How Much Fluoride is Too Much?
What is still not clearly established is whether fluoridated water, consumed over a lifetime, may lead to at least the initial stages of skeletal fluorosis. A threshold intake amount of 10 milligrams (mg) fluoride per day for an adult for a decade or two has been suggested as necessary before skeletal fluorosis is likely to result. Do Americans get this much fluoride? No sufficiently large study has ever been conducted in the US to determine the total intake of fluoride. However, a recent British study looked at a biomarker for fluoride intake, which is the amount of fluoride excreted over 24 hours in urine. It found that several percent of adults were likely already exceeding an intake of 10 mg/day.
The situation may actually be far worse in the US, since in Britain, only 10 percent of the population has fluoridated water, whereas in the US over 65 percent does. Fluoridated water was an important contributor to the high fluoride intake among some individuals in the British study.
Skeletal fluorosis was identified in a 2006 report by the National Research Council (NRC) as an adverse effect that needed to be considered by the EPA in establishing maximum safe levels of fluoride in drinking water. But so far, the EPA has done no serious analysis of the potential for skeletal fluorosis in the US.
How Fluoride Damages Your Bones
The NRC report had even more concern for another effect of fluoride on bone, which is the decrease in bone strength that can result in higher risks of fractures, especially in the elderly. This effect has not been as well studied as skeletal fluorosis, but since fractures of the hip in the elderly are such a serious health problem, often sending patients into a spiral of declining health ending in death, it is crucial to know whether water fluoridation is contributing to decreased bone strength. Some basic information about how fluoride acts in your body is helpful to understanding its health effects.
First, about half of the fluoride you consume is excreted through your kidneys into your urine, while the other half becomes bound in your skeleton. The fluoride that enters your bones is eliminated very slowly. The NRC estimates the biological half-life of fluoride in bone (the time for half of it to be removed) is as long as 20 years.
Unfortunately, most people—especially if you're drinking fluoridated water on a daily basis—have constant low level exposures to fluoride, they are taking more fluoride into their bones than what is being removed, so the level of fluoride in their bones increase steadily over time.
Young people generally don't have more than a few hundred parts per million (ppm) of fluoride in their bones, whereas older people living in fluoridated areas can have several thousand ppm, which is the level where skeletal fluorosis begins. Fluoride excretion in urine is reduced in those with decreased kidney function, which is also very common in older people. So, the elderly not only have accumulated higher levels, but they are losing the ability to effectively remove it as well.
An analogy can be made between fluoride accumulating in bone and persistent chemicals such as dioxin or PCBs, which often accumulate, because they also have long biological half-lives in human tissues.
Your bone is constantly being "turned over" in a process called remodeling. The mineral portion of your bone is broken down by one type of cell and then rebuilt by another. Fluoride appears to interfere with this essential process. The result is excessive mineralization and enlargement of your bones, and a disruption of the precise architecture needed to maintain resistance to fracture.
Ironically, while fluoride often does increase your bone mineral density, which is a commonly used measure of bone quality, it simultaneously makes your dense bone more brittle and therefore more subject to fracture. Remember thicker bone does NOT equate to stronger bone…