Fluoride balance studies in healthy men during bed rest with and without a fluoride supplement

The use of urinary fluoride excretion to facilitate monitoring fluoride intake: A systematic scoping review

BACKGROUND

As a recognised effective and economical agent for dental caries prevention, fluoride has been used in many different fluoridation schemes implemented across the world. Considering the narrow 'dose-gap' between the benefit of caries reduction and the risk of dental fluorosis, it is recommended that fluoride intake is monitored by measuring urinary fluoride excretion. The aim of this scoping review is to map the current literature/evidence on fluoride intake and excretion studies in relation to the study population, settings, type of study design, methodology, and analytical approach.

METHODS

Embase/Ovid, MEDLINE/Ovid, CINAHL/EBSCO, Scopus/Elsevier were searched for relevant articles until April 2018. Studies were included if they reported intake and excretion of fluoride in healthy humans of all age groups. Findings were explored using a narrative synthesis to summarise studies characteristics and outcome measures.

RESULTS

Removal of duplicates from the originally 2295 identified records yielded 1093 studies of which 206 articles were included. Only 21.6% of the studies were conducted in children (<8-year-olds). Most studies (38.8%) used drinking water concentration as a proxy for fluoride intake, whereas only 11.7% measured fluoride intake from all sources. Of the 72 studies that measured dietary fluoride intake, only 10 reported the validity of the employed dietary assessment method. Only 14 studies validated the urine sample collection methods. No information on the validity of the employed analytical method was reported by the majority (64.6%) of studies. Only a small proportion (8.7%) of the included studies investigated the association between fluoride intake and excretion.

CONCLUSION

The findings reveal much variability in terms of conducting the studies and reporting the findings, illustrating a high heterogeneity in data collection across settings and populations. Future studies should provide more detail on sampling technique, measurement protocols (including validation), and on clearly defining the relationship between intake and urinary excretion of fluoride.

Effects of microgravity on bone and calcium homeostasis

Mechanical function is known to be of crucial importance for the maintenance of bone tissue. Gravity on one hand and muscular effort on the other hand are required for normal skeletal structure. It has been shown by numerous experimental studies that loss of total-body calcium, and marked skeletal changes occur in people who have flown in space. However, most of the pertinent investigations have been conducted on animal models, including rats and non-human primates, and a reasonably clear picture of bone response to spaceflight has emerged during the past few years. Osteopenia induced by microgravity was found to be associated with reduction in both cortical and trabecular bone formation, alteration in mineralization patterns and disorganization of collagen, and non-collagenous protein metabolism. Recently, cell-culture techniques have offered a direct approach of altered gravity effects at the osteoblastic-cell level. But the fundamental mechanisms by which bone and calcium are lost during spaceflight are not yet fully known. Infrequency and high financial cost of flights have created the necessity to develop on-Earth models designed to mimic weightlessness effects. Antiorthostatic suspension devices are now commonly used to obtain hindlimb unloading in rats, with skeletal effects similar to those observed after spaceflight. Therefore, actual and "simulated" spaceflights, with investigations conducted at whole body and cellular levels, are needed to elucidate pathogeny of bone loss in space, to develop effective countermeasures, and to study recovery processes of bone changes after return to Earth.

Pharmacology in space: pharmacotherapy

This chapter summarized the information available on the pharmacological kits onboard spacecraft and on the use of drugs in space, while the next chapter is dedicated to the impacts of weightlessness on drug pharmacokinetics. The need of a selected group of drugs for the use of astronauts during short-term and long-term spaceflights has been discussed. Recommendations are made for a Space Pharmacopoeia as well as for the areas of research needed to adapt medication to the weightlessness of the space environment. Although the usefulness of these drugs has been clearly demonstrated, their use also raises several problems. Physiological changes due to weightlessness may induce changes in pharmacokinetic behavior of drugs and influence their dosage regimen. Inflight data obtained by salivary drug monitoring have shown changes in the distribution of scopolamine and a significant change in the disposition of the common pain-relief agent acetaminophen taken inflight, in both drug concentration and time course. The authors of this study emphasize, however, that their data are preliminary and as yet incomplete. Further simulation studies and, if possible, inflight experiments are required. In vitro studies of the antibacterial activity of antibiotics under space conditions have shown an increased resistance of Escherichia Coli to colistin and kanamycin, and a lowered resistance of Staphylococcus Aureus to oxacillin, chloramphenicol, and erythromycin. The possible consequences of these findings for the treatment of infections contracted by astronauts are yet to be elucidated. There is still a lack of pharmacological countermeasures, particularly for preventing the progressive bone demineralization occurring in weightlessness. The treatment of space motion sickness with drugs carries with it the problem of undesirable side-effects on psychomotor performance. In order to arrive at the most appropriate medical kit for a particular mission, the best trade-off of risk versus benefit for the individual and the mission must always be attempted for any pharmacological agent.

Effect of dichloromethylene diphosphonate on fluoride balance in healthy men

Healthy men with a daily intake of 0.37 mg fluoride were given dichloromethylene diphosphonate (Cl2MDP) or a placebo during a period of ambulation followed by bed rest. In both groups, serum ionic fluoride was unchanged, and fluoride balances were negative, but Cl2MDP significantly reduced loss of fluoride in the treated groups.