In the Swiss canton of Vaud (512000 inhabitants) the salt available for human consumption has been fluoridated since 1969 by adding 250 mg F- per kg of salt. The urinary excretion of fluoride has been investigated in large samples of the population in 1970 and in 1974. The present study reports the results of the 1974 study, in which the urinary fluoride excretion of persons living in the canton of Vaud was compared to that of a smaller sample of people living in small townships across the border of the canton, in which neither edible salt nor water are fluoridated. The concentration of fluoride in 444 single samples of urine from adult persons living in the canton of Vaud was 1.06 +/- 0.03 mg/l, in 40 subjects living two townships across the border 0.62 +/- 0.06 mg/l. The excretion of fluoride per 24 hrs has been evaluated by measuring simultaneously the creatinine concentration in the urine samples under the assumption of constant creatinine and fluoride excretion within 24 hour periods. The calculated fluoride excretion in 366 subjects living in the canton of Vaud was 1.14 +/- 0.03 mg/24 hrs, that of 40 subjects living outside of the canton 0.60 +/- 0.05 mg/24 hrs when the figure inserted for the excretion of creatinine within 24 hours was taken from a study of Rowe [9]. A few data reported suggest that the mean excretion of creatinine in the urine of normal subjects living in Switzerland was only 67% of that measured in the U.S. by Rowe. Total fluoride excretions calculated under this assumption were 0.76 +/- 0.02 mg/24 hrs for persons living in Vaud vs. 0.40 +/- 0.04 mg/24 hrs in the subjects living outside of Vaud. The concentrations of fluoride found in the urine of the adult subjects of the present study did not differ significantly from those found in school children aged 7-15 living in the same communities. Concentrations of fluoride in urine appear to have increased since 1970 in subjects living in the canton of Vaud. This fact may indicate that a steady state equality between intake and urinary excretion of fluoride had not yet been reached in 1970. In 366 urine samples of subjects living in Vaud in 1974, the concentration of fluoride in urine could be represented as a linear regression on the concentration of creatinine. The slope of this regression was smaller than unity indicating an enhanced fluoride excretion at higher rates of urine flow and a depressed excretion at low rates of urine flow. The occurrence of diurnal variations in the urinary excretion of fluoride or of creatinine could not be excluded in the present study. The urinary excretion of fluoride exceeded 2.5 mg/24 hr in approximately 2% of the subjects living in the canton of Vaud but was smaller than 0.8 mg/24 hr in approximately 18%. It was concluded that fluoridation of salt at the level indicated should be an effective measure for the prevention of dental caries. It was, furthermore, concluded that salt fluoridation at the level indicated does not present any risk of toxicity.
