Fluoride intake and urinary excretion in 6- to 7-year-old children living in optimally, sub-optimally and non-fluoridated areas.

OBJECTIVES: This study was designed to measure total intake, urinary excretion and estimated retention of fluoride in children under customary fluoride intake conditions, living in either fluoridated or low-fluoride areas of north-east England. Subsidiary aims were to investigate the relationships between the variables measured.
METHODS: Using a randomized cluster design with schools as the sampling units, four schools from a non-fluoridated area and two from a fluoridated area were selected from the schools chosen to participate in the study. Fluoride intake from diet and toothbrushing was assessed using a 3-day food diary and fluoride analysis of expectorated saliva during toothbrushing. Samples of all foods and drinks consumed were measured for fluoride content using direct and indirect silicon-facilitated diffusion methods as appropriate. Urinary fluoride excretion and urine volume were measured over 24 h and estimation of fractional urinary fluoride excretion (FUFE) and fluoride retention made from collected data. Following descriptive analysis of variables, Pearson's correlations investigated relationships between fluoride content of home tap water, daily fluoride intake, excretion and retention.
RESULTS: Thirty-three children completed the study: 18 receiving non-fluoridated water [mean = 0.08 (+/-0.03) mg F/l], nine sub-optimally fluoridated water [mean = 0.47 (+/-0.09) mg F/l] and six optimally fluoridated water [mean = 0.82 (+/-0.13) mg F/l] at the time of the study. Complete data on F intake, excretion and retention were available for 29 children. Mean fluoride intake from diet and toothpaste ranged from 0.031 (+/-0.025) mg/kg body weight (bw)/day for the low-fluoride area to 0.038 (+/-0.038) and 0.047(+/-0.008) mg/kg bw/day for sub-optimally and optimally fluoridated areas respectively. Contribution of toothpaste to total fluoride intake ranged from 3% to 93% with mean values of 57%, 35% and 47% for children receiving low, sub-optimally and optimally fluoridated water respectively. FUFE ranged from a mean of 32% (+/-13%) for the optimally fluoridated area to 44% (+/-33%) for the low-fluoride area. Fluoride retention was not correlated with the fluoride concentration of home water supply, but was strongly positively correlated (P < 0.001) with total daily fluoride intake.
CONCLUSIONS: In an industrialized country, total fluoride intake, urinary excretion and consequently fluoride retention no longer reflect residence in a community with a non-fluoridated or fluoridated water supply. Fluoride toothpaste contributes a significant proportion of total ingested fluoride in children, particularly in low-fluoride areas.