Total- and Fractional-Fluoride-Retention in Weaned Infants

Objectives: An increased Fluoride (F) intake during infancy may have contributed to the rise in prevalence of dental fluorosis in both fluoridated and non-fluoridated communities over recent decades. In monitoring F exposure, assessment of the fraction of F intake retained in the body might be more important than absolute F intake as several factors can impact F absorption, excretion and retention rates. Therefore, the study aimed to estimate total-F-retention (TFR) and fractional-F-retention (FFR) of weaned infants in north-east England.
Methods: Weaned infants, aged 9-12 months, were recruited. Total F intake (TFI) over a 48h period, from diet and toothpaste ingestion, was assessed using a dietary-diary and a tooth-brushing questionnaire. Total F excretion (TFE) was estimated by collecting 48h urine and faeces. F concentrations of food/drinks samples consumed by infants and faeces collected over the 48h were measured by the acid-diffusion method, with F assay of urine and water samples using a direct method with F-ion-selective electrode. TFR was estimated by subtracting TFE from TFI and FFR was estimated as the ratio between TFR and TFI.
Results: Thirty-three infants (mean (SD) age: 10.6 (1.2) months) participated; 16 breast-fed, 12 formula-fed and 2 mixed-fed. Mean (SD) F concentration of supply water was 0.6 (0.4)mg/L. Mean (SD) TFI, TFE and TFR of breast-fed infants were 0.036 (0.027), 0.011 (0.009) and 0.025 (0.019) mg/kgbw/d, respectively. Corresponding figures were 0.076 (0.038), 0.023 (0.009) and 0.052 (0.033) mg/kgbw/d for formula-fed and 0.029 (0.004), 0.013 (0.005) and 0.016 (0.009) mg/kgbw/d for mixed-fed infants. Mean (SD) FFR was 64(17)% for all 33 infants (breast-fed: 65(19)%, formula-fed: 64(15)%, mixed-fed: 52(23)%).
Conclusions: In weaned infants, a relatively large proportion (64%) of F intake is retained in the body (i.e. deposited in calcifying tissues) which should be considered when implementing F-based prevention therapies with the goals of maximising caries prevention while minimising dental fluorosis risk.