As the first stop along the digestive tract when we eat, the mouth plays several vital roles in initiating digestion. Our oral health is also closely linked to nutrition — a relationship that is exemplified through the known roles of sugar and acidic foods and liquids in increasing the risk of dental caries (or decay), vitamin C in promoting gum health and healing and fluoride in promoting tooth formation and preventing caries. Excessive fluoride exposure can be a cause for concern, though—particularly since most Americans are exposed to it through our dietary intake and in dental products. Since we are exposed to fluoride through our daily diets, how can we be careful to maintain a safe and beneficial exposure level?
What functions does fluoride play in the body?
Fluoride is an electrically charged (or ionic) form of the naturally occurring element known as fluorine. It helps with the structural stability of teeth and bones through interactions with calcium phosphates, molecules in our bones made of calcium, phosphorus and oxygen. Fluoride occurs naturally in the body in the form of calcium fluoride, which is primarily found in the bones and teeth. In the mouth, fluoride can inhibit bacteria that ferment sugars and produce acid, thereby preventing decay. It also helps to adhere calcium and phosphorus to enamel to promote remineralization, which is the process through which tooth enamel is rebuilt after it begins to decay. Through these processes, fluoride can help to prevent and even reverse tooth decay — particularly when applied topically.
Elsewhere in the body, it stimulates the proliferation of osteoblasts (or bone-building cells), making it an important element for bone growth in children.
Where do we get fluoride in the diet?
Fluoride is naturally found in the soil and is taken up by many types of plants. As a result, foods derived from those plants, as well as meat and dairy from animals that eat those plants, contain trace amounts of fluoride. However, most of the fluoride we consume comes from fluoridated water, foods and beverages made with fluoridated water, and dental products (like toothpaste) that contain fluoride.
Tea actually provides more fluoride than fluoridated water because tea leaves come from the Camellia sinensis plant, which also takes up some fluoride from the soil. All other foods and beverages are estimated to provide less than 1 mg of fluoride per serving. Examples of foods and drinks that contain measurable amounts of fluoride are shown below. Note that the beverages and grains listed are made with fluoridated water; versions with unfluoridated water would be much lower (and precise concentrations could vary widely). Some medications and multivitamins also contain fluoride.
Since 1945, most community water systems in the US have added fluoride to water as a public health measure to reduce the incidence of dental caries. While the US Public Health Service reduced its recommended fluoride concentrations from 0.7–1.2 parts per million (ppm) to 0.7 ppm in 2015, variation across systems still exists.
Notably, about 15% of American households get their drinking water from non-fluoridated wells. Also, some varieties of bottled water are made with fluoridated water, but it is impossible to tell based on the brand or label.
How much fluoride do people need to consume?
Adequate Intakes (AIs) for fluoride are based on levels estimated to maximize reductions in the incidence of dental caries without unwanted side effects. One of the primary side effects of too much fluoride is fluorosis, which refers to weakened bones and tooth damage that may appear as discoloration in tooth enamel. Our fluoride needs increase throughout childhood and stabilize once we hit adulthood. It's estimated that our bodies absorb more than 80% of the fluoride we ingest; of that amount, about 50% is retained, and the rest is excreted in the urine. Young children are estimated to retain more — up to 80% — of absorbed fluoride because their rapidly growing bones and teeth take up more of it. AIs and related considerations for safe intake are shown in the table below.
What are the risks and benefits of augmenting fluoride in the water supply?
The fluoride concentration in treated drinking water supplies is typically (but not always) controlled to be approximately 0.7 ppm, as the US Public Health Service recommends. The decision to fluoridate water was informed by epidemiological studies showing that people who lived where drinking water supplies had naturally occurring fluoride levels of at least 1.0 ppm had fewer dental caries than those who lived where fluoride levels were lower. Water fluoridation is intended to prevent tooth decay by providing frequent and consistent contact with low fluoride levels. Fluoridation has been widely accepted as the most practical and cost-effective method of delivering fluoride to all community members since everyone needs to use and drink water.
There is disagreement, however, about the safety of fluoride and the necessity for fluoridation. Some groups (such as the Environmental Working Group) call for lowering the level of fluoride based on concerns about its potential risks, including:
Fluorosis may develop when exposed to too much fluoride in the first eight years of life.
Drinking water is an inexact delivery route because people consume widely different amounts from the tap and have varying exposures through other media.
Accidental overexposure can lead to side effects such as nausea, vomiting, joint pain and skeletal fluorosis (or bone loss).
Some studies in laboratory animals have suggested that high fluoride exposure may be neurotoxic; further, observational studies have found associations between exposure and impaired learning, memory and cognition.
While community-level fluoridation became widely popular in the latter half of the 20th century, many organizations and agencies have adjusted their stance over the past decade. A 2015 Cochrane report, for example, found a dearth of quality research into the effectiveness of water fluoridation for preventing caries in adults. The report noted that dental caries have decreased equivalently in countries without water fluoridation, and they concluded that fluoridation is an unnecessary process.
However, overall, the current body of evidence is insufficient to show causal relationships between the above observations. Most studies suggesting harm also focused on populations with exposures higher than those typically found in community-fluoridated water. Thus, most health professionals and public health associations continue to support routine fluoridation at the level currently deemed safe, along with following advised practices for fluoride-containing dental products.
How can I make sure I'm consuming an appropriate amount of fluoride in my diet?
Given these universal and often unavoidable means of exposure, it's essential to understand how — and how much — fluoride is entering your body. Consider reviewing the following sources of information:
Most states participate in the My Water's Fluoride tool from the Centers for Disease Control and Prevention, enabling residents of those states to learn if their counties routinely fluoridate water and at what approximate concentration. You can also visit the Environmental Working Group's Tap Water Database to learn about utilities with the highest amounts of fluoride and other related details.
To learn the precise level of fluoride in your water, you can take samples to a state-licensed testing lab (found by searching the EPA's Water Lab Network). You can also detect fluoride using home reactive testing kits or strips, which can be purchased at some home improvement stores or online (though the validity of their measurements is questionable). You can read more about testing kits reviewed by Consumer Reports or Good Housekeeping to make an informed decision. If you're concerned about high fluoride levels in your water, reverse osmosis systems, distillation units and certain water filters (but not carbon-charcoal filters) can remove significant amounts.
Talk with your dentist if you're concerned about over- or under-exposure for either a child or an adult. Consider meeting with a dietitian for guidance about incorporating or removing foods and liquids that contain fluoride from your diet, based on your goals. Finally, you can talk with your physician about any possible fluoride content in prescription medications you may be taking.
Resources
Please visit here for a list of resources.
Christina Badaracco, MPH, RD
Christina is a registered dietitian and author who aims to improve access to healthy and sustainable food and educate Americans about the connections between food and health. She loves to experiment with healthy recipes in the kitchen and share her creations to inspire others to cook.
Christina completed her dietetic internship at Massachusetts General Hospital and earned her Master of Public Health degree from the University of California, Berkeley. Previously, she graduated with a degree in Ecology and Evolutionary Biology from Princeton University, after conducting her thesis on sustainable agriculture and energy in Kenya. She has done clinical nutrition research at the National Institutes of Health, menu planning and nutrition education at the Oakland Unified School District and communications at the Environmental Protection Agency's Office of Water. She has also enjoyed contributing to children’s gardens, farmers markets and a number of organic farms.