Oct. 10, 2000 -- Drinking bottled water may be trendy, but a new study shows that, despite its taste, the stuff straight from the tap may be better for your bones. Researchers found that drinking fluoridated tap water slightly improved bone density in women and reduced their risk of hip and spine fractures.
But the study did find an increase in wrist fractures among women who drank fluoridated water -- a fact that seriously concerns one fluoridation expert.
The study focused on more than 7,000 Midwestern women -- all at least 65 years old -- and found that "community water fluoridation slightly decreased risk of fractures at both hip and spine in older white women," says study author Kathy Phipps, PhD, an epidemiologist, bone and mineral expert, and associate professor at Oregon Health Sciences University. "This is the first comprehensive study of this issue," says Phipps, whose study was published in the British Medical Journal.
Controversy has swirled around the fluoride issue since the 1940s, when the mineral was first added to community water supplies across the U.S. as a way to prevent tooth decay. In fact, in Grand Rapids, Mich. -- the city where Phipps conducted her study -- dental decay rates declined by 56% in the 15 years after fluoride was added, she says. "Those benefits have been widely documented," she tells WebMD.
But some other studies have suggested that fluoride increases risk of bone fracture in women.
"Increased risk of fracture has been debated for a very long time," Phipps says. "And it's true that if you have very, very high doses of fluoride, you do fracture more. But at levels in community water supplies -- one part per million -- our study is showing there is no increased risk of fracture. So community water fluoridation is a safe way to prevent cavities and may be slightly beneficial for osteoporosis."
Even many types of bottled water -- with the exception of distilled water -- may contain fluoride, says Phipps: "A lot have fluoride in them; even natural spring water, even water imported from Europe, could have fluoride in it. It may have very low levels, but it has some fluoride."
For her study, Phipps recruited women who lived in four Michigan communities from 1950 to 1994. The researchers looked at each woman's household water supply to determine which women had been exposed continuously to fluoridation, those whose exposure had been mixed over the years, and those with no exposure.
All women received bone-mineral density tests (tests that are commonly used to help diagnose osteoporosis) of the spine and femur, says Phipps. Questionnaires helped establish each woman's fracture risks, asking such questions such as what drugs and supplements they took, how many children they had, whether they were in menopause, and whether they had a history of fractures. The women were also asked about their activity levels.
Phipps found that women with continuous exposure to fluoride had increased bone mass in their spines and upper legs; she also found that the same women had decreasedbone mineral density in their wrists. They also had fewer fractures of the spine, hip, and upper leg, but had more wrist fractures than women with no exposure. The findings for the women with "mixed exposure" to fluoride did not differ from those in women with no exposure.
Time frame is essential in fluoride studies, says Phipps. "The benefits of fluoride are cumulative, and these were women with minimum of 20 years of exposure," she tells WebMD. "It takes a prolonged exposure to see the benefits."
But one expert says he is not convinced that drinking fluoridated water leads to stronger bones.
"I think it would be a wildly optimistic assumption that because fluoride is good for your teeth, it's also good for your bones," long-time fluoride researcher Paul Connett, PhD, tells WebMD. "The numbers of wrist fractures [Phipps] found were not insignificant. These increases in wrist fractures are raising a huge red flag."
Fluoride indeed increases bone mineral density, up to a point -- but high doses makes bones more brittle, says Connett, a professor of environmental chemistry and toxicology at St. Lawrence University in New York. "We know much about the biological mechanisms that make this happen," he says.
So how much fluoridated water you drink does make a difference, says Connett. "Keep in mind that 50% of all the fluoride you ingest is going into your bones. ... It's really a no-brainer. If you want fluoride, brush it on your teeth and spit it out. What you shouldn't be doing is swallowing the stuff. The worst thing people could do is start chugging this stuff and do themselves damage. It's cumulative over your lifetime."
But an editorial published along with Phipps' study says that water fluoridation may be an answer to osteoporosis, a major public health problem. "There seems to be reasonable strong evidence that an optimal amount of fluoride in drinking water -- either added or occurring naturally -- does not increase the risk of osteoporotic fractures in elderly people. ... Fluoride seems to be the only drug capable of increasing ... bone mineral density," writes Hannu W. Hansen, a professor in the Community Dentistry Institute at the University of Oulu in Finland.
Because study results have been conflicting, though, Hansen writes that "the true value of the gain in bone mineral density remains questionable." Conflicting results may be caused by biases in studies, by the need for calcium supplements in addition to fluoride, and by the fact that high fluoride doses may be harmful and low doses beneficial, says Hansen.