For decades, fluoride has been a cornerstone of dentistry and public health, widely recognized for its ability to protect against tooth decay. In Australia, for instance, more than 90% of the population has access to fluoridated tap water, a program scientifically proven to be safe and effective. However, a recently published meta-analysis has sparked media attention by suggesting a link between higher fluoride exposure and lower intelligence quotient (IQ) in children. This finding has understandably caused concern among the public. But how should we interpret these results? According to Professor Loc Do, an expert in dental public health, a closer look at the data reveals that the findings are not a reason to worry about the fluoride levels in public water supplies. The review is based on a body of research with significant limitations, and its conclusions do not apply to controlled fluoridation programs in developed nations.
A Long-Standing Controversy
Tooth decay, a common and often painful condition, can have serious negative effects on both dental and overall health. Fluoride has been scientifically proven to strengthen teeth, making them more resistant to decay. This has led to the widespread adoption of water fluoridation as a safe, effective, and equitable public health measure to improve oral health on a population-wide scale. Despite this scientific consensus, the practice has historically been a subject of controversy.
The potential link between fluoride and IQ has been a contentious topic for over a decade. Early concerns were raised by studies conducted in China and India. However, it is crucial to note that these studies were criticized for their poor methodology. Water in these regions had naturally occurring fluoride levels that were many times higher than the precise, low levels used in water fluoridation programs. The studies also failed to control for other contaminants in the water supply. Despite more recent reviews focusing on the levels of fluoride used in public water systems concluding that fluoride is not linked to lower IQ, some have continued to raise concerns.
A review by the United States National Toxicology Program, for instance, failed to pass a quality assessment by the US National Academies of Sciences, Engineering and Medicine due to significant limitations. The authors of that review later published their findings independently in the journal JAMA Paediatrics, and it is this study that has been generating the recent media attention.
Questionable Data Quality
The study in question was a systematic review and meta-analysis that evaluated 74 studies from around the world. However, a deep dive into its methodology reveals significant flaws. A staggering 52 of the 74 included studies were rated as having a high risk of bias. Furthermore, 64 of them were cross-sectional studies, which can observe a correlation but are fundamentally unable to establish a causal relationship.
The geographical distribution of the studies is also a major concern. The vast majority were conducted in developing countries such as China (45), India (12), Iran (4), Mexico (4), and Pakistan (2). Only a handful were from developed countries with established public water systems, where regular monitoring ensures water quality. The data largely came from populations with high to very high levels of natural fluoride, not from controlled water fluoridation programs where levels are carefully regulated. Consequently, while the review concluded there was an inverse association between fluoride and IQ, the low quality and irrelevance of the included data cast serious doubt on its conclusion.
The Confounding Factor of Fluoride Levels
One of the most critical limitations of the meta-analysis is its failure to properly differentiate between uncontrolled, high natural fluoride levels and the controlled, low levels used in public water systems. For instance, the review found that there was no significant association with IQ when fluoride was measured at less than 1.5 mg per liter in water. In Australia, the recommended levels in public water supplies range from just 0.6 to 1.1 mg/L, well below that threshold.
The method for collecting IQ scores also varied widely among the studies, further compromising the validity of the meta-analysis’s combined results. While this is a common challenge in research on this topic, the lack of consistency in this particular review raises additional doubts. It’s also noteworthy that several included studies from countries with controlled public water systems—such as Canada, New Zealand, and Taiwan—showed no negative effects, yet these findings were largely overshadowed by the poor-quality data from other regions.
No Cause for Alarm
While the review did not include any studies from Australia, the country has its own robust body of research on the topic. Professor Loc Do has been involved in population-based longitudinal studies investigating the link between fluoride exposure in early childhood and child development. The IQ data in these studies was collected by trained psychologists to ensure quality and consistency. Both studies provided strong evidence that fluoride exposure in Australia does not negatively impact child development.
This new review is therefore not a reason for public concern in Australia or other developed countries with well-established water fluoridation programs. Fluoride remains a cornerstone of public health, and its proven ability to reduce tooth decay is particularly important for vulnerable populations. While high and uncontrolled levels of natural fluoride in less developed countries do warrant attention, and programs are underway to address this, the evidence supports the continued use of fluoride in controlled public water supplies. The perceived link between fluoride and lower IQ, in this context, appears to be little more than a false alarm.
