Link suspected between manganese levels in water and IQ scores
Published Monday, September 20, 2010 1:22PM EDT
TORONTO - Children whose drinking water contains high concentrations of manganese appear to have lower IQ scores on average than children not exposed to the metallic element, researchers have found.
In a study of more than 350 children in southwestern Quebec rural communities dependent on tap water from wells, researchers found a striking correlation between manganese levels in the water and IQ scores.
"It's pretty straight-up," said lead author Maryse Bouchard, a researcher in environmental health at the University of Montreal.
"We saw that the average IQ decreased with increasing tap water manganese concentration," Bouchard said from Montreal. "And the difference between the least exposed and the most exposed was in the order of six IQ points, which is a very big difference."
However, Bouchard admitted to CTV Montreal's Cindy Sherwin that the practical effect of a six-point drop in IQ is difficult to quantify.
"Those six IQ points will not induce deficiencies to the point they will have learning difficulties," Bouchard said. "But actually, it depends. If a child already has a low IQ and add this deficiency, it could fall off to where you develop a learning deficiency."
The researchers, whose paper is published in Monday's issue of the journal Environmental Health Perspectives, tested tap water used by 251 families living in eight communities in an area roughly between Montreal and Quebec City. The tap water in Montreal is not included because the city has sophisticated filtration plants and does not rely on well water as a supply source.
The area had no industrial source of manganese, which is used in batteries, as plant fertilizer and as an alloy of steel. It is commonly found in groundwater due to leaching from minerals and rocks.
Neuropsychologists gave a battery 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 also estimated 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.
But it can be a potent neurotoxin in high concentrations, and occupational and environmental exposure to air-borne manganese has been linked to neurological deficits in both children and adults. Manganese is believed to interfere with neurotransmitters like dopamine and serotonin, which are "important for proper cognitive functioning," Bouchard said.
The amount of manganese in drinking water is not regulated in Canada or the United States, although health-based recommendations for maximum levels are set at 400 micrograms per litre by the World Health Organization and 300 mcg/l by the U.S. Environmental Protection Agency.
While a small proportion of children involved in the 2007-2009 study had drinking water with manganese concentrations above those guidelines, "96 per cent of our children were exposed to levels that are supposed to be safe," said Bouchard.
Tests of the hair samples taken from the children suggests the substance persists in the body over time.
Although the study design didn't allow researchers to determine at what point neurological effects occurred, Bouchard said exposure to high manganese levels was likely both fetal _ when mothers consumed the water while pregnant _ and when children drank the water themselves.
However, "the dose-response relationship that is demonstrated is so clear, it suggests that current exposure is really associated with the cognitive deficits and not necessarily only to past exposure," she said.
Manganese can be removed through household filtering processes, said Bouchard, who advises families in homes reliant on wells to have their water tested.
The study's authors, including researchers at the University of Quebec at Montreal and Ecole Polytechnique de Montreal, say national and international guidelines for safe manganese levels in water should be reconsidered.
Some factors overlooked: expert
McGill chemistry professor Joe Schwarcz said while he believe it's a solid study, much more research is needed.
"What I would really like to see a controlled (study) for is not individual nutrients in food, but overall nutritional status. Is it possible that the children who have lower IQ in the study were in fact in some way of a poorer nutritional status?" he said.
While researchers examined income, maternal intelligence and education, intelligence depends on many criteria said Schwarcz.