Skeletal fluorosis | |
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Specialty | Rheumatology ![]() |
Skeletal fluorosis is a bone disease caused by excessive accumulation of fluoride in the bones. In advanced cases, skeletal fluorosis causes pain and damage to bones and joints.
Common causes of fluorosis include inhalation of fluoride dusts/fumes by workers in industry, use of coal as an indoor fuel source (a common practice in China), consumption of fluoride from drinking water (naturally occurring levels of fluoride in excess of the CDC-recommended safe levels[1]), and consumption of fluoride from drinking tea,[2] particularly brick tea. Skeletal fluorosis can be caused by cryolite (Na3AlF6, sodium hexafluoroaluminate), and the disease was first recognized among workers processing cryolite.[3]
In India, the most common cause of fluorosis is fluoride-laden drinking water which is sourced as groundwater from deep-bore wells. Over half of groundwater sources in India have fluoride above recommended levels.[4]
Fluorosis can also occur as a result of volcanic activity.[5] The 1783 eruption of the Laki volcano in Iceland is estimated to have killed about 22% of the Icelandic population, and 60% of livestock, as a result of fluorosis and sulfur dioxide gases.[6] The 1693 eruption of Hekla also led to fatalities of livestock under similar conditions.[7]
The best way to view the mechanism of action by which fluorine breaks down bones and causes skeletal fluorosis is in a stepwise fashion.
In some areas, skeletal fluorosis is endemic. While fluorosis is most severe and widespread in the two largest countries - India and China - UNICEF estimates that "fluorosis is endemic in at least 25 countries across the globe. The total number of people affected is not known, but a conservative estimate would number in the tens of millions."[10]
In India, 20 states have been identified as endemic areas, with an estimated 60 million people at risk and 6 million people disabled; about 600,000 might develop a neurological disorder as a consequence.[4]
Osteosclerotic phase | Ash concentration (mgF/kg) | Symptoms and signs |
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Normal Bone | 500 to 1,000 | Normal |
Preclinical Phase | 3,500 to 5,500 | Asymptomatic; slight radiographically-detectable increases in bone mass |
Clinical Phase I | 6,000 to 7,000 | Sporadic pain; stiffness of joints; osteosclerosis of pelvis and vertebral spine |
Clinical Phase II | 7,500 to 9,000 | Chronic joint pain; arthritic symptoms; slight calcification of ligaments' increased osteosclerosis and cancellous bones; with/without osteoporosis of long bones |
Phase III: Crippling Fluorosis | 8,400 | Limitation of joint movement; calcification of ligaments of neck vertebral column; crippling deformities of the spine and major joints; muscle wasting; neurological defects/compression of spinal cord |
Symptoms are mainly promoted in the bone structure. Due to a high fluorine concentration in the body, the bone is hardened and thus less elastic, resulting in an increased frequency of fractures. Other symptoms include thickening of the bone structure and accumulation of bone tissue, which both contribute to impaired joint mobility. Ligaments and cartilage can become ossified.[11] Most patients suffering from skeletal fluorosis show side effects from the high fluorine dose such as ruptures of the stomach lining and nausea.[12] Fluorine can also damage the parathyroid glands, leading to hyperparathyroidism, the uncontrolled secretion of parathyroid hormones. These hormones regulate calcium concentration in the body. An elevated parathyroid hormone concentration results in a depletion of calcium in bone structures and thus a higher calcium concentration in the blood. As a result, bone flexibility decreases making the bone more amenable to fractures.[13]
The histological changes which are induced through fluorine on rats resemble those of humans.[14]
As of now, there are no established treatments for skeletal fluorosis patients.[15] However, it is reversible in some cases, depending on the progression of the disease. If fluorine intake is stopped, the fluorine existing in bone structures will deplete and be excreted via urine. However, it is a very slow process to eliminate the fluorine from the body completely. Minimal results are seen in patients. Treatment of side effects is also very difficult. For example, a patient with a bone fracture cannot be treated according to standard procedures, because the bone is very brittle. In this case, recovery will take a very long time and a pristine healing cannot be guaranteed .[16]