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To date, the dominant narrative has been that water fluoridation is safe and effective, with advocates claiming strong scientific support and the endorsement of the practice by major dental and public health bodies as evidence of its effectiveness [ 10 ]. This is despite key questions about the efficacy and effectiveness of ingested fluoride, concerns about safety, and questions about ethics and legality producing a debate that is a potent mixture of scientific, professional, corporate, and ethical arguments [ 11 — 14 ].
This paper provides a reasoned assessment on the magnitude of the main positive impact of fluoride ingestion on human health i. In particular, it raises questions about what an acceptable safety margin should be for ingested fluoride and questions why normal rules of safety normally applied to assessments of harm and benefit are not applied to water fluoridation. We examine the key arguments and evidence relating to three areas of current debate—efficacy and effectiveness, adverse impacts on health, and ethics.Bones - Temporada final - Fox Life
The paper concludes that given the questionable evidence of benefit and increasing evidence of harm the policy of water fluoridation for the prevention of dental caries should be abandoned in favour of more effective interventions combining communitywide and targeted oral health interventions.
Efficacy and Effectiveness The only demonstrated positive impact of fluoride on human health is its contribution to prevention of dental caries infection of teeth enamel. Hydroxyapatite in teeth enamel is made up of calcium, magnesium, and phosphate compounds and is susceptible to decay induced by acid-producing bacteria.
Fluoride interacts with hydroxyapatite to form fluoroapatite, which is less susceptible to erosion by acid-producing oral bacteria.
Most of the ingested fluorides reach the teeth via saliva, whose fluoride content varies from less than 0. Fluoride absorption in bones and teeth decreases with increasing age [ 15 ]. It is widely accepted that fluoride only helps prevent dental decay by topical means—by direct action on the tooth enamel predominantly after eruption and dental plaque [ 1617 ].
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Fluoride has also been shown to inhibit cariogenic bacteria. This is postulated to occur mainly through inhibition of enzyme-mediated glycolysis in cariogenic microorganisms such as Streptococcus mutans.
Fluoride is thought to adversely affect polysaccharide metabolism in bacterial cells, reduce the ability of such cells to maintain pH homeostasis, and inhibit encholase as well as other ATPase enzyme systems [ 2021 ]. Salivary secretions help neutralise caries causing acids and facilitate teeth remineralisation. Individuals with low salivary secretions have higher risk of dental caries [ 22 ].
Acid producing normal flora of the oral cavity such as Lactobacillus acidophilus thrive and may become cariogenic in the presence of high sugar intake and fermentable carbohydrates on the enamel, as from carbonated drinks. Thus, the multiple pathways to the development of dental caries make it difficult to accurately ascertain the contribution of fluoride ingestion to dental caries prevention.
Given that the action of fluoride on dental caries prevention is topical, only topical fluoride products are likely to provide optimal benefits claimed for this chemical.
While early studies of water fluoridation suggested substantial benefits in terms of reduced levels of dental caries, these results have always been contested. Early support was based on an assumed systemic role of fluoride in reducing decay [ 34 ]. A number of recent studies have questioned whether water fluoridation is effective with studies suggesting no difference in the level of dental caries between children who drink fluoridated water as compared to those who drink nonfluoridated water [ 26 ].
Despite this community water fluoridation is endorsed by the World Health Authority, the US Public Health Agency, and most dental and public health organisations as a safe and effective method of reducing dental decay i.
This lower observation of the contemporary impact of artificial water fluoridation on dental caries was based on a meta-analysis of water fluoridation studies undertaken prior to the late s by the UK NHS Centre for Reviews and Dissemination [ 28 ] which found that, for children living in areas where water is artificially fluoridated, the change in the prevalence of dental caries was an average increase of However, a recent European review recently concluded that water fluoridation is a crude and rather ineffective form of systemic fluoride treatment to prevent dental caries without a detectable threshold for dental and bone damage [ 30 ].
The findings in the York Review [ 28 ] that children in fluoridated regions had an average of A survey of 55 reputable oral health specialists on the impacts of artificial water fluoridation and other preventive technologies on the decline in dental caries prevalence over the past four decades in most nations revealed that, apart from fluoridated toothpaste, there were conflicting responses on the impact of artificial water fluoridation and other fluoride-based technologies [ 32 ].
Studies focused on dental caries trends following cessation of fluoridation have produced contradictory results, in part due to study technique, availability of other fluoride sources, and consumption patterns of cariogenic foods [ 3334 ]. Adverse Impacts of Fluoride Ingestion on Human Health The classification of fluoride as a pollutant rather than as a nutrient or medicine is a useful starting point for analysing the adverse effect of fluoride.
No fluoride deficiency disease has ever been documented for humans. Indeed, the basis for setting an "adequate intake" of fluoride rests on the alleged ability of ingested fluoride to prevent tooth decay. In their recent review of water fluoridation, the EU European Union Scientific Committee on Health and Environmental Risks highlight that young children are likely to exceed the upper tolerable limits for fluoride consumption in areas with water fluoridation greater than 0.
Their conclusion supports earlier research that suggested that the term optimal fluoride intake should be dropped from common usage [ 39 ]. This study used nonfluoridated water but supports earlier findings by Koblar et al.
The main source of ingested fluoride to teeth is saliva, whose fluoride concentration is much lower than ingested fluoride. Furthermore, dental caries is essentially the outcome of bacterial infections modulated by physical, biological, environmental, behavioural, and lifestyle-related factors such as high numbers of cariogenic bacteria, inadequate salivary flow, high intake of fermentable carbohydrates, inadequate access to dental services, poor oral hygiene, inappropriate methods of feeding infants, malnutrition especially calcium and magnesium deficiencyand poverty.
Fluoride exposure has a complex relationship in relation to dental caries and may increase dental caries risk in malnourished children due to calcium depletion and enamel hypoplasia, while offering modest caries prevention in otherwise well-nourished children.
It has been demonstrated that at low friction loads, enamel hydroxyapatite and fluoroapatite appear to wear in the same way.
However, at high friction loads, fluoroapatite enamel flakes and wears catastrophically, leaving severely fractured enamel, whereas hydroxyapetite enamel does not as it is more adaptable to remodelling. The adverse impact of fluoride in producing brittle teeth has been recognised in laboratory animals sinceand fluoride-induced brittle teeth were demonstrated to be worse with industrial fluorides such as sodium fluoride compared with naturally occurring calcium fluoride [ 47 ].
Sauerheber has analysed the physiologic conditions such as calcium and pH levels and systemic effects of ingested fluoride as well as the efficacy of ingested artificially fluoridated water on dental caries prevention [ 48 ].
He highlights the important distinction that should be made between naturally occurring fluoride calcium fluoride CaF2 found in water supplies and added fluoride compounds sodium fluoride NaF and fluorosilicic acid H2SiF6.
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His analysis is based on a detailed review of the effect of fluorides on physiological functions and concludes that there are harmful effects from adding artificial fluoride compounds to water supplies. He observes that most analyses of fluoridation rarely focus on detailed physiological analysis but rely on observational epidemiological data to demonstrate effectiveness which are rarely sensitive enough or examine potential issues of harm.
One key exception to this was the review by the National Research Council in the USA for the Environmental Protection Agency which took a weight of evidence approach to examining toxicological and physiological effects of fluoride on water [ 49 ].
This review identified a number of potential and established adverse effects including cognitive impairment, hypothyroidism, dental and skeletal fluorosis, enzyme and electrolyte derangement, and cancer [ 49 ]. In a meta-analysis of 27 mostly China-based studies on fluoride and neurotoxicity, researchers from Harvard School of Public Health and China Medical University in Shenyang found strong indications that fluoride may adversely affect cognitive development in children [ 50 ].
All but one study suggested that high fluoride content in water may negatively affect cognitive development. The average loss in intelligence quotient IQ was reported as a standardized weighted mean difference of 0. A particular concern of the NRC committee was the impact of ingested fluoride on the thyroid gland [ 49 ].
They found borderline low FT3 levels among all children exposed to fluoridated water [ 51 ]. The mechanisms through which fluoride exacerbates hypothyroidism include competitive binding with iodine, as well as synthesis obstruction of T3 and T4.
Thus, fluoride-induced hypothyroidism is likely to be more common in iodine-deficient settings. Australian surveys indicate that the general Australian population is mildly deficient in iodine [ 53 ] Iodine-deficient children ingesting fluoridated water have been found to demonstrate intellectual deficits even at water fluoride levels of 0.
The most obvious and widespread impact of fluoride is dental fluorosis. In some cases—where fluoride levels are very high or where there is prolonged ingestion at 2 ppm or higher, cases of skeletal fluorosis have been reported. Skeletal fluorosis is a chronic metabolic bone disease caused by ingestion or inhalation of large amounts of fluoride.
Vertebral osteosclerosis may result in spinal cord compression [ 55 ]. In addition, an increase in bone mass due to fluoride ingestion or treatment for osteoporosis does not translate into improved bone strength, and high doses of sodium fluoride for osteoporosis treatment may increase the risk of vertebral fractures [ 56 ].
Dental fluorosis mirrors skeletal fluorosis. Similar to counterintuitive histological changes in bone, the macroscopic appearance of increasing degrees of dental fluorosis was directly correlated to the degree of subsurface porosity [ 57 ].
Despite such histological changes suggesting that tooth decay prevalence may be higher among children with fluorosis, research findings have been mixed [ 5859 ]. There is no safe limit for fluoride ingestion in relation to dental fluorosis, but fluoridated levels exceeding 0. With these higher levels of fluoride intake, dental fluorosis and other toxic effects noted above have also increased.
Fluoride is a known enzyme disruptor. There are 66 enzymes which are affected by fluoride ingestion, including P oxidases, as well the enzyme which facilitates the formation of flexible enamel [ 65 ]. A recent study of the effects of inorganic fluoride compounds on human cellular functions revealed that fluoride can interact with a wide range of enzyme-mediated cellular processes and genes modulated by fluoride including those related to the stress response, metabolic enzymes, the cell cycle, cell-cell communications, and signal transduction [ 66 ].
Due to high negativity of fluoride, it interacts actively with positively charged ions such as calcium and magnesium. In industrial settings, hydrofluoric acid poisoning is usually treated with intravenous calcium gluconate as such poisoning is associated with acute hypocalcaemia [ 67 ]. As with calcium, magnesium plays important roles in optimal bone and teeth formation.
By competing with magnesium and calcium in teeth and bones, fluoride deranges the delicate bone formation and bone resorption processes. Chronic fluoride ingestion is commonly associated with hyperkalaemia and consequent ventricular fibrillation [ 70 ].
There have also been a number of studies that link fluoride and cancer. More than 50 population-based studies which have examined the potential link between water fluoride levels and cancer have been reported in the medical literature. Most of these studies have not found a strong link between chronic fluoride ingestion and cancer. The York, NRC and SCHER reviews came to similar conclusions [ 283049 ] However, population-based-studies strongly suggest that chronic fluoride ingestion is a possible cause of uterine cancer and bladder cancer; there may be a link with osteosarcoma—highlighted as an area where there is evidence of problems requiring further research [ 3072 — 74 ].
Ethical Arguments Given the uncertainties and debates about effectiveness, efficacy, and the potential for harming health, it is not surprising that community water fluoridation raises important ethical questions. However, these are not restricted to issues of benefit and harm. In addition, community water fluoridation provides policy makers with important questions about medication without consent, the removal of individual choice and whether public water supplies are an appropriate delivery mechanism [ 7576 ].
Those in favour of water fluoridation have argued that it is ethical as it reduces inequalities in dental health by giving most benefit to children in lower socioeconomic groups [ 77 ]. However, the evidence for claiming a reduction in inequalities is generally of poor quality and provides only weak support [ 2876 ]. Given that more recent studies question whether there is any beneficial impact clearly undermines claims that fluoridation is ethical.
Pastoralism occupies a fundamental economic, social and religious role in Andean life. Today, camelid livestock are confined to the ecozone of the puna above 3, maslwhile their presence on the Pacific coast during pre-Hispanic times is attested by archaeological skeletal remains.
This study aims to document herding practices on the northern Peruvian coast during the Early Intermediate Period BC AD by gaining insights into diet, location of breeding and mobility of archaeological camelids from the funerary and ritual contexts of two Mochica sites, Uhle Platform in Huacas de Moche and El Brujo. Archaeological camelids had diverse and complex life histories, usually with substantial maize foddering.
An ontogenetic switch in diet and possible residential mobility during the course of life were identified for some specimens. Our study suggested that Mochica herders adapted their practices to the difficult lowland environment and that herding practices were varied and not restricted to breeding at higher altitudes.
The role of maize in different aspects of the economic life of the Mochicas is also underlined. Introduction Andean pastoralism and the establishment of trade routes between different ecological zones, the so-called concept of Andean verticality, is one of the foundations for the emergence of complex societies in the pre-Hispanic world .
Alpacas Vicugna pacos and llamas Lama glama were domesticated 4,—6, years ago, and experienced an intensification in livestock management from at least the end of the Early Horizon — BC . From then onwards, camelids have occupied a fundamental economic, social and religious role, both in pre-Hispanic and modern Andean cultures . During the pre-Hispanic period, the llama was the only beast of burden and caravans providing goods to different ecological zones were crucial to the development of extensive trade networks  — .
Textiles were manufactured from camelid wool and traded throughout the Andes, their meat was consumed, leather and bones served as raw materials to make tools and various ornaments, and dung was used as fuel. Domestic camelids were sacrificed and deposited into graves to fulfil various symbolic functions  and their entrails could be used to read omens.
Finally, they were a symbol of prestige and a marker of identity . Today, camelid husbandry is essentially restricted to the highlands in an ecozone called the puna that comprises plateaus above 3, masl, and more precisely between 3, and 4, masl .
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Water is supplied by rain, snow and hail during the rainy season. The vegetation comprises wetlands such as bofedales peatlands of the central Andes where Juncaceae species dominate and serve as the primary peat-formers which are naturally conducive to llama and alpaca breeding.
The optimum life conditions for llamas and alpacas vary according to the function the animal serves . Alpaca herds devoted to wool production are raised in rich bofedales pasturelands at higher altitudes than llama herds. The presence of domestic camelids in remote and dramatically different habitats, like the Pacific coast — characterized by a higher mean temperature and higher seasonal variations in temperature than the puna and almost no precipitation — is attested by skeletal remains, textiles and iconography from at least BC onwards  — .
It was formerly assumed that lowland camelids were not raised locally but instead were brought by caravans from the Andes shortly before being butchered or sacrificed . This classical view is challenged by new zooarchaeological studies . The northern coast 0— masl of Peru has witnessed — among others — the development of rich and powerful cultures, such as the Mochica culture — ADfamous for the construction of monumental ceremonial centers and cultural artefacts such as vessels and metal ornaments .
Camelid skeletal remains were found in different Mochica contexts: Because of the arid to hyper arid conditions that prevail today, the Peruvian coast does not seem to provide favorable conditions to camelid herding, compared to the rich productive grasslands and wet bofedales of the puna.