A high-level panel has found "no adverse effects" of fluoridation of public water supplies, following a review of scientific evidence.
The just-released review, titled Health Effects of Water Fluoridation: a Review of the Scientific Evidence, was commissioned by the Prime Minister's Chief Science Advisor Sir Peter Gluckman and the Royal Society of New Zealand president Sir David Skegg.
The review looked at the scientific evidence for and against the efficacy and safety of fluoridation of public water supplies, finding the levels used in New Zealand created no health risks and provided protection against tooth decay.
Those councils already adding fluoride to water in New Zealand - amounting to less than half - could be confident about its public health benefits, while those not currently fluoridating water could consider it a safe and effective option, a statement issued on behalf of the panel said.
Sir David described the process for the review as "rigourous", adding it included an extensive evaluation of the scientific literature by a panel of five experts, as well as one lay observer with local body experience.
The resulting report was reviewed by three international experts and by National Poisons Centre director Dr Wayne Temple.
Sir David said the panel paid close attention to the claims that fluoride contributes to the risks of cancer, musculoskeletal and hormonal disorders, as well as to claims that it has adverse effects on brain development - these being the major contentions about potential harms that have been made.
"The panel concluded that the concerns raised by those opposed to fluoridation are not supported by the scientific evidence," he said.
According to the report, the only side effect of fluoridation at the levels used in New Zealand was mild dental fluorosis, which could cause opaque white areas in the tooth enamel that is usually of no cosmetic significance.
This was found to be as common in non-fluoridated areas as it was in fluoridated areas, which was likely a reflection of behaviour such as swallowing of fluoridated toothpaste by young children, the review found.
App users: Tap here for the full report
Sir Peter said the review found "compelling evidence" that fluoridation of the water at the established and recommended levels produced "broad and continuing benefits" for the dental health of New Zealanders.
"The public can be reassured on the basis of robust scientific data, that the implementation of this public health measure poses no risk of adverse health effects," he said.
"It is worth noting that dental health remains a major issue for much of the New Zealand population, particularly in communities of low socioeconomic status."
In a letter to Auckland Council chief planning officer Roger Blakeley, published with the review, Sir David and Sir Peter concluded that the scientific issues raised by those opposed to fluoridation were not supported by the evidence.
"Our assessment suggests that it is appropriate, from the scientific perspective, that fluoridation be expanded to assist those New Zealand communities that currently do not benefit from this public health measure - particularly those with a high prevalence of dental caries."
A forthcoming study from the Ministry of Health was expected to provide further advice on how large a community needs to be before community water fluoridation was cost-effective, with present indications pointing to all communities of more than 1000 people.
The review had been called for by Auckland Council on behalf of several other councils, following a public furore about the use of fluoride in water supplies.
It was part-funded by Local Government New Zealand, Auckland Council and Hutt City Council, contributing $5000 each, to seek a definitive scientific view to inform future local government decision-making.
Last year, the issue became more inflamed when Hamilton City Council voted to remove it from water - a decision that was later reversed when a public referendum found 70 per cent of residents wanted it re-introduced.
Dr Blakely today welcomed the findings, saying it provided guidance for local authorities and "clarity on the benefits of community water fluoridation in New Zealand and around the world".
Dr Blakely also noted that this year's Local Government New Zealand conference recommended that future decisions about fluoridation of water be made by central government, through the Director-General of Health, rather than by local government authorities.
Associate Professor Jonathan Broadbent, of Otago University's Faculty of Dentistry, who has fronted the issue on behalf of the dental community, was overseas and unavailable for comment.
Mary Byrne, national co-ordinator of the Fluoride Action Network NZ, which has been campaigning to remove fluoride from water supplies, had not read the report when approached for comment this morning.
Her group has previously claimed fluoride is harmful and linked to arthritis, cancer, thyroid dysfunction, lowered IQ and hypersensitivity.
Ms Byrne however said she had concerns with the scope of the review, and questioned the panel that lead it: "I would imagine it was just going to be very pro-fluoridation."
"What is the point of reviewing what they already know and centering it on the safety of fluoridation... it just seems like a foregone conclusion".
She also was also concerned that the review did not address the broader philosophical issues that have surrounded fluoridation.
"Philosophically, fluoridation shouldn't happen at all - however, we have major concerns about the safety of fluoridation."
The findings: At a glance
"Artificial" vs "natural" fluoride: "The fluoride-containing compounds used for adjusting fluoride levels in drinking water have been shown to dissolve fully in water to release fluoride ions.
"Evidence for benefits of water fluoridation: Analysis of evidence from a large number of epidemiological studies and thorough systematic reviews has confirmed a beneficial effect of CWF (community water fluoridation) on oral health throughout the lifespan.
"This includes relatively recent studies in the context of the overall reduced burden of caries that has resulted from the widespread use of topical fluoride products."
Known effects of fluoride exposure - dental fluorosis: "Dental fluorosis is a tooth enamel defect characterised by opaque white areas in the enamel, caused by excess exposure to fluoride while the teeth are forming in the jaw and before they erupt into the mouth.
"Most of the dental fluorosis that occurs in this country is very mild, having effects that are only identified by professional dental examination.
"The levels of fluoride used for CWF in New Zealand are relatively low in the range that is known to cause minimal risk for cosmetically problematic fluorosis, as reflected in data from the 2009 New Zealand Oral Health Survey, which showed the overall prevalence of moderate fluorosis to be very low.
"The survey indicated that fluorosis prevalence is not increasing, and that levels of fluorosis are similar between fluoridated and non-fluoridated areas."
Analysis of evidence for adverse effects: "A number of potential adverse effects of the consumption of fluoride had been suggested, though many have only been reported in areas where the natural level of fluoride in water is very high.
The reviewers conclude that on the available evidence there "was no appreciable risk" of cancer and bone fractures - or effects on cognition, reproduction, endocrine function, cardiovascular and renal effects - and effects on the immune system, arising from CWF.
Fluoride exposure in specific population groups
Infants: "Infants 0-6 months of age who are exclusively fed formula reconstituted with fluoridated water will have intakes at or exceeding the upper end of the recommended range.
"The higher intakes may help strengthen the developing teeth against future decay, but are also associated with a slightly increased risk of very mild or mild dental fluorosis.
"This risk is considered to be very low, and recommendations from several authoritative groups support the safety of reconstituting infant formula with fluoridated water."
Young children: "Typical intakes of fluoride from water, food, and beverages in young children in New Zealand are within or below the recommended levels.
"However, intake of fluoride from toothpaste contributes a significant proportion of total ingested fluoride in this group.
"Consumption of fluoridated water is highly recommended for young children, as is the use of fluoride toothpaste, but only a smear of toothpaste should be used..."
Children and adolescents: "This group is not considered at high risk of exposure to excess fluoride, and consumption of fluoridated water and use of fluoride toothpaste are both recommended."
Pregnant women: "Pregnant women are not themselves any more vulnerable to the effects of fluoride than their non-pregnant counterparts, but they may have concerns about fluoride ingestion and its possible effects on their unborn fetus.
"However, no studies to date have found any evidence of reproductive toxicity attributable to fluoride at or around levels used for CWF."
Adults and elderly: "Although most studies of the effects of CWF have focused on benefits in children, caries experience continues to accumulate with age, and CWF has also been found to help reduce the extent and severity of dental decay in adults, particularly with prolonged exposure.
Those with kidney disease: "Because the kidney is the major route of fluoride excretion, blood fluoride concentrations are typically elevated in patients with end-stage kidney disease, and this group may be considered to be at increased risk of excess fluoride exposure. However, to date no adverse effects of CWF exposure in people with impaired kidney function have been documented."
Fluoride in New Zealand
Uses fluoride: Auckland, Wellington, Hamilton, Masterton, Lower Hutt, Upper Hutt, Taupo, Gisborne, Palmerston North, Dunedin, Invercargill, Thames-Coromandel, Waikato, South Waikato, Stratford, Porirua, Manawatu, Ashburton, Clutha and South Taranaki and Kapiti.
Don't use it: Christchurch, Whangarei, New Plymouth, Tauranga, Rotorua, Napier, Wanganui, Nelson, Timaru, Greymouth, Far North, Kaipara, Hauraki, Matamata, Waipa, Western Bay of Plenty, Otorohanga, Waitomo, Ruapehu, Opotiki, Wairoa, Central Hawke's Bay, Tararua, Horowhenua, South Wairarapa, Carterton, Rangitikei, Kawerau, Mackenzie, Waimate, Waitaki, Queenstown, Central Otago, Gore, Southland, Tasman, Marlborough, Kaikoura, Buller, Grey, Hurunui, Waimakariri, Selwyn, Westland.
• The Ministry of Health reccomends that water supplies receive between 0.7 and one milligram of flouride per litre.
• The Institute of Environment Science found in 1999 that with flouridation each case of decay would cost $4.20 to treat and $120 per case without.
• A Herald-DigiPoll survey last year showed 48 per cent of New Zealanders support the addition of fluoride and 25 per cent oppose it. A further 48 per cent believe the issue should be left to councillors to decide.