Excess manganese implicated as cause of impaired childhood intellectual functioning

The human body needs trace amounts of manganese, but excess levels are toxic to brain cells. Evidence suggests that elevated manganese levels can contribute to violent behavior (see related article, Crime Times, 1996, Vol. 2, No. 2, Page 3), and a new study indicates that high manganese intake can impair intellectual function in children.

Gail Wasserman and colleagues evaluated 142 ten-year-old children in Bangladesh who consumed well water containing varying amounts of manganese. The researchers controlled for levels of arsenic, because an earlier study linked arsenic in drinking water to impaired intellectual functioning.

Wasserman and colleagues asked the children to perform six intellectual tests (similarities, digit span, picture completion, coding, block design, and mazes) and used the results to calculate verbal, performance, and full-scale intelligence scores. The tests were adapted from a standard IQ test, in order to be relevant to the rural Bangladeshi children.

The researchers divided the children into four groups based on manganese exposure via drinking water. and found significant reductions in verbal, performance, and full-scale intelligence scores for children in the highest-intake group (manganese higher than 1,000 micrograms per liter), compared to those in the lowest-intake group (manganese lower than 200 micrograms per liter). Smaller decrements in performance and full-scale intelligence scores were detected in children in the intermediate-manganese groups.

The researchers say their findings are relevant to children in the United States, because about 6% of domestic wells contain manganese concentrations higher than 300 micrograms per liter, a level at which some impairment was detected in the Bangladeshi children. They also say, "It is interesting to note that although breast milk contains between 3 and 10 micrograms of manganese per liter, infant formulas have been reported to contain as much as 50 to 300 micrograms per liter. Our findings, coupled with the absence of reports of manganese deficiency in young children, led us to conclude that the possible consequences in children of excess exposure to manganese from water, diet, and gasoline additives deserve further attention."

"Water manganese exposure and children's intellectual function in Araihazar, Bangladesh," Gail Wasserman, Xinhua Liu, Faruque Parvez, Habibul Ahsan, Diane Levy, Pam Factor-Litvak, Jennie Kline, Alexander van Geen, Vesna Slavkovich, Nancy J. Lolacono, Zhongqi Cheng, Yan Zheng, and Joseph Graziano, Environmental Health Perspectives, Volume 114, Number 1, January 2006, 124-9. Address: Gail A. Wasserman, New York State Psychiatric Institute, 1051 Riverside Drive, Unit 78, New York, NY 10032, wassermg@childpsych.columbia.edu.