FL: Fluoride and the Brain (2010)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To examine the association between fluoride intake and intelligence in children.

Inclusion Criteria:
  • 10-12 years old
  • Attendance at school in the Tianjin Xiquing District in China
  • Life-long residents of two villages either with high-fluoride water (3.15±0.61mg/L fluoride) or low-fluoride water (0.37±0.04mg/L fluoride).
Exclusion Criteria:

Pre-existing congenital or acquired neurological disorders.

Description of Study Protocol:

Recruitment

Random cluster sampling method

Design

Cross-sectional study

Blinding used

NA

Intervention

NA

Statistical Analysis

Fisher's exact test, Welch's alternate T-test, rank sum test, multiple regression

 

Data Collection Summary:

Timing of Measurements

Not specified; assume measurements were done in a single visit.

Dependent Variables

Intelligence Quotient (IQ), measured using the Chinese Combined Raven's Test (CTR-C2).  Subjects were categorized into seven groups: Less than 70 retarded, 70-79 borderline, 80-89 dull normal, 90-109 average, 110-119 bright normal, 120-129 superior, and greater than 129, very superior.

Independent Variables

  • Urinary fluoride levels, measured using a fluoride ion selective electrode
  • Water fluoride levels, measured using a fluoride ion selective electrode.

Control Variables

Past history of illness, age, sex, residential history, parents' past history of illness, parents' social status, parents' economic status, parents' education level, parents' income, parents' smoking and parents' use of alcohol.

 

Description of Actual Data Sample:

 

Initial N

118

Attrition (final N)

118

Age

Not reported

Ethnicity

Chinese

Other relevant demographics

Not reported, but authors stated that children from high- and low-fluoride water areas were not different in social, educational and economic backgrounds.

Anthropometrics

Not reported

Location

China

 

Summary of Results:

 

Urinary fluoride levels and IQs of children living in high- and low-fluoride water areas

Fluoride content in drinking water

Number of children

Urinary fluoride level (mean ± SD, mg/L)

IQ level
(mean ± SD)

High (3.15±0.61mg/L)

60

4.99±2.57

P<0.0001

92.27±20.45

P<0.005

Low (0.37±0.04mg/L)

58

1.43±0.64

103.05±13.86

 

Distribution of IQ scores for children living in high- and low-fluoride water areas (number of children, percentage)

Fluoride content in drinking water

IQ<70
Retarded*

IQ 70-79
Borderline*

IQ
80-89
Dull Normal

IQ
90-109
Normal

IQ
110-119
Bright Normal

IQ
120-129
Superior

IQ >129
Very Superior

High

5, 8.3%

8, 13.3%

12, 20.0%

26, 43.3%

5, 8.3%

3, 5.0%

1, 1.7%

Low

0, 0%

2, 3.4%

6, 10.3%

30, 51.7%

13, 22.4%

5, 8.6%

2, 3.4%

 *significantly different between two groups

  • Mean urinary fluoride was significantly higher among children in high-fluoride water area than children in low-fluoride water area (P<0.0001)
  • Children living in the high-fluoride water area had significantly lower mean IQs than children in low-fluoride water area (P<0.005)
  • Proportion of children categorized as retarded or borderline was significantly higher among children in high-fluoride water area than children in low-fluoride water area (P<0.0005)
  • Urinary fluoride level significantly inversely associated with IQ in multiple regression analysis (multiple regression coefficient R=0.3172, P<0.01).

 

 

Author Conclusion:

Children exposed to high levels of fluoride may be at risk for impaired development of intelligence.

Funding Source:
Other: Funding source was not reported
Reviewer Comments:
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) Yes
  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) Yes
 
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? Yes
  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? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  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? Yes
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? ???
  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? ???
  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.) ???
  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? No
  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%.) No
  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? No
  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.) No
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? No
  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? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.6. Were extra or unplanned treatments described? No
  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? Yes
  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? Yes
  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? N/A
  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)? Yes
  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? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? No
  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? No
  10.1. Were sources of funding and investigators' affiliations described? No
  10.2. Was the study free from apparent conflict of interest? ???