Fluoride in drinking water raises concerns for brain development

Water keeps us alive, but what happens when something meant to help us raises new concerns? For decades, governments have added fluoride to drinking water to protect teeth, believing it to be a simple solution for cavity prevention.

However, a recent study from Karolinska Institutet in Sweden suggests fluoride exposure – especially in pregnancy and early childhood – could impact brain development.

It’s not the first time this issue has surfaced, but the findings add weight to a long-standing debate.

Fluoride in drinking water

Naturally occurring fluoride is present in many water sources, but its levels are often too low to significantly prevent cavities.

To address this, countries such as the USA, Canada, Chile, Australia, and Ireland have long introduced fluoride into their public water systems. The standard level used in these nations hovers around 0.7 mg per liter, which is considered optimal for dental health benefits.

Despite its widespread use, the addition of fluoride to drinking water has remained a topic of debate. Health officials argue it is a cost-effective public health measure, but concerns about potential side effects persist.

“Given the concern about health risks, the addition of fluoride to drinking water is controversial and has been widely debated in the USA and Canada,” said Maria Kippler, associate professor at Karolinska Institutet.

“Our results support the hypothesis that even relatively low concentrations of fluoride can impact children’s early development.”

Tracking fluoride exposure

To understand how fluoride affects brain development, scientists focused on a rural area in Bangladesh. Here, fluoride naturally seeps into the water supply, just like in many other regions worldwide. They followed 500 mothers and their children for years.

By studying these families over time, researchers could observe how fluoride exposure influenced thinking and learning.

The scientists tested urine samples to check fluoride levels in mothers and children. Unlike toothpaste, which isn’t swallowed, most fluoride comes from drinking water and food.

When the children turned five and ten, the researchers tested their cognitive abilities using trusted psychological methods. The goal was to see if fluoride levels played a role in shaping their thinking and reasoning skills.

Fluoride exposure and its effects

The findings were concerning. The median concentration of fluoride in the urine of pregnant women in the study was 0.63 mg/L. Higher levels of fluoride in mothers were linked to lower cognitive abilities in their children at both five and ten years old.

“I’d like to stress that dental care products such as toothpaste are not normally a significant source of exposure since they are not intended for ingestion,” said Dr. Kippler.

“Fluoride in toothpaste is important for prevention of caries, but it’s important to encourage small children not to swallow the toothpaste during brushing.”

At age ten, children with more than 0.72 mg/L of fluoride in their urine showed significant cognitive deficits compared to those with lower levels. The most affected areas were verbal reasoning and sensory processing, essential skills for learning and communication.

Alarmingly, these effects were observed at fluoride levels below the current World Health Organization (WHO) and European Union (EU) drinking water safety threshold of 1.5 mg/L.

Complex impact on development

Surprisingly, fluoride levels in five-year-olds did not strongly correlate with cognitive abilities. “This may be due to the shorter exposure time,” said Dr. Kippler.

“But also to the fact that urinary fluoride concentrations aren’t as reliable in younger children owing to greater variations in how much fluoride is taken up and stored in the body, particularly in the bones.”

Perhaps younger children process fluoride differently, or maybe it takes longer for the effects to become noticeable. Either way, this part of the study highlights how complex fluoride’s impact on development might be.

Long-term effects of fluoride

The study found strong links, but it can’t prove fluoride directly causes these effects.

To fully understand how fluoride affects cognitive abilities, more longitudinal studies are needed. The researchers plan to examine this issue in other populations and develop experimental models to explore the potential biological mechanisms at play.

“There is a need for more research to create a robust basis for reviewing fluoride health risks and thresholds for drinking water, foods, and dental care products, especially for children,” said Dr. Kippler. “Even small changes in cognition at a population level can have serious public health consequences.”

Since many people are exposed to fluoride, it’s important to understand its risks. Protecting teeth matters, but experts must also consider if fluoride affects brain development.

This study received financial support from the Swedish Research Council and the Swedish Research Council for Environment, Agricultural Sciences, and Spatial Planning (FORMAS).

The study is published in the journal Environmental Health Perspectives.

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