Fluoride Action Network

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Bone Fracture

“One cannot help but be alarmed by the negative effects of fluoride on bone strength consistently demonstrated in animal models.” - Dr. Charles Turner, Indiana University.

Bone Fracture

No one disputes that high doses of fluoride wreak havoc on bone tissue. Millions of people throughout the world, for example, currently suffer a debilitating bone disease called skeletal fluorosis, which is caused by fluoride. For many years, however, fluoride advocates believed that fluoride could also benefit bone due to its ability, under certain circumstances, to increase bone mass. Attempts to use fluoride as an experimental treatment for osteoporosis, however, resulted in more fractures, not less.

More recently, studies of human populations have reported increased fracture rates in communities with 4 mg/L fluoride in the water, and animal studies have consistently found reductions in bone strength from fluoride exposures. Although an increased fracture risk has not been consistently demonstrated at the fluoride levels (0.7-1.2 mg/L) added to water in fluoridation programs, the current weight of clinical, animal, and epidemiological evidence suggests that some individuals in fluoridated communities — particularly those with kidney disease — will suffer fragile bones as a result of their overall fluoride intake, including from fluoridated drinking water.

Clinical Trials: High-Dose Fluoride Increases Fracture Rates

For many years, however, fluoride advocates believed that fluoride, under controlled conditions, could benefit bone due to its ability to increase bone mass. In the 1960s, scientists began using fluoride as an experimental drug for the treatment of osteoporosis. Instead of reducing the number of fractures, however, numerous clinical trials reported that the fluoride treatment increased the rate of fractures (particularly hip fractures) and caused a number of other side effects, including gastric distress and joint pain. Based on these results, the FDA rejected the use of fluoride as a medical treatment for treating osteoporosis.

Animal & In Vitro Studies: Fluoride Exposure Weakens Bone

Consistent with the clinical trials, numerous animal and in vitro studies have reported that bone strength declines with increased fluoride exposure. As noted in the Journal of Bone and Mineral Research,

“[O]ne cannot help but be alarmed by the negative effects of fluoride on bone strength consistently demonstrated in animal models.” (Turner 1995)

Epidemiological Studies:

Fluoride at 4 mg/L Increases Fracture Risk

Following the disastrous results of the experimental trials, researchers began investigating whether current fluoride exposures in the population could pose a similar risk. Although the clinical trials had used high doses of fluoride (20 to 34 mg per day), the trials only lasted for short periods of time (6 months to 4 years). It stands to reason, therefore, that people exposed to lower levels of fluoride for much longer periods of time could be at risk as well.

To determine this, investigators began comparing the bone density and bone fracture rates of communities with varying levels of fluoride in the water. Two consistent findings from these studies emerged: fluoride levels in drinking water (4 mg/L) that are still considered “safe” by the EPA reduce the density of cortical bone and increase the bone fracture rate in a population. Based in part on this research, the U.S. National Research Council (NRC) called on EPA to reduce the allowable levels of fluoride in water. EPA has yet to do so.

Fluoride at 1 mg/l: Mixed Evidence of Fracture Risk

A number of studies have sought to determine whether fluoridated drinking water (1 mg/L) also increases the risk of bone fracture. The results of these studies have been mixed, with some studies finding increases in bone fracture, other studies finding no effect, and others finding reductions in fracture risk. As noted by scientists on both sides of the fluoride debate, however, the usefulness of these studies is limited. Most of the studies, for example, only examined older populations that had no exposure to fluoridated water during their childhood (the period of life with the highest rate of fluoride accumulation in bone). Most of the studies, in fact, involved adult populations with less than 20 years of exposure to fluoridated water. The available epidemiological studies on fluoridation and bone fracture provide few definitive answers about the impact of lifetime exposures to artificially fluoridated water.

Water Fluoridation: A Very Narrow Margin of Safety

In the NRC’s 2006 review, it noted that there is “suggestive” evidence that the risk of bone fracture increases as the fluoride levels increase from 1 to 4 mg/L. The following figure comes from one of the studies that the NRC cited as providing evidence of a fracture risk below 4 mg/L:

Prevalence of hip fractures and fluoride concentration in drinking water in six Chinese populations since the age of 20 years. (SOURCE: Li 2001).

As this figure shows, the risk of hip fracture in these populations more than doubled at fluoride levels between 1 and  2.2 ppm. Although this increase was not statistically significant, it suggests the existence of a very narrow margin of safety between the level of fluoride added to water for the prevention of tooth decay and the level of fluoride that weakens bone.

The lack of a safety margin is amplified when considering the relatively low doses of fluoride that the populations in this study were ingesting. These doses are displayed in the following figure:

Daily Dose of Fluoride Associated with Hip Fracture Risk (SOURCE: Li 2001).

As can be seen, the risk of hip fracture was distinctly elevated in populations with an average dose of just 6 to 8 mg per day. To put this in perspective, the Department of Health and Human Services has estimated that adults living in fluoridated communities in the U.S. generally ingest between 1.6 and 6.6 mg of fluoride per day. (DHHS 1991). This dose range overlaps the doses associated with hip fracture risk.

A Clear Risk for Kidney Patients

A narrow margin of safety is especially problematic when considering that some subsets of the population, particularly those with advanced kidney disease, have a heightened vulnerability to fluoride. Because people with kidney disease have an impaired ability to excrete fluoride, they accumulate higher levels of fluoride in their bone than healthy individuals. Because of this, kidney patients can be harmed at doses well below those that cause harm in others. Recent research, for example, has found that dialysis patients in fluoridated areas (Ng 2004) accumulate levels of fluoride in their bone that can worsen, if not cause, osteomalacia — a bone-softening disease that causes bones to fracture.

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