Fractional urinary fluoride excretion of 6-7-year-old children attending schools in low-fluoride and naturally fluoridated areas in the UK

F is an important trace element for bones and teeth. The protective effect of F against dental caries is well established. Urine is the prime vehicle for the excretion of F from the body; however, the relationship between F intake and excretion is complex: the derived fractional urinary F excretion (FUFE) aids understanding of this in different age groups. The present study aimed to investigate the relationships between (1) total daily F intake (TDFI) and daily urinary F excretion (DUFE), and (2) TDFI and FUFE in 6-7-year-olds, recruited in low-F and naturally fluoridated (natural-F) areas in north-east England. TDFI from diet and toothbrushing and DUFE were assessed through F analysis of duplicate dietary plate, toothbrushing expectorate and urine samples using a F-ion-selective electrode. FUFE was calculated as the ratio between DUFE and TDFI. Pearson's correlation and regression analysis were used to investigate the relationship between TDFI and FUFE. A group of thirty-three children completed the study; twenty-one receiving low-F water (0.30 mg F/l) and twelve receiving natural-F water (1.06 mg F/l) at school. The mean TDFI was 0.076 (sd 0.038) and 0.038 (sd 0.027) mg/kg per d for the natural-F and low-F groups, respectively. The mean DUFE was 0.017 (sd 0.007) and 0.012 (sd 0.006) mg/kg per d for the natural-F and low-F groups, respectively. FUFE was lower in the natural-F group (30 %) compared with the low-F group (40 %). Pearson's correlation coefficient for (1) TDFI and DUFE was +0.22 (P= 0.22) and for (2) TDFI and FUFE was-0.63 (P< 0.001). In conclusion, there was no correlation between TDFI and DUFE. However, there was a statistically significant negative correlation between FUFE and TDFI.