In a study of more than 350 children in Quebec communities dependent on tap water from wells, researchers found a striking correlation between manganese levels in the water and IQ scores.
Researchers tested tap water used by 251 families living in eight communities in an area roughly between Montreal and Quebec City.
They gave a range of tests to 362 children aged six to 13 taking part in the study to determine their general cognitive abilities, including verbal, visual-spacial and concept-formation skills. The researchers estimated children's manganese intake from water ingestion as well as diet, using a food frequency questionnaire.
Manganese is an essential nutrient and is found in a wide variety of fruits, vegetables and grains. While small amounts are needed for proper health, in high concentrations, it can lead to neurological deficits in both children and adults.
Manganese is believed to interfere with neurotransmitters like dopamine and serotonin, which are vital for proper cognitive functioning.
Researchers found that the average IQ decreased with increasing tap water manganese concentration. The difference between the least exposed and the most exposed was in the order of six IQ points.
The findings were published in today's issue of the journal Environmental Health Perspectives.
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