Hair as biomarker of fluoride exposure in a fluoride endemic area and a low fluoridated area.

AIM: The aim of the present study was to determine whether hair could be used as biomarker of fluoride exposure.
MATERIALS AND METHODS: The study was carried out on 30 people living in an endemically fluoridated area and a low fluoridated area. Samples of hair from the occipital were taken and subjected to fluoride analysis by a fluoride ion electrode.
RESULTS: Lower fluoride levels in water supplies correlated with lower levels of fluoride in hair and more over higher fluoride levels in water correlated with higher levels of fluoride in hair. A direct relationship was evident between fluoride levels in water supplies and concentration of fluoride in hair (P < 0.01).
CONCLUSIONS: The results of the present study indicate hair can be used as an indicator of fluoride exposure.

INTRODUCTION

There has been a decline in dental caries prevalence and incidence in the developed countries over the last 2 decades. This decrease is considered to be largely due to the widespread use of fluorides. Concurrent with the decline in caries, an increase in the prevalence of dental fluorosis has been noted. Although fluorides have played a central role in oral health promotion for the past 50 years, ingestion of excessive fluoride during tooth development, particularly at the maturation stage may result in dental fluorosis, which has an extensive range of clinical signs. This has led to the search for biomarkers of fluoride exposure in various body tissues such as teeth, bone, nail, hair, plasma, urine, saliva.

Biomarker is an indicator of change in biological system that could lead to a clinical disease. Biomarkers will aid in prevention of future disease by providing evidence for preclinical disease at early preventable stage. Biomarker is defined as “cellular, bio chemical or molecular alterations measurable in biological media such as human tissues, cells or fluids.”[1]

Fluoride can be measured in many different biological media, including urine, saliva, bone, blood, hair and nails.[2345] Hair sampling is simple and non-invasive, and there are many reports suggesting the use of nails and hair as biomarkers for fluoride exposure in humans.[367]

MATERIALS AND METHODS

Fluoride concentrations in the hair of 30 people which consist of 19 men and 11 women in a fluoride endemic area (15 people) and a low fluoridated area (15 people) were determined. The mean age of the examined group was 47.5 years (range 35-60). Samples of hair of minimal length 2-3 cm were taken from the occipital region. The individuals also completed a questionnaire asking for general data: Age, gender, water supply and place of residence, nutrition and oral hygienic habits. The concentration of fluoride in drinking water in the fluoride endemic region is 5.2 ppm and that in the low concentrated region ranged from 0.3 to 0.5 ppm, which was estimated by the Regional Public Health laboratory.

Analytical procedure for hair

Samples of hair were placed on a fritted glass filter and then rinsed with acetone, detergent, 2N sulfuric acid and redistilled water. After drying 100 mg aliquots were placed into test tubes, treated with concentrated sodium hydroxide solution and heated in a boiling water bath until complete solution (hair - 60 min). Cooled and neutralized with 1 M HCl acid and the sample volumes made up with water to 4 ml and diluted with equal volumes of total ionic strength adjustment buffer. Fluoride concentrations were measured by a fluoride ion specific electrode and an Ag/AgCl reference electrode with a double jacket. Calculations were based on a response factor from a standard curve. Recovery of fluoride from analyzed material amounted to 100 ± 8%. The data are expressed as mean ± SD The significance level was established at 5%. Significance was determined by Student's t-test.

Ethical approval

The ethical approval was obtained from the Ethical Committee and informed consent was obtained from the subjects.

RESULTS

The study sample consisted of 30 people, 15 from the endemically fluoridated area and 15 from the low fluoridated area. The mean age in the sample is 49.33 years [Table 1]. Out of the 30 subjects, 19 are males and 11 females [Table 2]. The fluoride content in hair of the subjects living in endemic fluoridated area was significantly increased when compared to controls. The mean hair fluoride levels in endemic fluoridated area is 2171.83 ug/g when compared to the hair fluoride levels in low fluoridated area which is 25.06 ug/g [Table 3]. The low fluoride levels in water supplies correlated with lower fluoride levels in hair and the higher fluoride levels in water correlated with higher fluoride levels in hair in subjects of endemically fluoridated area. Overall comparison of hair among male and female in endemic and low fluoridated areas showed statistically insignificant results [Table 4].

Table 1

Distribution of study samples by age groups in two groups

Table 2

Distribution of study samples by sex in two groups

Table 3

Comparison of study groups with respect to readings related to hairs scores

Table 4

Comparison of male and female subjects with respect to readings related to hairs in endemic fluoridated area and low fluoride area groups

DISCUSSION

The main source of fluoride intake by humans is the drinking water. Therefore, the concentration of fluoride was determined in the water in both the regions. The fluoride concentration in the endemic area was 5.2 ppm where as it ranged from 0.3 to 0.5 in low concentrated area. The source of water in both the regions was bore well water. In our study, the fluoride content in the subjects of endemically fluoridated area was much higher than the subjects of low fluoridated area which is similar to studies by Czarnowski et al.[3] and Kokot et al.[6]

An individual variation may be caused by considerable differences in absorption, distribution and excretion of fluorides or by differences in eating and drinking habits and work practices. Statistical analysis showed no correlation between the concentration of fluoride in hair and the intake of fish, tea and toothpaste used.

Collection of hair is not only simple and non-invasive, but also easy to transport and store. Moreover, the fluoride content of hair provides information on long-term exposure, in contrast to transient information from blood and urine samples.

CONCLUSION

The results seem to indicate that a considerable increase in fluoride content in subjects of endemic fluoride area than in the low fluoridated area. By far the highest increment was noticed in the hair of subjects of endemically fluoridated area. Taking into account the availability of this material, hair may be regarded as a useful material in evaluating prolonged exposure to fluorine compounds.