Relevant factors when considering fingernail clippings as a fluoride biomarker

Objectives: To determine thumbnail growth rate and length and to examine the effect of age, gender and fluoride exposure on thumbnail growth rate. Research design: Children aged 2-3 years in fluoridated (F) and non-fluoridated (NF) areas participated. A reference mark was made on the thumbnail and subject age and gender were recorded. Six to eight weeks later measurements were taken and the growth rate was calculated. Analysis of variance (after a logarithmic transformation where appropriate) and linear regression analysis were conducted. Results: The rate of thumbnail growth (mm/week) was 0.7, sd 0.12 (F) and 0.6, sd 0.18 (NF), (p=0.14). The length of the thumbnail was 7.5mm, sd 0.77 (F) and 7.8mm, sd 0.58 (NF), (p=0.28). The mean age (F and NF) was 29.8 months (sd 3.7). There were no relationships between thumbnail growth rate and fluoride status, gender or age (p=0.14; p=0.19; p=0.95). Conclusions: There was a wide variation in growth rate and length of thumbnails. Age, gender and fluoride exposure had no effect on thumbnail growth rates. Fingernail growth rate and length should be measured for each subject when using fingernails to estimate fluoride absorption.