Fluoride Reduces IQ – 23 published studies

From the Fluoride Action Network

23 published studies report an association of reduced IQ
with high fluoride exposure

Print version (pdf)

In the summer of 2008, the following two reports reviewed the published studies reporting an association of high fluoride exposure and reduced IQ. The fluoride levels in water in these studies range from 0.88 – 9.4 ppm.

Connett M, Limeback H.
Fluoride and its effect on human intelligence. A systematic review.

International Association for Dental Research 83rd General Session and Exhibition. Toronto, Canada.
Poster 2205. July 4, 2008.

Tang Q-Q, Du J, Ma H-H, Jiang S-J, Zhou X-J.
Fluoride and Children’s Intelligence: A Meta-analysis.
Biol Trace Elem Res. 2008 Aug 10. 2008.

The Tang et al. study cites 16 studies, including 5 Chinese studies that had not been translated into English. FAN plans to have them translated.

The Connett & Limeback review, published prior to Tang et al., found 18 out of 20 studies reporting an association to fluoride exposure and lowered IQ. Their results are reproduced below in the following Table.

The citations for the 23 studies are listed at the end with links to the Chinese and translated versions.

The Fluoride journal published 6 of the translated Chinese studies on fluoride’s impact on IQ in its April-June 2008 edition (Qin-1990, Chen-1991, Guo-1991, Liu-2000, Hong-2001, Li-2003) and will publish more translated studies in later editions.

Twelve (12) of the human/IQ studies were originally published in Chinese. Julian Brooke translated these studies into English under contract with Fluoride Action Network.

In their review of the toxicology of fluoride, the committee who authored the 2006 National Research Council of the National Academies report on fluoride (NRC), cited only 3 of the 23 studies in its ‘Findings on Human Cognitive Abilities’, and cited 6 of the 23 studies in its references (Yang et al., 1994; Li et al., 1995; Lin et al., 1991; Zhao et al., 1996; Lu et al., 2000; Xiang et al., 2003). 5 studies (including one untranslated Chinese study) were published after the NRC report was released. The NRC report stated:

Human Cognitive Abilities.
In assessing the potential health effects of fluoride at 2-4 mg/L, the committee found three studies of human populations exposed at those concentrations in drinking water that were useful for informing its assessment of potential neurologic effects. These studies were conducted in different areas of China, where fluoride concentrations ranged from 2.5 to 4 mg/L. Comparisons were made between the IQs of children from those populations with children exposed to lower concentration of fluoride ranging from 0.4 to 1 mg/L. The studies reported that while modal IQ scores were unchanged, the average IQ scores were lower in the more highly exposed children. This was due to fewer children in the high IQ range. While the studies lacked sufficient detail for the committee to fully assess their quality and their relevance to U.S. populations, the consistency of the collective results warrant additional research on the effects of fluoride on intelligence. Investigation of other mental and physiological alterations reported in the case study literature, including mental confusion and lethargy, should also be investigated.
Ref: bottom of page 220 to page 221

The NRC report also stated:

On the basis of information largely derived from histological, chemical, and molecular studies, it is apparent that fluorides have the ability to interfere with the functions of the brain and the body by direct and indirect means. To determine the possible adverse effects of fluoride, additional data from both the experimental and the clinical sciences are needed.
http://www.nap.edu/openbook.php?record_id=11571&page=222

Table from Connett and Limeback 2008 review [comments in italics were not in original paper]
Author
(Year)
Group
compared
Water
[F-]ppm
n Urine
[F-]
IQ test IQ
Results
S.D.
+/-
p Conclusion
Hu
(1989)
Low F
High F
<0.70
>7.0
181
198
ND
ND
84.9
85.15
NR
NR
>0.05 “the effect of fluoride poisoning on intellectual ability is negligible”
Ren
(1989)
Low I
High F, low I
Not
reported
169
160
ND Wechsler 85
64.8
22.3
20.4
<0.01 “Disrupted child intellectual development” is “clearly much more serious” from a “ harmful environment containing both high fluoride and low iodine …than the effects of iodine deficiency alone”
Qin
(1990)
Low F
Normal F
High F
0.1-0.2
0.5-1.0
2.1-4.0
147
59
141
ND
ND
ND
Raven 23.03
28.14
21.17
NR
NR
NR
>0.05
<0.01
“A child whose drinking water is above 2.0 mg/L or below 0.2 mg/L manifest intellectual deficits as compared to ‘normal’ control group.”
Guo
(1991)
Control
Endemic    fluorosis
Serum F
0.10
0.15
61
60
ND
ND
Chinese
Binet
83.95
77.30
8.93
8.52
(7-9 yr.)

<0.05

“children living in high fluoride areas have lower IQs”
Lin
(1991)
Low F, (Low I)
High F (high I)
0.34 (0.96 ppb)
0.88 (5.21 ppb)
256
250
1.52
2.56
78
71
NR
NR
<0.01 “low iodine intake coupled with high fluoride intake exacerbates the central nervous lesions and the somatic developmental disturbance of iodine deficiency”
Chen (1991) Low F
High F
0.89
4.55
320
320
ND
ND
Raven 104.03
100.24
14.96
14.52
<0.01 “fluoride has a direct connection with intellectual development of children”
Yang (1994) Low F (Low I)
High F (high I)
0.5 (0.13 mg/L)
2.97 (1.1 mg/L)
416
1102
0.82
2.03
Chinese Comparative Scale of Intelli-gence Test 81.97
76.67
11.97 7.75 >0.05 IQ ‘somewhat’ lower but not significant

“The average IQ scores of children in the high fluoride, high iodine area and the control area were 76.67±7.75 and 81.67±11.97 respectively. This difference is not significant, however the number of children showing moderately low IQ scores in the subject population is significantly higher than the control. See Table 2.”

Li
(1994)
Low F

HF I no fluorosis
HF II fluorosis
HF III flurosis

0.3 in all water
0.5 ppm (grain)

4.7 ppm (grain)
5.3 ppm (grain)
31.6 ppm(grain)

51

33
37
36

ND
ND

ND
ND
ND

Work capacity
(reaction time, short-term memory, etc.)
Two com-ponents  of mental capacity decreased 0.05
and
<0.01
“early prolonged high fluoride intake causes a decrease an a child’s mental work capacity”
Li
(1995)
Low F
High F
fluorosis

low-mild
severe

226
230
1.02
2.69
Rui Wen 89.9
80.3
10.4
12.9
<0.01 High fluoride environment can adversely affect the development of intelligence in children
Wang (1996) Low F
High F
<1.0
>1.0 – 8.6
83
147
ND
ND
Wechsler 101.23
95.64
15.84
14.34
<0.05 “high fluoride intake has a clear influence on the IQ of preschool children”
Zhao
(1996)
Low F
High F
0.91
4.12
160
160
ND
ND
Pau Wan 105.21
97.69
14.99
13.00
<0.01 “The intake of high fluoride drinking water before birth had a significant deleterious influence on children’s IQ. “
Lu
(2000)
Low F
High F
0.37
3.15
58
60
1.43
4.99
Raven 103.5
92.2
13.86
20.45
<0.005 “exposure of children to high levels of fluoride may therefore carry the risk of impaired development of intelligence”
Hong
(2001)
Low F
High F
High F, low I
0.75
2.90
2.94
32
85
28
ND
ND
ND
Raven 82.79
80.58
68.38
8.98
2.28
19.12
>0.05
<0.01
F makes I-deficiency worse, lowering IQ more than just with low I
Li
(2003)
Non-fluorosis
fluorosis
ND
ND
301
419
ND
ND
Raven 96.97
88.67
18.43
15.26
<0.01 Fluoride disrupts intellectual development
Xiang
(2003)
Low F
High F
0.36
2.47
135
155
1.11
3.47
Combined raven 100.41
92.02
0.003 drinking water fluoride levels greater than 1.0 mg/L may adversely affect the development of children’s intelligence”
Wang
(2005)
Control
dental fluorosis
skeletal fluorosis
49
97
57
1.61

1.35

Raven percentiles
5-25 >75
4
14
24
8
12
2
<0.01 “..Negative correlation between urine fluoride and intelligence”

“…The numbers of below-average IQ subjects from the two fluorosis groups were clearly higher than the control group. Further demonstrating that high fluoride intake has a damaging effect on intellectual ability.  Even the control group had 16.3% of subjects in the low range, suggesting that even moderate levels of fluoride contamination such as were present in the control zone can still have a noticeable effect on the intellectual development of children.”

Seraj
(2007)
Low F
High F
0.4
2.5
85
41
ND
ND
Raven 98.9
87.9
12.9
11.0
0.000 “High F may be associated with impaired development of intelligence”
Rocha-Amador (2007) Low F
Mod F
High F
0.8
5.3
9.4
52
20
60
1.5
6.0
5.5
Wechsler b values
-6.7
-11.2
-10.2
<0.001
<0.001
<0.001
“Children exposed to either F or As have increased risks of reduced IQ scores”
Trivedi
(2007)
Low F
High F
2.01
5.55
101
89
2.30
6.13
Stanford-Binet 100.04
91.72
1.23
1.13
<0.001 “..the mean IQ level of students exposed to high F drinking water was significantly lower than that of the students to a lower F level drinking water”
Wang
(2007)
Low F
High F
0.5
8.3
110
106
1.5
5.1
Raven 105
101
15
16
<0.05 “Children’s intelligence and growth can be affected by high concentrations of As or fluoride.”

For the sources to this table click here