Urinary fluoride excretion in children aged 4-5 years living at low and high altitude in Nepal

Objectives: A higher prevalence of dental fluorosis has been reported in high altitude communities vs low altitude communities. Therefore, specific changes in the body’s fluoride balance may occur in humans living at high altitude.To quantify the effects of altitude on urinary fluoride excretion (UFE) in children living at high and low altitude in Nepal.
Methods: One-hundred healthy children, aged 4-5 years, were recruited from schools in a low altitude (100m) town, Rajbiraj, and a higher altitude (1500m) town, Banepa, in Nepal. Complete datasets were available for 43 low-altitude-living (LAL) children and 48 higher-altitude-living (HAL) children. Participants were visited at home to collect 24-hour urine, food and drink, and tooth-brushing expectorate samples. Fluoride concentrations of samples were measured by fluoride-ion-selective electrode using an acid-diffusion method for foods and toothbrushing expectorates and a direct method for urine and drinks. Nutritional status was estimated using WHO growth standards. A multivariable-adjusted general linear model was used to quantify mean HAL vs LAL difference in UFE, with covariates of nutritional status, sex and total daily fluoride intake (TDFI).
Results: The mean (SD) TDFI for LAL children was 0.696 (0.361) mg/d vs 0.446 (0.223) mg/day for HAL children (95%CI: 0.131-0.369 mg/day, P<0.0005). In the multivariable adjusted model, mean (SD) UFE was 0.573 (0.321) mg/day for LAL children vs 0.313 (0.316) mg/day for HAL children (95%CI: 0.110-0.411 mg/day, P=0.001). When normalised to body mass, mean (SD) daily UFE was 0.038 (0.022) and 0.021 (0.022) mg/kg/day in LAL and HAL children, respectively (95%CI: 0.007-0.027 mg/kg/day, P=0.001).
Conclusions: Urinary fluoride excretion of Nepalese children living at 1500m was substantially lower than children living at sea level, even after adjusting for differences in TDFI. Therefore, the risk of dental fluorosis for HAL children may be greater than for LAL children due to lower excretion and consequently higher body retention of fluoride. Supported by a grant from The Borrow Foundation.