Drinking fluoridated water does not lower IQ, according to a new study by researchers from the University of Otago in New Zealand.

Many popular theories cast suspicion on the role of water fluoridation, with some people claiming that fluoridated water is associated with a range of adverse health outcomes.

Fluoride is routinely added to drinking water in the US and other countries as a supplement to safeguard against tooth decay. However, some people object to the compulsory nature of water fluoridation.

Also, some of the concern around water fluoridation stems from conspiracy theories relating to the end of World War II. These include suggestions that the Nazi regime secretly fluoridated water supplies in an attempt to damage the pineal gland of their citizens, which some people think promotes docility in humans.

The proximity of conspiracy theories to the issue has made the debate over health risks of water fluoridation contentious. However, in 2012, researchers from Harvard University in Cambridge, MA, cast doubts on the health benefits of fluoride in water supplies.

They conducted a review of studies looking at the effects of water fluoridation on children and found that children living in high-fluoride areas “had significantly lower IQs than those who lived in low-fluoride areas.”

Fluoride, the researchers said, is a chemical “with substantial evidence of developmental neurotoxicity.”

However, these findings are challenged by a new study published in the American Journal of Public Health.