Fluorosis in adults

• effects of chronic fluoride ingestion in adults
  • features of chronic fluoride toxicity include gastrointestinal effects (dyspepsia, nausea, diarrhoea and vomiting) and skeletal fluorosis characterised by skeletal abnormalities and joint pain, osteosclerosis (abnormal hardening of bone) and exostoses (bony outgrowths) of long bones, vertebra and jaws (1)
    
    
  • fluoride is deposited irregularly in bones and bone can be laid down along muscle attachments and tendons
    
    
  • histologically, skeletal fluorosis is similar to osteomalacia (poor or delayed mineralisation in cortical and spongy bone) but with normal plasma calcium and phosphate levels. The strength of fluorotic bone is poor and spontaneous fractures are common
    
    
  • chronic fluoride toxicity is related directly to the extent and duration of fluoride exposure - however, crippling skeletal fluorosis is extremely rare in the UK and other developed countries
    
    
  • chronic toxicity from fluoride ingestion has been reported in association with ingestion by cryolite (compound of aluminium fluoride and sodium fluoride) workers and in geographical areas which are hot, dry and have extremely high levels of fluoride present in the water
    • there is no evidence of clinical skeletal fluorosis arising from exposures to water supplies in the UK (2)

Summary (1):

• chronic toxicity from fluoride ingestion is rare in the UK and other developed countries - the principal sources of potentially excessive fluoride intake are drinking water, in areas where levels are naturally high, and toothpaste ingestion
• US guidance suggests that the tolerable upper limit for fluoride ingestion is 10mg per day in adults and children older than 8 years
• most public water supplies in the UK contain less than 0.7mg/L fluoride; 10% of supplies are fluoridated to a level of 1mg/L
• standard over-the-counter adult toothpastes contain between 1,000ppmF and 1,500ppmF. High-strength fluoride toothpaste containing either 2,800ppmF or 5,000ppmF is available on prescription in the UK
• a 70kg adult, who does not expectorate after brushing, could ingest a total of 10mg fluoride by swallowing 2g of a 5,000ppmF toothpaste, assuming a fluoride-free water supply, or 1.7g of a 5,000ppmF toothpaste plus 1.5L water containing 1ppmF
• caution is required if high-strength fluoride toothpastes are used in people who may swallow rather than expectorate after toothbrushing.

Notes:

• In the UK there is no maximum recommended daily amount of fluoride (1)
  • however, in the US the recommended tolerable upper limit for fluoride is 10mg daily for adults and children older than 8 years ( a 70kg man drinking 1.5L daily of water containing 1mg/L (1ppmF) fluoride would ingest approximately 1.5mg fluoride each day)

Reference:

• UK Medicines Information (UKMi) pharmacists for NHS healthcare professionals (January 2019). Fluoride toothpaste - what are the dangers of chronic ingestion in adults?
• Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment. COT Statement on Fluorine in the 1997 total diet study. COT statement 2003/03, September 2003.