Fluoride in drinking water: the link to children's IQ according to a US government study

The report did not attempt to quantify exactly how many IQ points might be lost at different levels of fluoride exposure. But some of the studies reviewed in the report suggested that IQ was 2 to 5 points lower in children who had had higher exposures.

Since 2015, federal health officials have recommended a fluoridation level of 0.7 milligrams per litre of water, and for five decades before that the recommended upper range was 1.2. The World Health Organisation has set a safety limit for fluoride in drinking water of 1.5.

The report states that about 0.6% of the US population - about 1.9 million people - use water systems with fluoride levels of 1.5 milligrams or more.

"The findings of this report raise questions about how these people can be protected and what makes the most sense to dow," said Malin.

The 324-page report did not come to a conclusion on the risks of lower levels of fluoride in water, stating that further studies are needed. It also did not explain what high levels of fluoride might cause in adults.

The American Dental Association, which supports water fluoridation, had been critical of earlier versions of the research conducted by Malin. When asked for comment, a spokesman sent an e-mail late Wednesday afternoon informing that the organisation's experts were still reviewing the report.

Fluoride is a mineral that exists naturally in water and soil. About 80 years ago, scientists discovered that people whose water supplies naturally contained more fluoride also had less tooth decay, triggering a push to convince more Americans to use fluoride for better dental health.

In 1945, Grand Rapids, Michigan, became the first city in the United States to start adding fluoride to tap water. In 1950, federal officials approved water fluoridation to prevent tooth decay and continued to promote it even after fluoride toothpaste brands came on the market several years later. Although fluoride can come from many sources, drinking water is the main source for Americans.

Officials lowered the recommendation on fluoride levels in drinking water in 2015 to address a tooth condition called fluorosis, which can cause stains on teeth and was becoming increasingly common in the US. children.

Separately, the Environmental Protection Agency has established a requirement that water systems may contain no more than 4 milligrams of fluoride per litre. This standard is designed to prevent skeletal fluorosis, a potentially disabling disease that causes weaker bones, stiffness and pain.

But more and more studies have pointed to a different problem, suggesting a link between higher fluoride levels and brain development. Researchers have questioned the impact on the development of foetuses and very young children who might ingest tap water with infant formula. Animal studies have shown that fluoride could impact neurochemical cell function in brain regions responsible for learning, memory, executive functions and behaviour.

In 2006, the National Research Council, a private non-profit organisation based in Washington, D.C., stated that limited evidence from China indicated neurological effects in people exposed to high levels of fluoride. The organisation called for further research into the effects of fluoride on intelligence.

After further research continued to raise doubts, in 2016 the National Toxicology Programme began work on a review of available studies that could provide insight into the need for new fluoride restriction measures. (f.s.)