May 22, 2017

Science Update is a monthly written series tackling some of the controversial topics in the public and aims to provide the current research behind these subjects. This month Dr Ian Musgrave talks about the fear from the kitchen tap – fluoride.

Addition of fluoride to our water supplies has been a public health success both in Australia and overseas, with people enjoying fewer cavities and fewer lost teeth as a result.

More than just avoiding gappy smiles, this has several health benefits including reduced pain and improved nutrition though being able to chew properly. Fluoridation has been listed as one of the top ten most significant public health achievements of the 20th century by the US Centers for Disease Control.

Yet recently there has been a significant push back against fluoridation. Some minor political parties have made anti-fluoridation part of their health platforms, local councils in Queensland have stopped fluoridation and a celebrity chef has railed against fluoridation, saying it is poisoning us. Why has this happened?

While some arguments revolve around consent to medication, the ultimate argument is that at levels present in water fluoridation schemes, fluoride is a toxin with significant long-term adverse effects on health. However, most of the claims are either fanciful (fluoride is not a mind control agent) or occur at concentrations not relevant to fluoride’s public health usage.

What is fluoride?

Fluorine is a highly reactive, toxic gas. Add an electron to fluorine and you have a negatively charged ion, fluoride. This sounds alarming, but remember that chloride, the ion that forms common table salt and is essential for health, is derived from fluorine’s relative the toxic and corrosive gas chlorine.

Fluoride is found naturally in earth’s crust, and enters the water table by water percolating through rocks containing fluoride. Natural levels for fluoride vary greatly, Australia has rather low levels of fluoride in water (except for some areas in central Australia) while some areas in China have very high levels. Fluoride can also be present in food through absorption of fluoride from water sources. Some teas for example, have high fluoride levels. Fluoride is naturally present in our bodies, mostly in bones and teeth.

How does fluoride work?

Both bones and dental enamel are made of hydroxyapatite, a mineral composed of calcium and phosphorus. Fluorine gets incorporated into this mineral as fluoroapatite, which is more resistant to erosion than hydroxyapatite in dental enamel.

Fluoride and dental health

Studies on populations that lived in naturally high fluoride areas compared to low fluoride areas showed that these people had lower levels of dental decay. Since then, numerous studies have shown that supplementing water supplies with fluoride to levels or around 1 part per million (or one milligram of fluoride per litre of water) significantly reduces holes in teeth and tooth loss. In Australia the most recent studies show that tooth decay is reduced by 26 – 44% in children, teenagers and adults .

In terms of preventing tooth decay (cavities and loss), fluoride in water is more cost-effective than other forms of fluoride application (toothpastes, dental fluoride treatment). It is also more equitable to people on low incomes or with limited access to dental treatment by giving them this protection.

Tooth decay is important beyond mere cosmetic appeal. Tooth decay and tooth loss involves pain and suffering, economic burden and associated health challenges such as poor nutrition from the reduced ability to chew properly. Overall, tooth decay and tooth loss leads to a lower quality of life.

Adverse health effects of fluoride

Fluoride, like all treatments, can have adverse effects. These effects depend on the concentration of fluoride people are exposed to. As you might expect, since fluoride is incorporated into teeth and bones, high exposure to fluoride could affect these tissues. Moderately high drinking water exposure to fluoride can cause dental fluorosis, a mottling of the teeth which is aesthetically unpleasant but has no important health effects. Higher levels are associated with skeletal fluorosis, which can have arthritis like effects. However, outside of countries with high levels of environmental fluoride, well above the levels in Australian drinking water, skeletal fluorosis is rare. There have been rare reports of skeletal fluorosis in people who drink excessive amounts of tea i.e the equivalent of 100 teabags a day.

In Australia, the levels of fluoride added to drinking water is between 0.6 – 1.1 milligrams per litre. Lower levels are used in the hotter parts of Australia due to increased water consumption. Countries with high levels of fluoride often have levels between 2 – 10 milligrams per litre fluoride or even higher. In contrast, to poison yourself with fluoride at Australian drinking water levels, you would need to drink 3000 litres of water in one go.

The levels of fluoride in Australian drinking water is such that it gives good dental protection with minimal dental fluorosis.

Other health effects

The pushback on fluoridation comes from claims with either no, or misunderstood, evidence.

The most recent and high profile claim that has been making the rounds is that fluoride is a neurotoxin. This is based on a 2012 study looking at extreme levels of fluoride exposure. Of relevance to the water fluoridation debate, the paper found that children with exposure to high levels of fluoride in drinking water had an average fall of 6 IQ points. There are a number of problems with this study that make the connection between this marginally lower IQ and fluoride tenuous. Most importantly, the levels of fluoride in drinking water in the reference group, i.e. the children the high exposure groups were compared to, were the levels found Australian drinking water with added fluoride. The high exposure groups ranged from around 3 – 12 milligrams per litre, well above Australian exposure levels and most above maximum permissible levels in Australian drinking water.

There have been several systematic reviews of fluoride and health effects in recent years, the two most important for us are the 2007 and 2014 reviews by the Australian National Health and Medical Research Council. Aside from reaffirming the importance of water fluoridation, these reviews found no evidence of health effects outside of dental fluorosis at the concentrations in Australian drinking water (including accounting for fluoride in toothpaste and other sources. Importantly, the 2014 review specifically examined the neurotoxicity of fluoride and found no significant association between fluoride exposure and IQ.

Take home message

Multiple studies have shown that water fluoridation is safe and effective at preventing tooth decay and loss. Claims to the contrary either misunderstand or misrepresent the studies.

This article was originally posted on Australia’s Science Channel.