What you need to know:
Fluoride is a soluble salt that occurs naturally in groundwater, foods, soil and some minerals.
Locally, it is mostly consumed in water.
Fluoride has no colour, taste or smell and can only be detected in a laboratory.
Do you live in the Nairobi metropolitan area? Were you drawn to your current residence because the developer said county water supply is supplemented by a borehole and hence a reliable supply all year round?
You may want to think twice before drinking that water.
Nairobi’s borehole water, local researchers say, contains high concentrations of fluoride, which may discolour your teeth.
Dr Regina Mutave, a senior lecturer in community and preventive dentistry at the University of Nairobi, says water from about half of the boreholes in the city and its environs may contain high levels of the mineral.
“Research has generally indicated that borehole water in areas near the Great Rift Valley have a high content of salts. Boreholes in Nairobi contain fluoride due to proximity to the Rift Valley,” she said.
Fluoride is a salt dentists love and loathe in equal measure, she said. When used in small amounts, it helps strengthen teeth when they are forming. It is also used in toothpaste and helps fight bacteria that can cause tooth decay.
In larger amounts, however, it can damage the cells that lay down tooth structure, resulting in more porous teeth than is desired and poor resistance to acid attacks. Such teeth, she explains, will pick up stains from all the foods we eat, giving them the characteristic brown-black colour associated with dental fluorosis.
The condition changes the appearance of tooth enamel, and may result when children regularly consume fluoride during the teeth-forming years, about age eight and younger.
There are two types of fluorosis - dental and skeletal - Dr Mutave said. In dental fluorosis, the effects of excess fluoride can be seen on the tooth enamel. In skeletal fluorosis, the bones are affected the most.
Skeletal fluorosis, experts say, is caused by fluoride accumulation that weakens bones and causes pain in the joints.
Another expert, orthopaedic surgeon John Ombati, also warns against ingesting Nairobi’s borehole water.
“Nairobi and Kenya’s Great Rift Valley contain some of the highest naturally occurring levels of fluoride in the world,” he cautions.
“As a result, nearly 20 million Kenyans ingest toxic levels of the mineral and suffer the effects of high fluoride concentrations in their groundwater.”
Drinking water with high levels of fluoride for a long time affects bones, he said, making them weak and brittle due to lack of calcium. This makes people prone to fractures in the upper and lower limb, as well as back and neck pains.
Skeletal fluorosis, Dr Ombati said, affects people with a severe case of fluorosis, and their bones are weak and easy to fracture. Signs of skeletal fluorosis include stiffness and pain in the neck and back and restricted movement and pain in joints, especially knees, hips and shoulders.
Other signs are a totally rigid back and immobility of knees. It can also manifest as deformed bones, which is sometimes seen in newborn babies and children.
A study by the University of Nairobi’s geology department attributed the high levels of fluoride in water to emissions from volcanic activity in the East African Rift system.