Fluctuating daily urinary fluoride concentrations in fluoridated and non-fluoridated areas

Objectives: Due to the challenges of collecting 24-hour urine samples for monitoring fluoride exposure in children, spot urine (SU) has been suggested as an alternative collection method. However, urinary fluoride concentration (UFC) may vary during the day. This study aimed to evaluate the daily fluctuation in UFC in naturally fluoridated (FA) and non-fluoridated (NFA) areas of the UK. Methods: SU samples were collected from healthy children, aged 4-6y, living in FA (n = 28) and NFA (n = 36) areas of the UK. Participants provided four SU samples: (i) fasting (ii) 3h after breakfast, (iii) 3h after lunch, and (iv) last urine before going to bed. Samples were analysed in triplicate, using an F- ion-selective electrode and direct method. Results: Mean (SD) fluoride concentration of tap water was 1.232 (0.057) and 0.107 (0.031) µg/g for FA and NFA, respectively. The highest mean (SD) UFC of 1.460 (0.618) µg/g during fasting and the lowest of 1.218 (0.604) µg/g 3h after lunch were recorded in the FA. The highest mean (SD) UFC of 1.442 (1.729) µg/g 3h after breakfast and the lowest of 1.141 (1.105) µg/g 3h after lunch were recorded for the NFA. Daily variation in UFC ranged from 0.373 to 3.997 µg/g and 0.058 to 8.869 µg/g for FA and NFA, respectively.

Conclusion: This study evaluated the daily fluctuation in urinary fluoride concentration for FA and NFA. The wide fluctuations in daily urinary fluoride concentration highlight the need to collect SU samples at several timepoints throughout the day.