All organisms are exposed to fluoride released from natural sources and/or by human activities.
Fluoride can help prevent cavities, but at high intakes it can harm teeth development (dental fluorosis) and at higher intakes still, weaken and deform bones (skeletal fluorosis). There is a narrow range between intakes which are beneficial and those which begin to be detrimental.
When drinking water is artificially fluoridated, the "optimum" level of fluoride, associated with the maximum level of dental caries protection and minimum level of dental fluorosis, is considered to be approximately 1 mg/litre. Although there has been an increase in the prevalence of dental fluorosis over the past 30 to 40 years, it has generally been attributed to the widespread increased intake of fluoride from sources other than drinking water, such as toothpastes, mouth rinses, fluoride supplements, fluoridated salt or milk, as well as locally applied dental gels, solutions and varnishes.
Effects on the bone, such as skeletal fluorosis and fracture, are considered to be the most relevant outcomes in assessing the adverse effects of long-term exposure of humans to fluoride.
In areas of the world with high levels of fluoride naturally present in minerals and water, intake of fluoride from drinking water and foodstuffs is the primary cause for endemic skeletal fluorosis, a crippling disability that affects millions of people in various parts of Africa, China and India. In some regions, the indoor burning of fluoride-rich coal also serves as an important source of fluoride.
At total fluoride intakes of 14 mg/day, there is clear evidence of skeletal fluorosis and an increased risk of bone fractures; at total intake levels above about 6 mg fluoride/day the evidence is suggestive of an increased risk of effects on bone.
There is inadequate information for estimating total exposure to fluoride and the uptake into the body from different sources which limits the conclusions on dose response that can be drawn from studies on adverse effects. Excess exposure to fluoride in a form that can be absorbed by organisms poses a risk to aquatic and terrestrial environments.
There is a need to improve the knowledge available on the accumulation of fluoride in organisms and how this can be monitored and controlled.
The biological effects associated with different levels of fluoride exposure should be better characterised. More...