EAL

FL: Fluoride and the Renal System (2010)

Citation:

Study Design:

Class:

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Quality Rating:

Research Purpose:

To explore the dose-effect relationship between drinking water fluoride levels and damage to human liver and kidney function and to observe the difference in the levels of damage to liver and kidney functions in children with and without dental fluorosis in an area having the same level of drinking water fluoride.

Inclusion Criteria:

Selected children living in selected areas of the Henan Province of China.

Exclusion Criteria:

Not specified.

Description of Study Protocol:

Recruitment

Subjects were recruited based on the drinking water fluoride level and dental fluorosis status of their residential area.

Design

Six groups for study were developed based on the amount of fluoride in the drinking water and the existence of fluorosis:
- L1: Low level of fluoride in drinking water (1.1 to 2.0mg per L) without fluorosis
- L2: Low level with fluorosis (41.15%)
- M1: Medium level in water (2.15 to 2.96mg per L) without fluorosis
- M2: Medium level with fluorosis (79.25%)
- H1: High level in water (3.1 to 5.69mg per L) without fluorosis
- H2: High level in water with fluorosis (93.68%)
Fluoride concentration assessed by fluoride ion selective electrode was used to assess concentrations in water, urine and serum
Fluorosis assessed by clinic doctors
Fasting, morning blood and urine samples were collected from each child for analysis
Control group developed from healthy children without dental fluorosis who were living in the area with the drinking water fluoride ranging from 0.61 to 0.87mg per L
Study groups were divided based on water fluoride concentration and existence of fluorosis and assessed for effect on urine and serum concentrations as well as total protein (TP), albumin (ALB), aspartate transamine (AST), alanine transamine (ALT), serum lactic dehydrogenase (LDH), urine N-acetyl-ß-glucosaminidase (NAG) and urine y-glutamyl transpeptidase (y-GT).

Statistical Analysis

Continuous data was presented using mean ± standard deviation
Statistical significance assessed using ANOVA and Dunnett's test (P<0.05).

Data Collection Summary:

Independent Variables

Amount of fluoride in the drinking water: 0.61 to 0.87mg per L, 1.1 to 2.0mg per L, 2.15 to 2.96mg per L and 3.1 to 5.69mg per L, respectively
The existence of fluorosis: 15.23%, 41.15%, 79.25% and 93.68%, respectively.

Dependent Variables

Dose effect response to fluoride exposure with and without fluorosis as measured by:
- Urine fluoride
- Serum fluoride
Effect of fluoride exposure on liver function as measured by:
- Total protein (TP)
- Albumin (ALB)
- Aspartate transamine (AST)
- Alanine transamine (ALT)
- Serum lactic dehydrogenase (LDH)
Effect of fluoride exposure on kidney function as measured by:
- Urine N-acetyl- ß-glucosaminidase (NAG)
- Urine y-glutamyl transpeptidase (y-GT)

Controlled Variables

The effect of fluoride exposure at lower rates in children without fluorosis were used as the controls for comparison as the lowest exposure group (0.61 to 0.87mg per L) with the least chance for impact on laboratory values due to fluorosis.

Timing of Measurements

After assessment of water supply fluoride concentration and individual assessment of fluorosis, blood and urine samples were take from each subject as a morning, fasting sample, one-time measurement.

Description of Actual Data Sample:

Initial N: 210 children, sex not specified
Attrition (final N): Zero; however, children in the lowest fluoride water concentration with fluorosis were not included in the samples discussed (those without fluorosis served as the controls)
Age: 10 to 12 years
Ethnicity: All from Henan Province, China.

Summary of Results:

Dose Effect Response and Relation to Fluorosis

Fluoride levels in the serum and urine were significantly higher in children without and with dental fluorosis in residential areas with high drinking water fluoride compared to controls (P<0.05 for L2 and M1 Urine, L1 and L2 Serum), (P<0.01 for L1, M2, H1, H2 Urine and M1, M2, H1, H2 Serum)
The levels increased gradually as drinking water fluoride levels increased. In area of water fluoride concentration greater than 3.0mg per L, urine fluoride levels increased in children with dental fluorosis significantly more than those without (P<0.05 for serum H2 to serum M1)(P<0.01 for urine L1, M2, H1 and H2 compared to control and for H2 compared to L1, L2, M1, M2 and H1) (P<0.01 for serum M1, M2, H1 and H2 to control; M2, H1, H2 to L1 and L2; and H2 to M1).

Effect of Fluoride Exposure on Liver Function

No significant differences in serum levels of total protein (TP) and albumin (ALB) among groups in high fluoride levels compared to controls
No differences in the levels of serum alanine transaminase (ALT) and aspartate transaminases (AST) activity were observed
Serum lactic dehydrogenase (LDH) activity was higher than control for medium with fluorosis (M2) and all high concentration water groups (H1, H2); (P<0.01 for M2 and H1 to Control, L1, L2, and M1; for H2 to Control, L1, L2, M1, M2 and H1).

Kidney

Urine N-acetyl-ß-glucosaminidase (NAG) activity was significantly higher than control for medium with fluorosis and all high-concentration water groups (P<0.05 for M2, H1 and H2 compared to controls; for M2 and H1 compared to L1 and additionally for H2 compared to L2 and M1) (P<0.01 for H2 to L1)
Urine y-glutamyl transpeptidase (y-GT) activity was higher in M2, H1 and H2 (P<0.05 for M2 compared to control and L2) (P<0.01 for H1 and H2 compared to control, L1, L2, M1 and M2).

The Table below indicates the actual data for assessed values for each of the groups discussed.

Areas involved in significant findings are in bold (P<0.05).

Variables	CONTROL 0.61-0.87mg per L (No Fluorosis Subjects Reported Only)	LOW 1.1-2.0mg per L L1 / L2 (41.15%)	MEDIUM 2.15-2.96mg per L M1 / M2 (79.25%)	HIGH 3.1-5.69mg per L H1 / H2 (93.68%)
Urine fluoride (mg per L)	1.10±0.40	1.98±0.71 / 1.96±1.22	1.95±0.83 / 2.49±1.12	2.56±1.08 / 3.21±1.62
Serum fluoride (mg per L)	0.16±0.06	0.19±0.06 / 0.21±0.03	0.22±0.04 / 0.25±0.04	0.25±0.04 / 0.26±0.03
Total protein (g per L)	72.42±14.37	72.24±14.18 / 76.25±16.53	67.58±12.56 / 72.24±13.43	79.77±14.45 / 79.03±17.30
Albumin (g per L)	39.69±6.43	39.08±9.55 / 41.78±9.36	34.68±9.56 / 38.09±6.26	39.00±7.27 / 41.32±6.93
ALT (U per L)	11.61±5.97	14.74±7.19 / 14.06±4.85	14.19±3.53 / 14.58±4.93	14.43±4.11 / 14.34±3.86
AST (U per L)	28.86±9.85	26.11±9.92 / 33.21±7.42	31.26±6.93 / 32.02±9.15	27.79±7.96 / 28.99±8.33
LDH (U per L)	105.81±10.35	107.80±9.66 / 114.42±14.41	113.44±13.87 / 144.57±26.72	153.55±19.36 / 174.15±30.12
NAG (U per mmol Cr)	1.38±0.36	1.40±0.59 / 1.41±0.60	1.42±0.50 / 1.82±1.00	1.83±0.67 / 1.91±0.88
y-GT (U per mmol Cr)	12.42±3.81	13.00±4.33 / 12.08±2.37	13.40±4.03 / 15.06±3.35	24.81±4.34 / 27.41±8.00

Groups divided by water fluoride content, L= Low, M= Medium, H= High and then by fluorosis: 1=No Fluorosis, 2=Fluorosis (percentage subjects within water group with fluorosis).

Author Conclusion:

In summary, our results suggest that drinking water fluoride levels over 2.0mg per L can cause damage to liver and kidney functions in children and that the dental fluorosis was independent of damage to the liver but not the kidney.

Funding Source:

Government:

National Nature Science Foundation of China and the China National Key Basic Research and Development Program

Reviewer Comments:

Strengths:
- Varied levels of water fluoride concentrations studied
- Includes consideration for impact of fluorosis
Weaknesses:
- Other characteristics of subjects are not described
- Study protocols, laboratory analysis and research incentive in China are not well known.

Quality Criteria Checklist: Primary Research
Relevance Questions
	1.	Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies)	N/A
	2.	Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about?	Yes
	3.	Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice?	Yes
	4.	Is the intervention or procedure feasible? (NA for some epidemiological studies)	N/A

Validity Questions
1.	Was the research question clearly stated?		Yes
	1.1.	Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified?	Yes
	1.2.	Was (were) the outcome(s) [dependent variable(s)] clearly indicated?	Yes
	1.3.	Were the target population and setting specified?	Yes
2.	Was the selection of study subjects/patients free from bias?		No
	2.1.	Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study?	No
	2.2.	Were criteria applied equally to all study groups?	No
	2.3.	Were health, demographics, and other characteristics of subjects described?	No
	2.4.	Were the subjects/patients a representative sample of the relevant population?	No
3.	Were study groups comparable?		No
	3.1.	Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT)	No
	3.2.	Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?	Yes
	3.3.	Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.)	Yes
	3.4.	If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis?	No
	3.5.	If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.)	No
	3.6.	If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")?	N/A
4.	Was method of handling withdrawals described?		Yes
	4.1.	Were follow-up methods described and the same for all groups?	N/A
	4.2.	Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.)	N/A
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	Yes
	4.4.	Were reasons for withdrawals similar across groups?	N/A
	4.5.	If diagnostic test, was decision to perform reference test not dependent on results of test under study?	N/A
5.	Was blinding used to prevent introduction of bias?		Yes
	5.1.	In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate?	N/A
	5.2.	Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.)	Yes
	5.3.	In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded?	Yes
	5.4.	In case control study, was case definition explicit and case ascertainment not influenced by exposure status?	N/A
	5.5.	In diagnostic study, were test results blinded to patient history and other test results?	N/A
6.	Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described?		Yes
	6.1.	In RCT or other intervention trial, were protocols described for all regimens studied?	N/A
	6.2.	In observational study, were interventions, study settings, and clinicians/provider described?	No
	6.3.	Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect?	Yes
	6.4.	Was the amount of exposure and, if relevant, subject/patient compliance measured?	No
	6.5.	Were co-interventions (e.g., ancillary treatments, other therapies) described?	N/A
	6.6.	Were extra or unplanned treatments described?	N/A
	6.7.	Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups?	Yes
	6.8.	In diagnostic study, were details of test administration and replication sufficient?	N/A
7.	Were outcomes clearly defined and the measurements valid and reliable?		Yes
	7.1.	Were primary and secondary endpoints described and relevant to the question?	Yes
	7.2.	Were nutrition measures appropriate to question and outcomes of concern?	Yes
	7.3.	Was the period of follow-up long enough for important outcome(s) to occur?	N/A
	7.4.	Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures?	Yes
	7.5.	Was the measurement of effect at an appropriate level of precision?	Yes
	7.6.	Were other factors accounted for (measured) that could affect outcomes?	No
	7.7.	Were the measurements conducted consistently across groups?	Yes
8.	Was the statistical analysis appropriate for the study design and type of outcome indicators?		Yes
	8.1.	Were statistical analyses adequately described and the results reported appropriately?	Yes
	8.2.	Were correct statistical tests used and assumptions of test not violated?	Yes
	8.3.	Were statistics reported with levels of significance and/or confidence intervals?	Yes
	8.4.	Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)?	N/A
	8.5.	Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)?	No
	8.6.	Was clinical significance as well as statistical significance reported?	Yes
	8.7.	If negative findings, was a power calculation reported to address type 2 error?	No
9.	Are conclusions supported by results with biases and limitations taken into consideration?		Yes
	9.1.	Is there a discussion of findings?	Yes
	9.2.	Are biases and study limitations identified and discussed?	No
10.	Is bias due to study's funding or sponsorship unlikely?		Yes
	10.1.	Were sources of funding and investigators' affiliations described?	Yes
	10.2.	Was the study free from apparent conflict of interest?	Yes