Water fluoridation
Many areas in China have fluoride at levels far higher than recommended due to natural occurrence or industrial contamination, which has resulted in high incidences of skeletal fluorosis. Water fluoridation levels are set at a national standard of 1 mg/L, with higher levels for rural areas at 1.2 mg/L. Water fluoridation began in 1965 in the urban area of Guangzhou. It was interrupted during 1976–1978 due to the shortage of sodium silico-fluoride. It was resumed only in the Fangcun district of the city, but was halted in 1983 after opponents claimed that fluoride levels were already sufficiently high in local foods and tea. Later analysis in 1988 found that the incidence of dental caries among 4-year-old children had increased by 62%. The fluoridation reduced the number of cavities, but increased dental fluorosis; the fluoride levels could have been set too high, and low-quality equipment led to inconsistent, and often excessive, fluoride concentrations.