Editor's note: The following letter was received in response to a recently published article. We are always willing to listen to our audience and publish their thoughts.
DrBicuspid got it right and if anything, understated the strength of a recent study finding that "Combined fluoride and lead exposure reduced bone health in youth."
A letter to the editor claiming the study was “weak science” selectively quotes from the study and misinterprets its findings. The authors of the study emphasized that looking at the bone effects of fluoride or lead in isolation misses the synergistic effect they found from combined fluoride and lead exposure. The study found that co-exposure produced much greater reduction in adolescents' bone mineral density (BMD) than the sum of the individual effects of fluoride and lead. Far from being a “potential” interaction, this synergistic effect was highly statistically significant, of large magnitude, and based on a nationally representative sample of over 2,000 children, after controlling for many possible confounding factors.
There is nothing “speculative” about what the study found. Here's what the authors report, in their own words:
“Although the trend in BMD changes is inconsistent when exposed to lead or high levels of fluoride individually, the combined inhibitory effect on BMD is significantly greater than the sum of their individual effects in the combined exposure scenario. This finding suggests that combined exposure to fluoride and lead exerts a negative synergistic effect on BMD.” [emphasis added]
“This study indicates that co-exposure to fluoride and lead poses a significant threat to adolescent bone health. Adolescence is a critical period for the rapid accumulation of BMD, and both fluoride and lead can adversely affect BMD .... It is particularly concerning that simultaneous exposure to low doses of fluoride and lead may significantly exacerbate bone impairment.”
The study’s overarching finding was a clear adverse effect on BMD from combined exposure to fluoride and lead that was significantly greater than the sum of their individual effects.
This raises important questions:
Exactly how much greater was the combined effect than the summed individual effects? Even more to the point, by how much was BMD reduced in children exposed to fluoride levels common from artificial fluoridation and elevated lead levels experienced by substantial numbers of children in the US? Is the decrease in BMD in this group of children enough to matter clinically? Will it increase their risk of bone fractures in childhood and/or adulthood?
The answers:
Compared to children with low fluoride and low lead exposures, the study predicts children with exposures common in fluoridated areas and who also have elevated blood lead levels could suffer an approximate 10% reduction in BMD. This is a clinically large effect. Such a reduction in BMD in children has been associated with an approximate 15% to 30% higher risk of broken bones, including forearm fractures, the most common type in children.* This may also explain the findings of the sole study of fluoride and bone fractures in US children done to date. That study found 3-fold higher fracture rates in states with the greatest percentage of their population fluoridated or greater average water fluoride concentration [Lindsay 2023].
Furthermore, reductions of BMD in adolescence have life-long consequences. Adolescence is when much of the accrual of bone mineral occurs that will have to last a lifetime. Therefore, a deficit in adolescence can increase the risk of osteoporosis and deadly hip fractures in older adulthood, as described by researchers studying the trajectory of bone accumulation across life stages:
“The importance of maximizing bone mineral accrual during the growing years is clearly recognized. For example, it has been reported that 60% of the risk of osteoporosis can be explained by the amount of bone mineral acquired by early adulthood. Childhood and adolescence is a particularly important time to maximize bone accrual because the skeleton undergoes rapid change owing to the processes of growth, modeling, and remodeling.” [Baxter-Jones 2011]
While a single observational study can’t prove a causal relationship, it is a rigorous study using high-quality data and is the first to test the possibility that co-exposure to fluoride and lead can cause more harm to developing bone than the sum of the two, a synergistic effect. For dentists to mischaracterize, downplay, or outright dismiss the study because it raises serious questions about the safety of water fluoridation ... that is unscientific.
Sincerely,
Chris Neurath
Research Director
American Environmental Health Studies Project (AEHSP)
* References and detailed calculations for the derivation of the 10% reduction in BMD and its consequent 15% to 30% increased risk of bone fracture are available in a supplement. The 10% reduction in BMD is based on comparing those with lower exposure to fluoride and lead, defined as the 10th percentile exposures, to those with higher exposure to both, defined as the 90th percentile exposures.
