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)
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:
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:
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.
Study finds link between tea, fluoride, and weak bones
The authors identified 5 patients in their practice who developed skeletal fluorosis as a consequence of drinking tea (primarily darjeeling tea) over a course of 10 to 25 years. The skeletal fluorosis in these patients was the osteomalacic variety of the disease, in which the bones become softened and weak. As a result of the “fluoride-related osteomalacia”, the patients suffered “spontaneous bone fractures” where their bones fractured without external trauma.
Ministry of not-so-funny walks
The fluorosis problem is "enormous, unbelievable," says Andezhath Susheela of the Fluorosis Research and Rural Development Foundation in Delhi. She has been unravelling the national story for a decade during which time her estimate of the number of people leading "a painful and crippled life" from fluorosis has risen from one million to 25 million and now to 60 million -- six million of them children.
Fluoride Reduces Bone Strength in Animals
Most animal studies investigating how fluoride effects bone strength have found either a detrimental effect, or no effect. Few animal studies have found a beneficial effect. In fact, one of the few studies that found a beneficial effect was unable to be repeated by the same authors in a later
Fluoride Exposure Increases Metabolic Requirement for Calcium & Vitamin D
It is well known that individuals with nutrient deficiencies are more susceptible to fluoride toxicity, including fluoride's bone effects. As discussed in the following studies, fluoride increases the skeleton's need for calcium (and vitamin D) by increasing the amount of unmineralized tissue (osteoid) in the bone. When insufficient calcium and
Skeletal Fluorosis Causes Bones to be Brittle & Prone to Fracture
It has been known since as the early as the 1930s that patients with skeletal fluorosis have bone that is more brittle and prone to fracture. More recently, however, researchers have found that fluoride can reduce bone strength before the onset of skeletal fluorosis. Included below are some of the
A Second Look at Fluoride Exposure and Hip Fractures
In critiquing the York Review I spent a considerable time reading the literature on Hip Fractures and exposure to fluoride. I thought readers would find it helpful to have an up-to-date list of the studies published since 1990. While the evidence from these human epidemiological studies is mixed, when the issue is
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