By Ken Perrott 09/08/2016

Discussion of fluoridation here concentrates on community water fluoridation. But some countries (parts of Europe, and Latin America, for example) fluoridate their salt instead of their water.  This could be for a number of reasons – the state of the water reticulation system, or political opposition to water fluoridation, etc.

The effectiveness of community water fluoridation in reducing tooth decay is well established by research, but there has been far less research on the effectiveness of salt fluoridation. Evidence suggests the effectiveness of the two fluoridation methods is similar but new research from Latin  America found water fluoridation significantly better than salt fluoridation.

It’s a very good study, large numbers of subjects and good consideration of possible confounders. But the authors themselves suggest their findings are more relevant to developing countries than developed countries with better oral health systems.

The paper, titled Comparative effectiveness of water and salt community-based fluoridation methods in preventing dental caries among schoolchildren , is published in Community Dentistry and Oral Epidemiology.

The researchers used data from survey of the oral health of 1528 twelve-year-olds in Porto Alegro, South Brazil  (water fluoridated) and 1154 twelve-year-olds in Montevideo, Uruguay (salt fluoridated). Diagnostic procedures were standardised and the data adjusted for gender, maternal education, school type, brushing frequency, use of dentifrice, professional fluoride application, access to dental services and consumption of soft drinks.

Caries prevalence and decayed missing and filled teeth (DMFT) were measured using standard WHO procedures, and modified WHO procedures (which also included noncavitated lesions).

The graphs below show the adjusted data for caries prevalence (%) and DMFT.
Caries water vs salt fluoridation

DMFT water vs salt fluoridation

Both caries prevalence and DMFT were significantly higher for children from salt-fluoridated Montevideo than similar children from water-fluoridated Porto Alegro.

Take with a grain of salt

Apparently this is the first study showing a statistically significant difference between water and salt fluoridated areas. Similar studies in Freiberg, Germany and Dublin, Ireland had shown no significant differences. The larger sample sizes of the current study may have contributed to the difference. However, the authors also warn that the different situations may also be a factor.

Developing countries have higher prevalence of caries and poorer access to others sources of fluoride than developed countries. Whereas water fluoridation reaches the whole population fluoridated salt may not have such a regular use. In Uruguay the salt fluoridation programme is limited to salt for domestic use. It does not cover public and private canteens, restaurants and bakeries (which the WHO recommends).

So, an interesting study with a clear result – but one that should not be cherry picked to confirm a bias. It indicates community water fluoridation will probably be more effective than salt fluoridation in developing countries – especially if a salt fluoridation programme is not complete. But this should not be used to argue against a good salt fluoridation programme in developed countries


0 Responses to “Is water fluoridation better than salt fluoridation?”

  • But with reduced salt intake (cf. iodine from iodised salt), the amount of fluoride delivered by salt will be small, not to mention widely varying. Most people drink/use a reasonably similar amount of water per day. Salt, not so much (I have zero data to back this up…).

  • Let’s not switch to salt without first understanding the reason why some have done so. I’m only speculating but would guess that salt is an attractive medium in countries with poor quality water supplies (that’s about 80% of the globe, IMHO).
    My understanding on the reason for choosing water was the high quality of dental care in communities which had naturally occurring fluoride in their water. I guess there could be natural beneficial levels of fluoride in some salt supplies too. But if it’s working well through water, let’s stay with that. Leave salt to those communities where good clean water is not readily available.
    As for iodine, iodine in salt is an emerging issue: I’ve effectively lost my thyroid glands through temporarily living in a country where salt iodine levels were set too low for me . In many countries, if we cut back too much on salt, goitres will be prevalent again.

    • No, I am not advocating for fluoridated salt. Just using this paper as an example of how we always need to check the context and avoid using the results as if they apply everywhere.