High prenatal manganese linked to behavior problems

Prenatal exposure to high levels of manganese is linked to an increased risk for a wide range of behavior problems, according to a new study.

Jonathon Ericson and colleagues tested shed molar teeth from 27 children between the ages of 11 and 13, all participants in a long-range study of child development. The researchers note that tooth enamel provides a good measure of manganese accumulation over a long period, "analogous to levels of pollutants recorded in tree rings." The cusp tip of the first molar, they say, provides a record of manganese exposure during the 20th week in utero, while the root tip of the molar provides a record of exposure seven months after birth.

As part of the overall study, the researchers evaluated children's behaviors using different methods at different ages. The evaluations included:

• The "Forbidden Toy Task," a measure of the ability to inhibit impulsive reactions by obeying a request to avoid a particular toy, administered when the children were three years old.
• The Mirsky Continuous Performance Test (CPT), administered at 54 months of age to measure sustained attention and impulse control.
• The Children's Stroop Test, also given at 54 months to measure the ability to inhibit incorrect behavior.
• Questionnaires about the children's behavior filled in by parents and teachers when the children reached 1st and 3rd grades.

Manganese levels at the age of seven months correlated with later behavior problems only on the teachers' evaluations, suggesting that exposure at this age had less effect. IQ tests did not correlate with manganese levels-an expected finding, the researchers say, because animal studies indicate that excess manganese affects behavior but not intelligence.

Ericson and colleagues say the effects of manganese may stem from its effects on the dopamine system. Altered dopamine levels are strongly linked to impulsivity and ADHD, and a recent study led by Francis Crinella (who also participated in the current study) found that exposing rats during infancy to high levels of manganese led to depletion of dopamine in a brain area associated with ADHD.

The researchers suggest that some children are over-exposed to manganese before birth because their mothers are iron-deficient. Iron deficiency, which affects more than half of all pregnancies worldwide, can cause excess absorption of manganese.

One potential source of significant amounts of manganese after birth is soy infant formula, which can contain as much as 80 times the amount of manganese as breast milk (see related article, Crime Times, 1999, Vol. 5, No. 1, Page 3).