Can you get too much fluoride from water, toothpaste?

There’s fluoride in my toothpaste why do I need it in my water? Katie Townshend writes.

Before your baby’s first tooth even appears the nurse might hand you a teeny toothbrush and a tube of toothpaste with fluoride in it.

This moment marks the start of a child’s lifelong teeth-brushing journey – one made all the more important for those who live in a region where the water isn’t fluoridated.

But why, when we’re following health advice to brush twice daily with fluoride toothpaste, do we need fluoride in our water?

The issue again made headlines when Dr Ashley Bloomfield departed the Ministry of Health in July. One of his last acts as directorgeneral of health was an order for 14 councils to start fluoridating drinking water – a move that means 60% of the population will have fluoridated water. The order follows a 2021 law change, removing the responsibility from local authorities.

Fluoride is a naturally occurring mineral that’s already in our water and food. It’s good for teeth because it strengthens the enamel to protect teeth from decay, and when minor damage does occur, it helps teeth heal.

The combination of brushing with fluoride toothpaste and having it in the water supply means there is a constant low-level of fluoride in saliva helping to protect teeth from damage caused by things like sugar.

But, the amount of fluoride naturally occurring in New Zealand water isn’t enough to have a protective effect. That’s where water fluoridation comes in.

There’s naturally about 0.2mg of fluoride per litre of water, so councils increase it to between 0.7mg/l and 1mg/l – the level recommended by the World Health Organisation.

Simply put, we need it in both because not everyone brushes their teeth properly. A 2009 Oral Health Survey found only 43% of Kiwi kids were brushing twice daily with fluoride toothpaste, and only 65.3% of adults. While toothbrushing is up to the individual, water reaches everyone – and people living with fluoridated water have significantly less decay than those in nonfluoridated areas.

New Zealand dental experts say having it in the water allows for a population approach to protecting teeth. And everybody benefits.

In the US the Centres for Disease

Control and Prevention found fluoridated water reduced tooth decay by about 25%, and labelled fluoridated water one of the 10 great public health achievements of the 20th century. But is it possible to get too much? Some groups claim – loudly – that fluoride can cause fluorosis (discolouring of teeth), impact IQs and cause bone fractures and cancer.

This is not going to happen as a result of drinking water in New Zealand – to reach a toxic level an adult man would have to drink more than 1500 cups a day.

There’s no significant link between fluoridated water and cancer, and most of the studies into the impact on IQ come from China – where levels of fluoride are up to 20 times higher than New Zealand, and exposure to other substances, including arsenic, have been ignored.

A World Health Organisation report states that in areas where there have been cases of skeletal fluorosis and bone fractures, people were consuming 14mg a day. To consume 10mg in New Zealand you would need to drink 40 cups.

Reporting disclosure statement: This post was written with expert advice from New Zealand Dental Association spokesman Dr Rob Beaglehole. It was reviewed by The Whole Truth: Te Māramatanga expert panel member Associate Professor Lisa Te Morenga.