; postnatal r = -.08, NS).

A significant association was seen with prenatal Mn and Fe (r = 0.74, p < 0.001) but not postnatal Mn (r = - .06, NS).

Gunier et al. (2015) [45]

Children from a maternal prenatal cohort provided shed teeth starting at age 7. Mn from dentin of deciduous teeth [2]

Prenatal: 0.51 (0.19)

Postnatal:

0.20 (0.23).

Not reported, but related to residential proximity or use of agricultural fungicides with Mn.

Prenatal Mn levels were not associated with MDI or PDI at 6, 12 or 24 months and no interactions by sex.

A two-fold increase in postnatal dentin- Mn levels was associated with small, significant decreases in MDI at 6 and 12 months (but NS at 24 months). Postnatal dentin-Mn levels were inversely related (but NS) with PDI scores at 6 months, but not 12 or 24 months.

Effect modification by sex was reported with significant interactions between prenatal Mn and maternal hemoglobin (HGB) in girls at 6 months.

Girls whose mothers had lower prenatal hemoglobin (HGB, <11.6 g/dL) had a decrease of 10.5 points (95%CI: -16.2, -4.8; n = 38) on the MDI and 11.6 points (95%CI: 19.3, -3.9) on the PDI per two-fold increase in prenatal Mn at 6 months.

No interactions with blood-Mn and blood-Pb observed or any relationships with neurodevelopment at 24 months.

Mora et al. (2015) [39]

Children from two integrated prenatal cohort samples provided teeth at 7–9 years.

Mn from dentin of deciduous teeth: Prenatal: 0.46 (1.48);

Postnatal: 0.14 (2.47)

None reported, but exposure related to agricultural exposures to Mn-containing fungicides.

Behavior: No significant associations for prenatal Mn and behavioral outcomes in children ages 7, 9 or 10.5 years. Higher postnatal Mn was significantly associated with maternal reports of hyperactive, internalizing and externalizing behaviors for children aged 7 years, but not at older ages.

Cognition: Neither prenatal nor postnatal Mn was consistently and significantly associated with cognitive outcomes. A sex effect was shown only for boys with a positive, significant relationship between postnatal Mn and cognitive scores (full scale, verbal comprehension, and perceptual reasoning IQ) at ages 7 and 10.5 years, and working memory IQ at 7 years.

Memory: Higher prenatal dentin Mn levels associated with significantly better memory scores for children ages 9 and 10.5 and in sex stratified analyses. Postnatal Mn levels were not associated with memory scores in analyses of all children. Sex-stratified analyses revealed higher Mn significantly associated with better memory scores at 9 and 10. 5 years in boys.

Motor function: No consistent, significant associations of prenatal Mn with motor function for all children. Sex-stratified analyses showed higher dentin Mn levels significantly associated with better motor function only in boys (finger tap Z-score at 7 years), Luria-Nebraska Motor Scale at 10.5 years). Postnatal Mn levels showed no consistent, significant associations for all children, but sex effects show higher dentin Mn levels associated with significantly better motor function scores only in boys at 7 years.

Higher prenatal Mn levels were associated (NS) with poorer visual spatial memory outcomes at 9 years and poorer cognitive scores at 7 and 10. 5 years in children with higher Pb levels (≥0.8 μg/dL).