Harvard IQ Study FAQ
CHOI et al., “DEVELOPMENTAL FLUORIDE NEUROTOXICITY:
A SYSTEMATIC REVIEW AND META-ANALYSIS”
Environ Health Perspect. 120(10):1362-8 (2012)
WHO WERE THE RESEARCHERS?
Anna Choi, from the Harvard School of Public Health, was lead author. The other authors were Guifan Sun and Ying Zhang from China Medical University in Shenyang, China and Philippe Grandjean of Harvard and the Institute of Public Health at the University of Southern Denmark
WHO FUNDED THE STUDY?
WHO PUBLISHED THE STUDY?
Environmental Health Perspectives, a highly respected peer-reviewed journal published by the National Institute of Environmental Health Sciences, a division of NIH
WHAT’S A META-ANALYSIS?
A systematic method that takes data from a number of independent studies and integrates them using statistical analysis. (Dorland’s Medical Dictionary for Health Consumers)
WHAT STUDIES DID IT REVIEW?
Twenty-seven studies that examined the effects of fluoride exposure on IQ in children. Twenty-five were in China and two in Iran. The studies were published between 1989 and 2011.
Twenty-one measured fluoride from drinking water, three from coal burning and three from comparing fluorosis rates. Fluorosis, a mottling of the teeth, is caused by excessive fluoride.
WHAT DID IT FIND?
In 26 of 27 studies, children with increased exposure to higher levels of fluoride tested lower for IQ. The weighted average was 7 IQ points, highly statistically significant. In a large population like Seattle, a shift of 5 IQ points would cut the number of geniuses in half and double the number of developmentally disabled.
WERE THE FLUORIDE LEVELS IN THE WATER FOR THE VILLAGES STUDIED HIGHER THAN FLUORIDATION LEVELS FOR US CITIES?
For the most part, yes. Most U.S. cities fluoridate at 0.7 milligrams per liter (mg/L). The villages in the studies that had the high fluoride/lower IQ’s had water levels ranging from .88 mg/L to 11.5 mg/L. Fourteen of the high fluoride/low IQ test villages had levels between 3 mg/L. and 5 mg/L.
SINCE THE LEVELS IN THE HIGH FLUORIDE/LOWER IQ VILLAGES WERE USUALLY HIGHER THAN 0.7 mg/L, DOES THAT MEAN THERE ISN’T A PROBLEM HERE?
No. There is no margin of safety for variations between individuals. Some people, such as those with iodine deficiency, are more susceptible to fluoride’s toxicity than others. Others, such as athletes, manual laborers and those with kidney disease and/or diabetes, typically drink more water. The dose can be just as big of a factor as the level of fluoride.
To take into account these variations when determining a margin of safety for the entire range of a population, toxicologists figure in a factor of at least 10. For example, if children drinking water with a fluoride level of 3 mg/L are showing lower IQ’s, the margin of safety to protect the entire range of a population would be .3 mg/L, lower than the 0.7 mg/L levels of most U.S. fluoridated cities.
There is another major factor that is often neglected. U.S. children in a .7 mg/L area consuming drinks using fluoridated water, eating processed foods with fluoride, taking fluoride supplements, etc. will likely receive as much fluoride as Chinese children drinking water with 2-3 mg/L of fluoride.
Choi noted that “each of the articles reviewed had deficiencies, in some cases rather serious, which limit the conclusions that can be drawn.” Does this make the study invalid? No. Choi also noted “most deficiencies relate to the reporting, where key information is missing.” Most epidemiological studies have weaknesses and none are perfect – it’s virtually impossible to control for every variable when comparing two communities.
One of the main variables can be arsenic, which can lower intelligence. However, many of the individual studies controlled for arsenic and Choi stated that “From the geographical distribution of the studies, it seems unlikely that fluoride-attributed neurotoxicity could be due to other water contaminants.”
Actually, China is a favorable country to carry out these studies, because it has many villages with stable populations of similar socio-economic levels, water supplies and fluoride levels that haven’t varied for many years.
The main point is this: After considering all the variables, the study concluded “our results support the possibility of adverse effects of fluoride exposures on children’s neurodevelopment.” Also, noting the consistency of results of the studies (26 out of 27), the study stated that “potential developmental neurotoxicity of fluoride should be a high research priority.”
ARE THERE ANY OTHER STUDIES THAT HAVE BEEN DONE SINCE CHOI?
Yes, one in India in 2012 and one in China in 2011.
WHAT DID THEY FIND?
The same results – the higher the fluoride exposure, the lower the IQ. Choi commented on the 2011 study (Ding et al), which used a different measurement. It showed the higher the level of fluoride in the urine, the lower the IQ. This individual measurement is even stronger than simply comparing the high and low fluoride villages. Choi said that the Ding study “suggested that low levels of water fluoride (range 0.24 to 2.84 mg/L) had significant negative associations with child’s intelligence.”
HAVE THERE BEEN ANY SIMILAR STUDIES DONE IN THE US?
No, even after the landmark 2006 study done by the National Research Council of the National Academy of Sciences Fluoride in Drinking Water recommended it.
WHAT ABOUT ANIMAL STUDIES?
There have been over 80 animal studies that found fluoride causing harmful effects on memory, learning and behavior. The National Academy of Sciences 2006 report said “it is apparent that fluorides have the ability to interfere with the functions of the brain and the body by direct and indirect means.” Also, “these changes have a bearing on the possibility that fluorides act to increase the risk of developing Alzheimer’s disease.”
WHAT CAN WE CONCLUDE?
Even with all the information cited above, there isn’t 100% proof that fluoridating water at 0.7 mg/L lowers IQs in children. However, there is a wealth of significant compelling data pointing in that direction. The trend has been consistent over 23 years of studies.
In the Sept. 5, 2012 Harvard School of Public Health press release on the study, co-author Philippe Grandjean stated “Fluoride seems to fit in with lead, mercury and other poisons that cause chemical brain drain.”
The consistency of these results in both human and animal studies and the margin of safety factor noted above point to the unequivocal need for further research. On the question of lowering IQs in children, water fluoridation cannot be declared safe beyond a reasonable doubt.