Influence of Growth Rate and Length on Fluoride Detection in Human Nails

Abstract

This study aimed to determine the lag time between increased fluoride (F) intake and F detection in human nails, as well as the influence of nails growth rate and length on this. Ten 20- to 35-year-old volunteers received 1.8 mg F daily, for 30 days. Nail growth rate and length were determined for all fingernails and toenails. Nail samples were collected at the beginning of the study and every 2 weeks (15 collections in all) and F concentrations were determined. The growth rate was statistically higher in fingernails than in toenails. No statistically significant differences were observed between right and left sides. Growth rate was significantly greater for big toenails than for the other toenails, but this pattern was not found for fingernails. The estimated mean lag times for F detection in fingernails and toenails were 101 and 123 days, respectively. An apparent increase in fingernail F concentrations was observed 84 days after the beginning of the study, although this was not statistically different from baseline. For toenails, statistically significant increases in F concentration in relation to baseline were observed 112 and 140 days after increased F ingestion. These increases occurred within the 95% confidence intervals for the calculated mean lag time for fluoride detection in nails. Considering the large amount of sample provided by the big toenails, together with their faster growth rate, as well as the fact that toenails are less prone to environmental contamination, our data suggest that big toenails are more suitable biomarkers of fluoride intake.

The Effect of Different Fluoride Concentrations and pH of Dentifrices on Plaque and Nail Fluoride Levels in Young Children

“…A recent study has shown that this is not the case [Olympio et al, 2007]. In the present study, the results of Olympio et al [2007] were confirmed using nail F concentrations as response variables, since nails have been used as biomarkers of chronic [Whitford et al, 1999;Levy et al, 2004] and subchronic [Whitford et al, 1999;Correa Rodrigues et al, 2004;Buzalaf et al, 2006] F intake. Our results confirm that dentifrice pH does not seem to influence bioavailability of F, since nail F concentrations with the 1,100 ppm F ELDs were nearly identical, whether the pH was 4.5 or 7.0.…”

Environmental and Individual Factors Associated with Nail Fluoride Concentration

“…Especially for F, nail clippings could play a relevant role to monitor F exposure and estimate risk for fluorosis. There are reports suggesting the use of nails as a biomarker for F exposure in animals [Buzalaf et al, 2002 and humans [Schamschula et al, 1985;Machoy, 1989;Czarnowski and Krechniak, 1990;Schmidt and Leuschke, 1990;Spate et al, 1994;Whitford et al, 1999;Levy et al, 2004;Rodrigues et al, 2004;Buzalaf et al, 2006]. Both fingernails and toenails have been used for this purpose, but the literature is contradictory regarding the relationship between fingernail and toenail F concentrations [Machoy, 1989;Whitford et al, 1999;Levy et al, 2004;Rodrigues et al, 2004;Buzalaf et al, 2006].…”

Fingernail may not be a reliable biomarker of fluoride body burden from dentifrice

“…Mean ± SD and (95% confidence interval) of F dose (mg F/kg body weight/day) to which children were exposed in phase A (diet +dentifrice) and in phase B (diet), and F concentration in fingernails (µg F/g) formed during these respective phases α (n = 23). that some studies have found a relationship between F exposure and F concentrations in fingernails (8,10), but others not (10,12). It should be emphasized that in the present study, it was estimated the dose to which the children were exposed from the dentifrice considering the soluble F concentration found in the dentifrice and not the one reported by the manufacturer because the dentifrice used contained calcium and part of F was insoluble.…”

“…However, data available in the literature are conflicting about their use to estimate the effect of F intake during toothbrushing (8)(9)(10)(11).…”

“…In another study, using the same protocol, fingernails did not have sensitivity to detect F exposure from dentifrice or F varnish (9). No significant increase of F concentration in fingernails was observed in adults who ingested 1.8 mg F for 30 days either, but surprisingly the authors concluded that fingernails could be considered a biomarker for F based on two nails clippings that were within the 95% confidence interval calculated (10). Furthermore, when F intake from diet and dentifrice was evaluated in young children, there was no association between F concentration in fingernails and F intake (11).…”