FL: Fluoride and the Brain (2010)
Citation:
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To present a meta-analysis to answer the following questions:
- Is there truly an association between low IQ and fluoride in China over the past 20 years?
- How strong is the association?
Inclusion Criteria:
Literature Search of MEDLINE, SCI and CNKI for articles that were published with these criteria:
- English or Chinese language
- 1988 to 2008
- Keywords: Fluorosis, fluoride, intelligence, IQ.
Additional articles found via website www.fluorideresearch.org, restricting to China.
Exclusion Criteria:
26 studies were excluded due to any of the following:
- Not enough data to include in meta-analysis
- Published more than once (i.e., in both English and Chinese and therefore already included).
Description of Study Protocol:
Recruitment
Literature review
- MEDLINE, SCI, CNKI, www.fluorideresearch.org
- English or Chinese language
- 1988 to 2008
- Keywords: Fluorosis, fluoride, intelligence, IQ.
Design
Meta-analysis.
Blinding Used
Not applicable.
Intervention
Not applicable.
Statistical Analysis
Meta-analysis for summary weighted mean difference (WMD) and 95% confidence intervals (CI)
- Mantel-Haenszel method to estimate the summary WMD and its standard error
- DerSimonian-Laird method to estimate the summary WMD and its standard error. No test of homogeneity is available for this method.
Sensitivity Analysis
Funnel plot for bias analysis.
Data Collection Summary:
Timing of Measurements
One-time meta-analysis of research conducted over 20-year period, 1988 to 2008.
Dependent Variable
IQ (mean±SD).
Independent Variables
- Fluorosis (severe, medium, slight) area
- Non-fluorosis area.
Control Variables
Not stated.
Description of Actual Data Sample:
- Initial N: 16 studies (1992 to 2008); 6,221 people (1,673 in non-fluorosis areas)
- Attrition: None
- Age: Children (age not specified)
- Ethnicity: Chinese (per specifications of internet search)
- Other relevant demographics: Not specified
- Anthropometrics: Not specified
- Location: China.
Summary of Results:
- The risk of developing low IQ ranged from a low of 0.2 ("slight fluorosis area") to a high of 10.78 ("severe fluorosis area"). 12 studies found significant increased risk of low IQ due to fluorosis.
- Summary WMD calculated via Mantel Haenszel method was -4.97 (95% CI, 5.58 to -4.36; P<0.01), although this may be invalid due to lack of homogeneity of studies
- Summary WMD per DerSimonian-Laird method was -5.03 (-6.51 to -3.55; P<0.01), preferred due to random effects model
- Sensitivity analysis indicated results as "reliable" and "believable"
- Funnel plot for bias analysis indicates bias, due to publication and language.
Author Conclusion:
Children who live in a fluorosis area have five times higher odds of developing low IQ than those who live in a non-fluorosis area or a slight fluorosis area.
Funding Source:
| University/Hospital: | Nanjing University School of Medicine, Nanjing Jinling Hospital, China |
| Other: | unreported |
Reviewer Comments:
Strength
Clearly-defined parameters for literature review over a 20-year period.
Weaknesses
- Funding source not specified
- Studies combined despite homogeneity questioned
- Levels of fluoride exposure not quantified, thus we cannot tell what "slight," "medium" or "severe" levels of exposure mean. This hampers the ability to apply this research to other contexts.
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Quality Criteria Checklist: Review Articles
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| Relevance Questions | |||
| 1. | Will the answer if true, have a direct bearing on the health of patients? | Yes | |
| 2. | Is the outcome or topic something that patients/clients/population groups would care about? | Yes | |
| 3. | Is the problem addressed in the review one that is relevant to dietetics practice? | Yes | |
| 4. | Will the information, if true, require a change in practice? | Yes | |
| Validity Questions | |||
| 1. | Was the question for the review clearly focused and appropriate? | Yes | |
| 2. | Was the search strategy used to locate relevant studies comprehensive? Were the databases searched and the search termsused described? | Yes | |
| 3. | Were explicit methods used to select studies to include in the review? Were inclusion/exclusion criteria specified andappropriate? Wereselectionmethods unbiased? | Yes | |
| 4. | Was there an appraisal of the quality and validity of studies included in the review? Were appraisal methodsspecified,appropriate, andreproducible? | No | |
| 5. | Were specific treatments/interventions/exposures described? Were treatments similar enough to be combined? | No | |
| 6. | Was the outcome of interest clearly indicated? Were other potential harms and benefits considered? | Yes | |
| 7. | Were processes for data abstraction, synthesis, and analysis described? Were they applied consistently acrossstudies and groups? Was thereappropriate use of qualitative and/or quantitative synthesis? Was variation in findings among studies analyzed? Were heterogeneity issued considered? If data from studies were aggregated for meta-analysis, was the procedure described? | Yes | |
| 8. | Are the results clearly presented in narrative and/or quantitative terms? If summary statistics are used, are levels ofsignificance and/or confidence intervals included? | Yes | |
| 9. | Are conclusions supported by results with biases and limitations taken into consideration? Are limitations ofthe review identified anddiscussed? | No | |
| 10. | Was bias due to the review's funding or sponsorship unlikely? | ??? | |