2. What happens to fluoride in your body?
All the important intake of fluorine is by mouth. People are exposed to fluorine in several different forms. In particular, the chemicals used to add fluoride to drinking water include hexafluorosilicic acid and hexafluorosilicates. Under normal conditions, however, these release all their fluorine as fluoride ions in solution. People are also be exposed to fluoride from its natural occurrence in drinking water.
Water used for washing may also contain fluoride. There is no data on fluoride absorption through the skin, but the fluoride ion will not readily pass through the skin and this pathway is not likely to contribute to people’s fluoride intake.
There is no proved absorption in the mouth. When swallowed, fluoride is absorbed via the stomach and intestines, and passes rapidly round the body in the bloodstream. Peak blood levels appear in 30-60 minutes after swallowing. The most soluble fluoride compounds, such as sodium fluoride in water, tablets and toothpaste, are almost completely absorbed. The less soluble compounds with calcium, magnesium or aluminium are less well absorbed.
Once in the blood, fluoride is gradually removed via the kidneys, reducing to half its original level in between three and ten hours. The long-term blood level is influenced by daily exposure as well as by take-up in growing bone and release as old bone is broken down. Children clear fluoride about as rapidly as adults.