For a long time, the joke around the town of Naivasha in Nakuru County has been that you can tell locals from visitors by looking at their teeth. The majority of locals in Naivasha have brown teeth that have taken their smile away. These brown teeth have a common denominator: dental fluorosis.

According to the Centre for Disease Control (CDC), dental fluorosis is a condition that causes changes in the appearance of tooth enamel. “Dental fluorosis is caused by taking in too much fluoride over a long period when the teeth are forming under the gums,” the CDC states, adding that moderate and severe forms of dental fluorosis can result in more extensive enamel changes.

“With severe forms of dental fluorosis, pits may form in the teeth. These severe forms mostly occur in communities where the level of fluoride in water is more than 2 milligrams per liter,” the CDC states. Naivasha is not the only community that is affected by dental fluorosis. Areas such as Makindu, and Kibwezi are also affected.

For example, a study that was published by Geosciences, an open-access journal, found that fluoride, among other physiochemical parameters that were analyzed in Makueni and Makindu areas exceeded the permissible drinking water limits set by both the World Health Organization and the Kenya Bureau of Standards (Kebs).

The study, ‘Naturally Occurring Potentially Harmful Elements in Groundwater in Makueni County, Southeastern Kenya: Effects on Drinking Water Quality and Agriculture’, reported on the physiochemical characteristics of 20 drinking water sources including boreholes, shallow wells, streams and tap water that were collected during the dry season of November 2018. It also reviewed the geochemical processes controlling their composition, and their suitability for drinking water and irrigation.

“Consumption of high amounts of fluoride of more than 1.5 mg/L can be detrimental as it can result in several degrees of dental and skeletal fluorosis, depending on the dosage and duration of consumption,” the study report said.

“Signs of dental fluorosis were observed in some members of the local population during sampling, indicating that the area has a fluorosis issue.” Boreholes in the Nairobi metropolitan area and parts of the Rift Valley such as Baringo have also been found to contain high concentrations of fluoride which may discolour your teeth.

How dental fluorosis it affects people

According to the World Health Organization, ingestion of excess fluoride, most commonly in drinking-water, can cause fluorosis which affects the teeth and bones. “Moderate amounts lead to dental effects, but long-term ingestion of large amounts of fluoride can lead to potentially severe skeletal problems,” says the WHO.

The WHO says that the dental effects of fluorosis develop much earlier than the skeletal effects in people who have been exposed to large amounts of fluoride. “Clinical dental fluorosis is characterized by staining and pitting of the teeth. In more severe cases all the enamel may be damaged,” says the WHO. The global health body however adds that fluoride may not be the only cause of dental enamel defects.

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“Enamel opacities similar to dental fluorosis are associated with other conditions, such as malnutrition with deficiency of vitamins D and A or a low protein-energy diet. Ingestion of fluoride after six years of age will not cause dental fluorosis,” states the WHO.

In most cases, the WHO says that although drinking water is the most common source of fluorosis,  people affected by fluorosis could also have been exposed to multiple sources of fluoride such as food, air due to gaseous industrial waste, and excessive use of toothpaste.

“A person’s diet, general state of health as well as the body’s ability to dispose of fluoride all affect how the exposure to fluoride manifests itself,” says the WHO. Waters with high levels of fluoride content are mostly found at the foot of high mountains and in areas where the sea has made geological deposits.

The WHO states that the currently known fluoride belts on land include one that stretches from Syria through Jordan, Egypt, Libya, Algeria, Sudan and Kenya, and another that stretches from Turkey through Iraq, Iran, Afghanistan, India, northern Thailand and China.

Skeletal fluorosis

Skeletal fluorosis is the severe outcome of the ingestion of fluoride. According to the WHO, chronic high-level exposure to fluoride can lead to skeletal fluorosis. “In skeletal fluorosis, fluoride accumulates in the bone progressively over many years. The early symptoms of skeletal fluorosis, include stiffness and pain in the joints,” the WHO states. It adds that in the severe cases, the bone structure may change and ligaments may calcify. This will cause the impairment of muscles and pain.

“Acute high-level exposure to fluoride causes immediate effects of abdominal pain, excessive saliva, nausea and vomiting. Seizures and muscle spasms may also occur,” the WHO says.