RFK Jr's Claims About Paracetamol During Pregnancy And Water Fluoridation Have Just Been Proven Wrong, Again

Following evidence in the 1930s and 1940s that people who grew up in locations with slightly elevated fluoride in the water had stronger teeth, many cities started adding fluoride to the water. Opposition quickly spread fanned by a mix of claims that ranged from the plausible but unproven to the utterly ridiculous. RFK Jr added fuel to the fire last year when he told the Centers for Disease Control and Prevention to stop recommending fluoride.

Paracetamol has much more recently become the target of attacks, with President Trump last year alleging the taking of Tylenol®, the leading brand of paracetamol in the US, during pregnancy is driving increased rates of autism diagnosis. RFK Jr has supported the claims.

Neither claim had much in the way of scientific evidence behind it, aside from research on the harms of fluoride at concentrations far higher than those used in water supplies.

The first of the new studies also examines water fluoridation, specifically in Wisconsin. The state has conducted a long-running project, comparing life outcomes of students who graduated high school in 1957, including where they lived at ages 1 and 11. Members of the graduating class still living in the state have been encouraged to take cognition tests at 53, 64, 72 and 80 years old, with their results recorded for research purposes.

A team of researchers used this data to compare IQ estimates at 16 and in late adulthood, for 3,614 Wisconsin residents who never lived for an extended time in areas with fluoridated water and 2,595 who were exposed to fluoridated water from birth. Samples of more than 2,000 residents of the state who started drinking fluoridated water by ages 8 and 14 were also included.

There were no significant IQ differences between any of these groups, but those who didn’t get fluoride performed worst at all ages. The authors controlled for factors such as parental education, none of which changed the results.

The findings reinforce the findings of a study published last year by some of the same authors that compared exam results for high school students who had grown up in areas with and without fluoridation. After accounting for factors such as socioeconomic background, that paper reported test scores were slightly higher in fluoridated areas, although the authors did not go so far as to say the fluoride was actually boosting brain power.

The authors of the new study acknowledge they could not directly measure the subjects’ exposure to fluoride, for example by taking urine samples. Nevertheless, if growing up in areas with fluoridated water has no ill-effects on average, it is hard to see what the problem is.

Meanwhile, many studies have shown the benefits of fluoridation for teeth. It is sometimes argued that the development of fluoridated toothpaste has done away with the need to fluoridate the water supply. However, Calgary’s experience of a steep rise in dental decay when fluoridation stopped, leading to its return, indicates fluoridation remains beneficial. Utah and Florida have recently ended fluoridation, and may come to suffer the same consequences.

The second study, which involves all children born in Denmark between 1997 and July 2022, other than in multiple births, has compared whether their mothers were prescribed paracetamol during pregnancy. It also broke the sample down by the trimester when the prescription was given, and the daily dosage.

Of the children whose mothers did not take paracetamol during pregnancy, 3 percent were diagnosed with autism during the study period. For those whose mothers were prescribed the painkiller, the percentage was just 1.8 percent. That might give the impression paracetamol is associated with reduced autism diagnosis, however, once the authors controlled for factors like the mother’s age, the autism rates were slightly higher among those prescribed the drug. The difference was not even close to statistical significance. Even high daily paracetamol doses showed no significant relationship to diagnosis rates.

In Denmark, as in most countries, paracetamol is available over the counter, so some mothers may have been taking it without prescription. However, their daily dosage would probably have been lower than those with a prescription. This is particularly the case for children born after 2013, when Denmark limited the amount of paracetamol that could be bought at one time. The restriction does not appear to have had any effect on autism rates.

The credibility of RFK Jr’s claims in relation to paracetamol was particularly low, given his apparently poor understanding of the diagnosis. Kennedy claimed in a press briefing last year that children with autism “will never pay taxes. They'll never hold a job. They’ll never play baseball. They’ll never write a poem. They’ll never go out on a date.” This was news to millions of autistic people worldwide who have done many or all of those things, although getting presumably the job and date part became harder after such a campaign of stigmatization.

The fluoridation study is published in Proceedings of the National Academies of Science. The research on paracetamol (using the alternative name acetaminophen) is published in JAMA Paediatrics.