Effect of exercise on fluoride metabolism in adult humans: a pilot study

An understanding of all aspects of fluoride metabolism is critical to identify its biological effects and avoid fluoride toxicity in humans. Fluoride metabolism and subsequently its body retention may be affected by physiological responses to acute exercise. This pilot study investigated the effect of exercise on plasma fluoride concentration, urinary fluoride excretion and fluoride renal clearance following no exercise and three exercise intensity conditions in nine healthy adults after taking a 1-mg Fluoride tablet. After no, light, moderate and vigorous exercise, respectively, the mean (SD) baseline-adjusted i) plasma fluoride concentration was 9.6(6.3), 11.4(6.3), 15.6(7.7) and 14.9(10.0) ng/ ml; ii) rate of urinary fluoride excretion over 0–8 h was 46(15), 44(22), 34(17) and 36(17) μg/h; and iii) rate of fluoride renal clearance was 26.5(9.0), 27.2(30.4), 13.1(20.4) and 18.3(34.9) ml/ min. The observed trend of a rise in plasma fluoride concentration and decline in rate of fluoride renal clearance with increasing exercise intensity needs to be investigated in a larger trial. This study, which provides the first data on the effect of exercise with different intensities on fluoride metabolism in humans, informs sample size planning for any subsequent definitive trial, by providing a robust estimate of the variability of the effect. Fluoride (F) is a trace element which is naturally present in drinking water and all foods and drinks, especially tea and seafoods, at varying concentrations. Following absorption from the gastrointestinal tract, F is rapidly integrated into calcified tissues which contain 99% of body F. F status is of nutritional and public health significance and the American Dietetic Association 1 has confirmed F as an important element for achieving and maintaining oral and bone health. A major decline in the prevalence and severity of dental caries has been seen in many countries worldwide as a result of appropriate exposure to F in different forms added to drinking water, salt or milk. In the UK, more than 10% of the population receives fluoridated water at a concentration of 1 mg/l and almost 40,000 school children, mainly in deprived areas where the water is not fluoridated, receive fluoridated milk at a dose of 0.5 mg/189 ml milk in order to reduce the prevalence of dental caries. Although low levels of F have an important role in prevention of dental caries, disturbances of enamel development (dental/enamel fluorosis) and bone homeostasis (skeletal fluorosis) can result from excessive retention of F in the body during tooth and bone development. Several factors are known to impact F metabolism and subsequently its retention in the body. An understanding of all aspects of F metabolism is critical to identify the biological effects of F and avoid F toxicity in humans. Almost one-quarter of ingested F is rapidly absorbed from the stomach as hydrogen-fluoride and most of the remainder is absorbed more slowly from the proximal small intestine 2 . Plasma F concentration reaches its peak 30–60 min after F ingestion and returns to pre-ingestion levels during the next