Fluoride is a naturally present compound in our environment. It comes from fluorine, a toxic chemical element that exists as a gas in a pale-yellow colour. Since fluorine is highly reactive, it never exists by itself in nature. It reacts with other elements to form minerals with fluoride compounds in rocks and soil [1]. Fluoride is also present in all natural water, as well as in plants and animals [2].

Every day, we consume a small amount of fluoride from our diet since it can be found in trace amounts in almost all food: meat, fish, cereals, tea, wine, beer, cheese, seafoods, etc. Black tea and shellfish products are known to have the highest concentration of fluoride at 2-5 ppm or mg/L [2]. The use of Teflon-coated also leak fluoride into the food prepared. We also take in fluoride from fluoridated water supplied in our tap water system, a public health practice worldwide called water fluoridation. In Singapore, for example, sodium silicofluoride has been added to the treated water since 1957 [3]. Fluoride is also a key ingredient of oral hygiene products such as toothpastes and mouth rinses we use daily.

It seems like we are exposed to fluoride everywhere. Is it safe?

Fluoride the hero

The main reason for water fluoridation and the additional of fluoride into the oral hygiene products is for the prevention of dental caries, i.e. tooth decay. About 50% of the fluoride that is absorbed into the body is quickly bound with hard tissues, including bones and teeth, with the rest being excreted in the urine. Fluoride ingested regularly during tooth development are deposited throughout the entire tooth structure, making the teeth stronger and providing long lasting protection. A continuing supply of fluoride subsequently can be deposited on the surface of the teeth and helps to prevent decay [1].

According to the World Health Organization (WHO), water fluoridation reduces the prevalence of dental caries by 15% and fluoridated oral products reduces dental caries by 24-26%, measuring with the decayed, missing, and filled tooth surfaces (DMFS or dfs) index [4]. There is also strong evidence supporting the use of fluoride supplements in the form of tablets, lozenges, or drops to prevent tooth decays in adults according to a systematic review [5]. Such evidence is often cited to support the public water fluoridation programme and the use of fluoridated oral hygiene products for the control of dental caries in the community [6].

Fluoride the villain

The ingestion of fluoride is not without risk. After all, fluoride is a poison at a high dosage. The current upper limit for fluoride intake is set by WHO at 1.5mg/day [7].

Ingesting a high dosage of 35-70 mg/kg body weight of fluoride can be life-threatening [1]. Symptoms of fluoride poisoning include abdominal pain, diarrhoea, vomiting, excess salivation, and thirst. Immediate medical attention is required for any suspected case of fluoride poisoning. Nonetheless, fluoride poisoning is very rare and mainly due to accidental ingestion of large amount of fluoride content oral products or over-fluoridated water [2].

What is more concerning is the effect of long-term exposure to fluoride higher than the recommended upper limit: at 2 to 8 mg of fluoride daily, a condition called fluorosis may arise [1]. Fluorosis can affect the teeth, bones, and other organs.

Children are especially at risk of dental fluorosis. A study conducted in Singapore more than two decades ago found that more than 35% of the children had moderate to severe dental fluorosis. This can be partly due to the consumption of fluoridated water [8]. Hence, it has been suggested that children should avoid fluoride exposure in their first three to six years to prevent fluorosis from occurring in the most prominent and/or most susceptible teeth [1].

With excess fluoride, enamel of the teeth become mottle (spots) and discoloured, teeth become hard, but brittle, and the tooth’s surface pitted. Excessive fluoride exposure of the skeletal system can lead to the initial symptoms of diffuse aches, muscle weakness, chronic fatigue and stiffness of joints. Osteoporosis can develop. Weak bones and joints render movement becomes difficult and painful [7]. Over exposure to fluoride can also lead to hypothyroidism and insulin resistance, increasing the risk of diabetes, obesity, and cardiovascular diseases [7]. There are also studies that link excessive fluoride exposure to the bone, bladder, and uterine cancers [9-11].

Recently, there is also a debate in the scientific community on whether fluoride is a neurotoxin that can severely impact brain development of the children. The debate started with the publication of a systematic review and meta-analysis of 27 population-based studies that found children in high-fluoride areas had significantly lower IQ scores than those who lived in low-fluoride areas [12]. This finding makes fluoride to be classified as a developmental neurotoxicants alongside other toxins including lead, methylmercury, polychlorinated biphenyls, arsenic, and toluene [13]. Such classification received much objection from the dental establishment which strongly advocates the use of fluoride for caries prevention [14].

Water fluoridation: is it necessary?

With the potential adverse effect of excessive fluoride exposure to human health, many have questioned the need to continue water fluoridation programme as a public health policy. It has already been established that topical application of fluoride on teeth is far more effective in preventing dental caries than water fluoridation [15]. It is also hard to limit exposure to fluoride with the pervasiveness of water fluoridation. Ingestion of fluoride way above the upper limit has been frequently reported in many studies throughout the world [15]. Furthermore, from the ethical standpoint, water fluoridation represents a force medication without the patients’ informed consent, which is against medical ethic [16].

Nonetheless, as reported by the European Scientific Committee on Health and Environmental Risks,   water fluoridation remains the only caries preventive measure that can reach disadvantaged children from the lower socioeconomic groups [17]. Until more cost-effective and pervasive mean can be found, water fluoridation cannot be easily replaced. This is one of the most important reasons supporting the continuation of water fluoridation, even in affluent countries such as Singapore [6].

Limiting fluoride exposure

For anyone who is concerned with excessive fluoride exposure, here are a few ways to minimise daily exposure:

1. Use water filter – Install a home water filtration system that can remove fluoride from tap water for daily consumption.  Most commercial water filtration systems can remove fluoride up to even 100% [18].
2. Use fluoride-free dental products – conscious effect to replace dental products such as toothpaste and mouth rinse with those contain no fluoride.
3. Avoid Teflon-coated cookware – Teflon-coated cookware is known to leak fluoride, so don’t use them to prepare food.
4. Moderate consumption of high fluoride food – This includes processed food, tea (both black and green), wine, seafood and shellfish.
5. Check the ingredient list before you buy – a lot of products may contain added fluoride, even for basic things such as salt and milk. So, learn to read the label.

Conclusion

A small amount of fluoride can help to make strong teeth and bones, but over exposure over a long period of time can become a health hazard. Water fluoridation will remain as a public health practice for the prevention of caries, after balancing the benefits and risks of fluoride. Steps can be taken to avoid and limit exposure for anyone who are concerned with the health risk of fluoride.

References

 

[1]         V. Dhar, M. Bhatnagar, Physiology and toxicity of fluoride., Indian J. Dent. Res. 20 (2009) 350–355. doi:10.4103/0970-9290.57379.

[2]         D. Kanduti, P. Sterbenk, A. Artnik, Fluoride: a Review of Use and Effects on Health, Mater. Socio Medica. 28 (2016) 133. doi:10.5455/msm.2016.28.133-137.

[3]         PUB Water Treatment, (n.d.). https://www.pub.gov.sg/watersupply/watertreatment (accessed May 9, 2017).

[4]         P.E. Petersen, M.A. Lennon, Effective use of fluorides for the prevention of dental caries in the 21st century: the WHO approach, Community Dent. Oral Epidemiol. 32 (2004) 319–321. doi:10.1111/j.1600-0528.2004.00175.x.

[5]         C.M. Vargas, Fluoride supplements prevent caries but can cause mild to moderate fluorosis, J. Evid. Based. Dent. Pract. 11 (2011) 18–20. doi:10.1016/j.jebdp.2010.11.022.

[6]         Benefits of Public Water Fluoridation Well-Documented, (n.d.). https://www.moh.gov.sg/content/moh_web/home/pressRoom/Media_Forums/2015/benefits-of-public-water-fluoridation-well-documented.html (accessed May 9, 2017).

[7]         M.S. Kurdi, Chronic fluorosis: The disease and its anaesthetic implications, Indian J. Aneasthesia. 60 (2016) 157–162. doi:10.4103/00195049.177867.

[8]         G.L. Lo, R.A. Bagramian, Prevalence of dental fluorosis in children in Singapore, Community Dent. Oral Epidemiol. 24 (1996) 25–27. doi:10.1111/j.1600-0528.1996.tb00807.x.

[9]         E.B. Bassin, D. Wypij, R.B. Davis, M.A. Mittleman, Age-specific Fluoride Exposure in Drinking Water and Osteosarcoma (United States), Cancer Causes Control. 17 (2006) 421–428. doi:10.1007/s10552-005-0500-6.

[10]      E. Tohyama, Relationship Between Fluoride Concentration in Drinking Water and Mortality Rate from Uterine Cancer in Okinawa Prefecture, Japan, J. Epidemiol. 6 (1996) 184–191. doi:10.2188/jea.6.184.

[11]      P. Grandjean, J.H. Olsen, Extended Follow-up of Cancer Incidence in Fluoride-Exposed Workers, J. Natl. Cancer Inst. 96 (2004) 802–803. https://www.ncbi.nlm.nih.gov/pubmed/15150310 (accessed May 9, 2017).

[12]      A.L. Choi, G. Sun, Y. Zhang, P. Grandjean, Developmental Fluoride Neurotoxicity: A Systematic Review and Meta-Analysis, Environ. Health Perspect. 120 (2012) 1362–1368. doi:10.1289/ehp.1104912.

[13]      P. Grandjean, P.J. Landrigan, Neurobehavioural effects of developmental toxicity, Lancet Neurol. 13 (2014) 330–338. doi:10.1016/S1474-4422(13)70278-3.

[14]      J. Gelinas, M. Allukian, Neurodevelopmental toxicity: Still more questions than answers, Lancet Neurol. 13 (2014) 647–648. doi:10.1016/S1474-4422(14)70119-X.

[15]      S. Peckham, N. Awofeso, Water fluoridation: A critical review of the physiological effects of ingested fluoride as a public health intervention, Sci. World J. 2014 (2014). doi:10.1155/2014/293019.

[16]      K.K. Cheng, I. Chalmers, T.A. Sheldon, Adding fluoride to water supplies., BMJ. 335 (2007) 699–702. doi:10.1136/bmj.39318.562951.BE.

[17]      U. Ackermann-Liebrich, H. Autrup, D. Bard, P. Calow, S. Canna Michaelidou, J. Davison, W. Dekant, P. de Voogt, A. Gard, H. Greim, A. Hirvonen, C. Janssen, J. Linders, B. Peterlin, J. Tarazona, E. Testai, M. Vighi, Critical review of any new evidence on the hazard profile, health effects, and human exposure to fluoride and the fluoridating agents of drinking water, 2011. doi:10.2772/38897.

[18]      B. Eftekhar, M. Skini, M. Shamohammadi, J. Ghaffaripour, F. Nilchian, The Effectiveness of Home Water Purification Systems on the Amount of Fluoride in Drinking Water,J Dent (Shiraz). 16 (2015) 278–281. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4623834/