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As with some other countries, water fluoridation in the United States is a contentious issue. As of May 2000, 42 of the 50 largest U.S. cities had water fluoridation. On January 25, 1945, Grand Rapids, Michigan, became the first community in the United States to fluoridate its drinking water to prevent tooth decay. Fluoridation became an official policy of the U.S. Public Health Service by 1951, and by 1960 water fluoridation had become widely used in the U.S., reaching about 50 million people. By 2006, 69.2% of the U.S. population on public water systems were receiving fluoridated water, amounting to 61.5% of the total U.S. population. Near the end of 2012, 67.1% of the U.S. population were getting water from community water systems (CWS) supplying water that had fluoride at or above recommended levels. Those included the 3.5% of the population that were on CWS with naturally-occurring fluoride at or above recommended levels. 74.6% of those on CWS were receiving water with fluoride at or above recommended levels.〔(【引用サイトリンク】title=Community Water Fluoridation --- 2012 Water Fluoridation Statistics )〕 U.S. regulations for bottled water do not require disclosing fluoride content.〔 A survey of bottled water in Cleveland and in Iowa, published in 2000, found that most had fluoride levels well below the 1 mg/L level common in tap waters. == History == (詳細はHistory of Dentistry in the Pikes Peak Region ),(Colorado Springs Dental Society ) webpage, page accessed February 25, 2006.〕 The condition, now known as dental fluorosis, when in its severe form is characterized by cracking and pitting of the teeth.〔()〕〔(McGraw-Hill's AccessScience )〕〔(Report Judges Allowable Fluoride Levels in Water : NPR )〕 Of 2,945 children examined in 1909 by Dr. McKay, 87.5% had some degree of stain or mottling. All the affected children were from the Pikes Peak region. Despite the negative impact on the physical appearance of their teeth, the children with stained, mottled and pitted teeth also had fewer cavities than other children. McKay brought this to the attention of Greene Vardiman Black, and Black's interest was followed by greater interest within the dental profession. Initial hypotheses for the staining included poor nutrition, overconsumption of pork or milk, radium exposure, childhood diseases, or a calcium deficiency in the local drinking water.〔 In 1931, researchers from the Aluminum Company of America (ALCOA) concluded that the cause of the Colorado stain was a high concentration of fluoride ions in the region's drinking water (ranging from 2 to 13.7 mg/L) and areas with lower concentrations had no staining (1 mg/L or less).〔Meiers, Peter: ("The Bauxite Story – A look at ALCOA" ), from the (Fluoride History ) website, page accessed May 12, 2006.〕 Pikes Peak's rock formations contained the mineral cryolite, one of whose constituents is fluorine. As the rain and snow fell, the resulting runoff water dissolved fluoride which made its way into the water supply. Dental and aluminum researchers then moved toward determining a relatively safe level of fluoride to be added to water supplies. The research had two goals: (1) to warn communities with a high concentration of fluoride of the danger, initiating a reduction of the fluoride levels in order to reduce incidences of fluorosis, and (2) to encourage communities with a low concentration of fluoride in drinking water to add fluoride in order to help prevent tooth decay. By 2006, 69.2% of the U.S. population on public water systems were receiving fluoridated water, amounting to 61.5% of the total U.S. population; 3.0% of the population on public water systems were receiving naturally occurring fluoride.〔 In April 2015, fluoride levels in the United States were lowered for the first time in 50 years, to the minimum recommended levels of 0.7ppm, because too much fluoride exposure has become a common issue for children teeth, visible in the form of white splotches. The basis were the results of two national surveys (1999–2004 NHANES) which assessed the prevalence of dental fluorosis, and found that two out of five adolescents had tooth streaking or spottiness on their teeth - an increase of mostly very mild or mild forms.〔(【引用サイトリンク】title=US lowers fluoride levels in drinking water for first time in over 50 years )〕〔(【引用サイトリンク】url=() () )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Water fluoridation in the United States」の詳細全文を読む スポンサード リンク
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