Fluoride: very high levels in water associated with cognitive impairment in children

Fluoride: very high levels in water associated with cognitive impairment in children

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Fluoride is one of the more abundant elements naturally found in drinking water, and levels around 0.7mg per litre have been proven to reduce tooth decay. This is why some countries add fluoride to drinking water.

However, fluoride in drinking water is a controversial topic. There is concern about the potentially harmful effects of adding fluoride to our water and food. Scientists debate the pros and cons of fluoridation, and for many of us it may be hard to decide what conflicting scientific results mean for our health and that of our families.

When scientists reviewed all the evidence on the links between high fluoride and neurological problems, they found that damage to mental ability might exist for communities that use water with fluoride above recommended values. But it was not possible to show that it directly caused neurological disorder.

A new study from Tulane University in America adds to the debate. It suggests a link between high fluoride levels in water and cognitive impairment in children.

The study, published in the journal Neurotoxicology and Teratology, was based on 74 children in Ethiopia who were exposed to high fluoride in drinking water – averaging 7.6 milligrams per litre. This is well above the World Health Organization’s recommended limit of 1.5mg per litre.

In England, some local authorities adjust the level of fluoride to 1mg of fluoride per litre of water. And in the US, the maximum permitted amount in tap water is 4g per litre of water.

Higher levels of fluoride are already known to stain people’s teeth and cause brittle bones (called fluorosis). This latest study found that children drinking water with high levels of fluoride performed worse in tests designed to evaluate new learning and memory.


Rural communities in this part of Ethiopia, as well as in other developing countries, mostly rely on groundwater from a hand-pumped supply. Most families in this study have similar living conditions and culture. This offered the researchers a setting with restricted socioeconomic differences between children, but with a range of water supply fluoride between 0.4 and 15.5mg per litre.

The researchers tested memory and new learning in two ways. Children were asked to make three drawings from memory and worked with programs on tablet computers that test the way the brain manages learning and memory. The results of the tests were then compared with fluoride levels and other potential contaminants that influence the brain such as arsenic and lead. Only fluoride was substantially above existing recommended levels.

The graphs in the paper show data is scattered and does not follow an obvious straight line relationship between fluoride in drinking water and children’s abilities.

After detailed statistical analysis and adjustments of the data for demographics, health status and other likely influences, there were some tests where lower scores could be due to fluoride effects on cognitive abilities. But overall, most of the tests did not have consistent, statistically significant results.

Many studies that explore the health effects of natural or artificial environmental contaminants also find these relationships are not straightforward as there are so many differences between people.

The recent paper did not find a strong association between high fluoride in drinking water and the mental abilities of children aged five to 14 years. They found that high fluoride concentrations could account for around 5% of the variability in the children’s abilities, but the majority of the difference is due to other factors.

They advise that new advanced studies are urgently needed to better understand the links between mental development and fluoride exposure from the womb to adulthood.

Given that nearly 180 million people worldwide may be exposed to naturally elevated fluoride (many in Asia and Africa), more science is needed to establish if there are threshold levels where fluoride negatively affects health.

The Conversation

Robert.Kalin@strath.ac.uk has received funding from the NSF (USA), EPSRC (UK), NERC (UK), BBSRC (UK), Scottish Government, USAID, and UNICEF