LETTERS COMMUNITY WATER FLUORIDATION AND INTELLIGENCE The recent article on community water fluoridation (CWF) by Broadbent et al.1 states that our meta-analysis of fluoride exposure and IQ deficits2 was based on “selective readings.” We wish to emphasize that we, for the first time, reviewed 27 eligible studies, many of which shared the unique advantage of stable populations with fairly constant exposures throughout the children’s lifetimes. Because the water--fluoride concentrations in the groups with elevated exposure varied between levels similar to those achieved by CWF and up to 10-fold that level, we refrained from attempting to link the average IQ loss of seven points to specific doses. Because our study was misinterpreted in the media, we released a press statement, which concluded: These results do not allow us to make any judgment regarding possible levels of risk at levels of exposure typical for water fluoridation in the US. On the other hand, neither can it be concluded that no risk is present. We therefore recommend further research to clarify what role fluoride exposure levels may play in possible adverse effects on brain development, so that future risk assessments can properly take into regard this possible hazard.3
Letters to the editor referring to a recent Journal article are encouraged up to 3 months after the article's appearance. By submitting a letter to the editor, the author gives permission for its publication in the Journal. Letters should not duplicate material being published or submitted elsewhere. The editors reserve the right to edit and abridge letters and to publish responses. Text is limited to 400 words and 10 references. Submit online at www. editorialmanager.com/ajph for immediate Web posting, or at ajph.edmgr.com for later print publication. Online responses are automatically considered for print publication. Queries should be addressed to the Editor-in-Chief, Mary E. Northridge, PhD, MPH, at [email protected].
Further, to ascertain the validity of previous Chinese reports on fluoride neurotoxicity, we carried out a pilot study in Sichuan.4 Although we examined only 51 children, our results support the notion that cognitive deficits occur at elevated fluoride exposures. Broadbent et al.1 erroneously state that our press release “had to emphasize the fact that [our] research was irrelevant to CWF,”1(p72) and they give no reason why a threshold for developmental neurotoxicity would necessarily be higher than systemic doses associated with CWF. Also, although the authors1 emphasized potential biases in our meta-analysis,2 they downplayed the wide confidence intervals in their own study and the fact that the 10% who had not lived in fluoridated areas likely received fluoride supplements. Other dentistry colleagues5 claim that our work has been severely criticized and conclude that the Broadbent et al. study1 “found that fluoridation is not neurotoxic for either children or adults, and does not have a negative effect on IQ.” We are therefore concerned that the safety of elevated fluoride exposure is being exaggerated in ways similar to those employed by vested interests to misconstrue the scientific evidence of other neurotoxicants, such as lead, mercury, and certain pesticides.6 Firm dismissal of fluoride as a potential neurotoxic hazard would seem premature. j Philippe Grandjean, MD, PhD Anna L. Choi, ScD
About the Authors Philippe Grandjean is with the Department of Environmental Health, Harvard School of Public Health, Boston, MA, and the Department of Environmental Medicine, University of Southern Denmark, Odense. Anna L. Choi is with the Department of Environmental Health, Harvard School of Public Health. Correspondence should be sent to Philippe Grandjean, Professor, Department of Environmental Health, Harvard School of Public Health, 401 Park Drive E3-110, Boston, MA 02215 (e-mail: [email protected]). Reprints can be ordered at http://www.ajph.org by clicking the “Reprints” link. This letter was accepted December 17, 2014. doi:10.2105/AJPH.2014.302532
April 2015, Vol 105, No. 4 | American Journal of Public Health
Contributors The authors contributed equally to this letter.
Acknowledgments The authors declare they have no competing financial interests.
References 1. Broadbent JM, Thomson WM, Ramrakha S, et al. Community water fluoridation and intelligence: prospective study in New Zealand. Am J Public Health. 2015;105(1):72---76. 2. Choi AL, Sun G, Zhang Y, Grandjean P. Developmental fluoride neurotoxicity: a systematic review and meta-analysis. Environ Health Perspect. 2012;120:1362--1368. 3. Choi AL, Grandjean P. Statement on Fluoride Paper: Harvard Press Release. Cambridge, MA: Harvard University; 2012. Available at: http://www.hsph.harvard. edu/news/features/fluoride-childrens-health-grandjeanchoi. Accessed December 19, 2014. 4. Choi AL, Zhang Y, Sun G, et al. Association of lifetime exposure to fluoride and cognitive functions in Chinese children: a pilot study. Neurotoxicol Teratol. 2015;47C:96---101. 5. Allukian M Jr, Wong C. Fluoridation update 2014. J Mass Dent Soc. 2014;63:24---30. 6. Grandjean P. Only One Chance. How Environmental Pollution Impairs Brain Development—and How to Protect the Brains of the Next Generation. New York, NY: Oxford University Press; 2013.
BROADBENT ET AL. RESPOND Grandjean and Choi appear to have misunderstood our sentence about selective readings. The selective readings we referred to were the misinterpretations made in the media and online. Considering the large number of Web sites and news stories still claiming that a “Harvard Study” concluded that “water fluoridation lowers children’s IQ,” further public clarification is needed. The claim of “an average IQ decrement of about seven points” among children with “elevated exposure” is problematic because it does not clarify what level this “elevated exposure” was, or what it was relative to. We note that the average fluoride concentration of the drinking water in the low-fluoride/high-IQ towns included in the meta-analysis by Choi et al.1 was
Letters | e3
LETTERS
About the Authors Jonathan M. Broadbent is with the Department of Oral Rehabilitation, Sir John Walsh Research Institute, Dunedin, New Zealand. W. Murray Thomson is with the Faculty of Dentistry, Sir John Walsh Research Institute. Terrie E. Moffitt is with Duke University, Durham, NC, and the Institute of Psychiatry, Psychology, and Neuroscience, King’s College London, London, UK. Richie Poulton is with the Department of Psychology, University of Otago, Dunedin, New Zealand. Correspondence should be sent to Jonathan M. Broadbent, Sir John Walsh Research Institute, 310 Great King Street, North Dunedin, Dunedin 9016, New Zealand (e-mail [email protected]). Reprints can be ordered at http://www.ajph.org by clicking the “Reprints” link. This letter was accepted February 18, 2015. doi:10.2105/AJPH.2015.302647
12
Fluoride Concentration, ppm
10
8
6
Contributors
4
All authors contributed equally to this letter.
References 1. Choi AL, Sun G, Zhang Y, Grandjean P. Developmental fluoride neurotoxicity: a systematic review and meta-analysis. Environ Health Perspect. 2012;120: 1362---1368.
2
Poureslami et al. 2011
Wang SX et al. 2007
Fan et al. 2007
Wang ZH et al. 2006
Seraj et al. 2006
Xiang et al. 2003
Wang SH et al. 2001
Hong et al. 2001
Lu et al. 2000
Yao et al. 1997
Zhao et al. 1996
Yao et al. 1996
Wang G et al. 1996
Yang et al. 1994
Xu et al. 1994
An et al. 1992
Lin et al. 1991
Chen et al. 1991
0
Study Low fluoride exposure/reference group midpoint
High fluoride exposure group midpoint
Range of fluoride in non-CWF area of Dunedin
Range of fluoride used in NZ CWF programs
Note. CWF = community water fluoridation; NZ = New Zealand.
FIGURE 1—Water fluoride concentration in studies included in meta-analysis by Choi et al. (2012).
within the recommended range for community water fluoridation programs in the 18 studies that considered water fluoride (Figure 1). Grandjean and Choi stated that their results do not allow them to make any judgement one way or another about possible levels of risk at levels of exposure typical for CWF. If they are unable to make any such evaluation, it follows that their research is not relevant to the context of community water fluoridation. In the Dunedin Study cohort, the majority of children who took fluoride tablet supplements did so intermittently and for only a short period of time. We have now estimated
e4 | Letters
average total fluoride intake in our cohort up to age five years, including tablets, toothpastes, and dietary sources. We identified no differences in IQ in childhood or adulthood by total fluoride intake, but we did identify significantly fewer dental caries in both childhood and adulthood among those with higher estimated fluoride intake up to age five years. j
Jonathan M. Broadbent, W. Murray Thomson, Terrie E. Moffitt, Richie Poulton,
PhD PhD PhD PhD
American Journal of Public Health | April 2015, Vol 105, No. 4
Letters to the editor referring to a recent Journal article are encouraged up to 3 months after the article's appearance. By submitting a letter to the editor, the author gives permission for its publication in the Journal. Letters should not duplicate material being published or submitted elsewhere. The editors reserve the right to edit and abridge letters and to publish responses. Text is limited to 400 words and 10 references. Submit online at www. editorialmanager.com/ajph for immediate Web posting, or at ajph.edmgr.com for later print publication. Online responses are automatically considered for print publication. Queries should be addressed to the Editor-in-Chief, Mary E. Northridge, PhD, MPH, at [email protected].
Further, to ascertain the validity of previous Chinese reports on fluoride neurotoxicity, we carried out a pilot study in Sichuan.4 Although we examined only 51 children, our results support the notion that cognitive deficits occur at elevated fluoride exposures. Broadbent et al.1 erroneously state that our press release “had to emphasize the fact that [our] research was irrelevant to CWF,”1(p72) and they give no reason why a threshold for developmental neurotoxicity would necessarily be higher than systemic doses associated with CWF. Also, although the authors1 emphasized potential biases in our meta-analysis,2 they downplayed the wide confidence intervals in their own study and the fact that the 10% who had not lived in fluoridated areas likely received fluoride supplements. Other dentistry colleagues5 claim that our work has been severely criticized and conclude that the Broadbent et al. study1 “found that fluoridation is not neurotoxic for either children or adults, and does not have a negative effect on IQ.” We are therefore concerned that the safety of elevated fluoride exposure is being exaggerated in ways similar to those employed by vested interests to misconstrue the scientific evidence of other neurotoxicants, such as lead, mercury, and certain pesticides.6 Firm dismissal of fluoride as a potential neurotoxic hazard would seem premature. j Philippe Grandjean, MD, PhD Anna L. Choi, ScD
About the Authors Philippe Grandjean is with the Department of Environmental Health, Harvard School of Public Health, Boston, MA, and the Department of Environmental Medicine, University of Southern Denmark, Odense. Anna L. Choi is with the Department of Environmental Health, Harvard School of Public Health. Correspondence should be sent to Philippe Grandjean, Professor, Department of Environmental Health, Harvard School of Public Health, 401 Park Drive E3-110, Boston, MA 02215 (e-mail: [email protected]). Reprints can be ordered at http://www.ajph.org by clicking the “Reprints” link. This letter was accepted December 17, 2014. doi:10.2105/AJPH.2014.302532
April 2015, Vol 105, No. 4 | American Journal of Public Health
Contributors The authors contributed equally to this letter.
Acknowledgments The authors declare they have no competing financial interests.
References 1. Broadbent JM, Thomson WM, Ramrakha S, et al. Community water fluoridation and intelligence: prospective study in New Zealand. Am J Public Health. 2015;105(1):72---76. 2. Choi AL, Sun G, Zhang Y, Grandjean P. Developmental fluoride neurotoxicity: a systematic review and meta-analysis. Environ Health Perspect. 2012;120:1362--1368. 3. Choi AL, Grandjean P. Statement on Fluoride Paper: Harvard Press Release. Cambridge, MA: Harvard University; 2012. Available at: http://www.hsph.harvard. edu/news/features/fluoride-childrens-health-grandjeanchoi. Accessed December 19, 2014. 4. Choi AL, Zhang Y, Sun G, et al. Association of lifetime exposure to fluoride and cognitive functions in Chinese children: a pilot study. Neurotoxicol Teratol. 2015;47C:96---101. 5. Allukian M Jr, Wong C. Fluoridation update 2014. J Mass Dent Soc. 2014;63:24---30. 6. Grandjean P. Only One Chance. How Environmental Pollution Impairs Brain Development—and How to Protect the Brains of the Next Generation. New York, NY: Oxford University Press; 2013.
BROADBENT ET AL. RESPOND Grandjean and Choi appear to have misunderstood our sentence about selective readings. The selective readings we referred to were the misinterpretations made in the media and online. Considering the large number of Web sites and news stories still claiming that a “Harvard Study” concluded that “water fluoridation lowers children’s IQ,” further public clarification is needed. The claim of “an average IQ decrement of about seven points” among children with “elevated exposure” is problematic because it does not clarify what level this “elevated exposure” was, or what it was relative to. We note that the average fluoride concentration of the drinking water in the low-fluoride/high-IQ towns included in the meta-analysis by Choi et al.1 was
Letters | e3
LETTERS
About the Authors Jonathan M. Broadbent is with the Department of Oral Rehabilitation, Sir John Walsh Research Institute, Dunedin, New Zealand. W. Murray Thomson is with the Faculty of Dentistry, Sir John Walsh Research Institute. Terrie E. Moffitt is with Duke University, Durham, NC, and the Institute of Psychiatry, Psychology, and Neuroscience, King’s College London, London, UK. Richie Poulton is with the Department of Psychology, University of Otago, Dunedin, New Zealand. Correspondence should be sent to Jonathan M. Broadbent, Sir John Walsh Research Institute, 310 Great King Street, North Dunedin, Dunedin 9016, New Zealand (e-mail [email protected]). Reprints can be ordered at http://www.ajph.org by clicking the “Reprints” link. This letter was accepted February 18, 2015. doi:10.2105/AJPH.2015.302647
12
Fluoride Concentration, ppm
10
8
6
Contributors
4
All authors contributed equally to this letter.
References 1. Choi AL, Sun G, Zhang Y, Grandjean P. Developmental fluoride neurotoxicity: a systematic review and meta-analysis. Environ Health Perspect. 2012;120: 1362---1368.
2
Poureslami et al. 2011
Wang SX et al. 2007
Fan et al. 2007
Wang ZH et al. 2006
Seraj et al. 2006
Xiang et al. 2003
Wang SH et al. 2001
Hong et al. 2001
Lu et al. 2000
Yao et al. 1997
Zhao et al. 1996
Yao et al. 1996
Wang G et al. 1996
Yang et al. 1994
Xu et al. 1994
An et al. 1992
Lin et al. 1991
Chen et al. 1991
0
Study Low fluoride exposure/reference group midpoint
High fluoride exposure group midpoint
Range of fluoride in non-CWF area of Dunedin
Range of fluoride used in NZ CWF programs
Note. CWF = community water fluoridation; NZ = New Zealand.
FIGURE 1—Water fluoride concentration in studies included in meta-analysis by Choi et al. (2012).
within the recommended range for community water fluoridation programs in the 18 studies that considered water fluoride (Figure 1). Grandjean and Choi stated that their results do not allow them to make any judgement one way or another about possible levels of risk at levels of exposure typical for CWF. If they are unable to make any such evaluation, it follows that their research is not relevant to the context of community water fluoridation. In the Dunedin Study cohort, the majority of children who took fluoride tablet supplements did so intermittently and for only a short period of time. We have now estimated
e4 | Letters
average total fluoride intake in our cohort up to age five years, including tablets, toothpastes, and dietary sources. We identified no differences in IQ in childhood or adulthood by total fluoride intake, but we did identify significantly fewer dental caries in both childhood and adulthood among those with higher estimated fluoride intake up to age five years. j
Jonathan M. Broadbent, W. Murray Thomson, Terrie E. Moffitt, Richie Poulton,
PhD PhD PhD PhD
American Journal of Public Health | April 2015, Vol 105, No. 4
