Fluoride balance studies in ambulatory healthy men with and without fluoride supplements

Environmental fluoride exposure and implications on potential pediatric kidney health risks: an approach with urinary biomarkers

BACKGROUND

Environmental fluoride exposure at elevated levels is potentially linked to kidney injury, and may contribute to chronic kidney disease of uncertain etiology (CKDu) as a risk factor. However, this link remains unclear, and examining the risk of kidney damage from early life fluoride exposure may provide important insights. Hence, this study aimed to investigate associations of fluoride exposure with pediatric kidney health in CKDu impacted and unimpacted communities in Sri Lanka.

METHODS

Considering the geographical variations in environmental fluoride, climate, and prevalence of CKDu, four study groups were established within selected education zones in CKDu-endemic dry zone regions (D-En), and CKDu-nonendemic regions within the dry (D-NE), wet (W-NE), and intermediate (I-NE) climatic zones. The study population included 922 school students (11-18 years of age). Participants in each group were divided into four subgroups based on quartiles of respective urinary fluoride (UF) distribution for comparison of urinary kidney injury molecule-1 (KIM-1), neutrophil gelatinase-associated lipocalin (NGAL), and albumin-creatinine ratio (ACR).

RESULTS

UF levels in participants particularly in CKDu endemic dry zone regions were significantly high compared to the other regions. Significantly high median urinary NGAL (in D-NE) and ACR (in D-EN, and W-NE) levels were observed in subgroups of higher UF quartiles. Albuminuria was not particularly identified in subjects with high UF excretion. Urinary KIM-1 showed no significant variation across the UF quartile subgroups. Linear regression identified weak associations of UF with kidney injury biomarkers.

CONCLUSIONS

Fluoride exposure is particularly high in CKDu-endemic dry zone communities. As implied by kidney injury biomarkers, a strong link between fluoride exposure and pediatric kidney health was not evident at the observed exposure levels in the study regions.

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.

Total fluoride intake and urinary excretion in 4–year–old Iranian children residing in low-fluoride areas

Knowledge of levels of fluoride ingestion and excretion is important in planning optimum fluoride therapy for young children. In previous literature, it has been assumed that only about one-third of ingested fluoride is excreted in young children. The aims of the present study were (a) to measure total fluoride intake, urinary fluoride excretion and fluoride balance, and (b) to investigate the effect of air temperature on fluoride intake and urinary fluoride excretion, in young children. Children (4 years old) living in a city, a small town and rural areas of Fars province, Iran, where drinking water contained 0·30–0·39 mg F/l, were invited to participate. Selection of subjects was by random sampling of kindergartens or health centres. The children were surveyed twice, once in summer and once in winter. Diet was obtained by 3 d diaries with interview. Samples of most foods and drinks were analysed for fluoride content. Ingestion of fluoride from toothpaste was estimated for each child. Each child's urine was collected over 24 h and analysed for fluoride content. Seventy-eight of the 116 volunteers completed all aspects of the study, which was conducted in 1995–6. For all children, the mean fluoride ingestion from diet was 0·390 (sd 0·122) mg/d or 0·028 (sd 0·008) mg/kg body weight per d. Fluoride ingestion from diet was higher in summer and higher in rural areas. The mean ingestion of fluoride from all sources was 0·426 (sd 0·126) mg/d and the mean fluoride urinary excretion was 0·339 (sd 0·100) mg/d. The difference between ingestion and urinary excretion was +0·087 (sd 0·143) mg, equivalent to 80 % excretion. Faecal excretion was not estimated. The results indicate fluoride retention at 4 years to be much lower than previously assumed.

Fluoride and fluoridation

To date, many of the ways of controlling tooth decay involve the use of fluorides. Either systemically via fluoridated water and tablets, or, topically, with fluoride-containing toothpaste and mouthrinses. There is now evidence that the prevalence of dental caries is declining in communities with unfluoridated water, as well as in those with fluoridated water. This phenomenon may be related to an increase of fluoride in the food chain; the unintentional ingestion of fluoride-containing dental health products; and the increasing contamination of the total environment with fluoride emissions and solid wastes from many industries. The apparent usefulness of fluoride as a preventive against dental caries does not mean that unnecessary exposure to the element should be tolerated. Fluoride at very low concentrations is phytotoxic and harmful to livestock; and in man, excessive intakes of fluoride over many years may lead to a well-defined disorder--skeletal fluorosis. In addition, a number of recent studies have suggested that fluoride may be genotoxic.

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.