Fluoridation opponents questioned the ethics, safety, and efficacy of fluoridation. Fluoridation of water has its critics (see Water fluoridation controversy). Water fluoridation and fluoride supplements decrease the incidence of dental caries. Fluoridation chemicals may also contain aluminum fluoride. For example, fluoride containing compounds are dissolved to supply fluoride ions for water fluoridation. The fluoride is sometimes recovered for use in water fluoridation. Systemic fluoride is found as lozenges, tablets, drops and water fluoridation. Water and food sources of fluoride include community water fluoridation, seafood, tea, and gelatin. Some chiropractors oppose vaccination and water fluoridation, which are common public health practices. Existing evidence suggests that water fluoridation reduces tooth decay. The NHF also opposes interventions such as water fluoridation and childhood vaccines. Further research showed that moderate fluoridation prevents tooth decay. Early opposition to water fluoridation included chiropractors in the U.S. He does however support more depth in the research literature related to municipal water fluoridation. There is no clear evidence of other adverse effects from water fluoridation.