<unk>  does not affect the appearance, taste or smell of drinking<unk> .<unk>  is the controlled adjustment of fluoride to a public<unk>  supply solely to reduce tooth decay. Fluoridated<unk>  contains fluoride at a level that is effective for preventing cavities; this can occur naturally or by adding fluoride. Fluoridated<unk>  operates on tooth surfaces: in the mouth, it creates low levels of fluoride in saliva, which reduces the rate at which tooth enamel demineralizes and increases the rate at which it remineralizes in the early stages of cavities. Typically a fluoridated compound is added to drinking<unk> , a process that in the U.S. costs an average of about $ per person-year. Defluoridation is needed when the naturally occurring fluoride level exceeds recommended limits. In 2011, the World Health Organization suggested a level of fluoride from 0.5 to 1.5 mg/L (milligrams per litre), depending on climate, local environment, and other sources of fluoride. Bottled<unk>  typically has unknown fluoride levels. Tooth decay remains a major public health concern in most industrialized countries, affecting 60–90% of schoolchildren and the vast majority of adults.<unk>  reduces cavities in children, while efficacy in adults is less clear. A Cochrane review estimates a reduction in cavities when<unk>  was used by children who had no access to other sources of fluoride to be 35% in baby teeth and 26% in permanent teeth. However, this was based on older studies which failed to control for numerous variables, such as increasing sugar consumption as well as other dental strategies. Most European countries have experienced substantial declines in tooth decay, though milk and salt<unk>  is widespread in lieu of<unk> . Recent studies suggest that<unk> , particularly in industrialized nations, may be unnecessary because topical fluorides (such as in toothpaste) are widely used, and caries rates have become low. Although<unk>  can cause dental fluorosis, which can alter the appearance of developing teeth or enamel fluorosis, the differences are mild and usually not an aesthetic or public health concern. There is no clear evidence of other side effects from<unk> . Fluoride's effects depend on the total daily intake of fluoride from all sources. Drinking<unk>  is typically the largest source; other methods of fluoride therapy include<unk>  of toothpaste, salt, and milk. The views on the most efficient method for community prevention of tooth decay are mixed. The Australian government states that<unk>  is the most effective way to achieve fluoride exposure that is community-wide. The World Health Organization reports that<unk> , when feasible and culturally acceptable, has substantial advantages, especially for subgroups at high risk, while the European Commission finds no benefit to<unk>  compared with topical use. Public<unk>  was first practiced in the U.S. As of 2012, 25 countries have artificial<unk>  to varying degrees, 11 of them have more than 50% of their population drinking fluoridated<unk> . A further 28 countries have<unk>  that is naturally fluoridated, though in many of them the fluoride is above the optimal level. As of 2012, about 435 million people worldwide received<unk>  fluoridated at the recommended level (i.e., about 5.4% of the global population). About 214 million of them live in the United States. Major health organizations such as the World Health Organization and FDI World Dental Federation supported<unk>  as safe and effective. The Centers for Disease Control and Prevention lists<unk>  as one of the ten great public health achievements of the 20th century in the U.S. Despite this, the practice is controversial as a public health measure. Some countries and communities have discontinued<unk> , while others have expanded it. Opponents of the practice argue that neither the benefits nor the risks have been studied adequately, and debate the conflict between what might be considered mass medication and individual liberties.
Water fluoridation
Phosphate supplement
Food fortification
Feingold diet
Iron supplement
Protein supplement
Cobalt therapy
Ultraviolet light therapy