Effect of high water fluoride concentration on the intellectual development of children in Makoo/Iran.

OBJECTIVE: Prolonged excessive intake of fluoride during child’s growth and development stages has been associated with mental and physical problems. The aim of this study was to investigate the effect of excessive fluoride intake on the intelligence quotient (IQ) of children living in five rural areas in Makoo/Iran.

MATERIALS AND METHODS: In this cross-sectional study, 293 children aged 6-11 years were selected from five villages in Makoo with normal fluoride (0.8±0.3 ppm), medium fluoride (3.1±0.9 ppm) and high fluoride (5.2±1.1 ppm) in their water supplies. The IQ of each child was measured by the Raven’s test. Educational and residential information and the medical history of each child was recorded by a questionnaire completed by the parents. Data were analyzed by ANOVA test with a significance level of 0.05.

RESULTS: The mean IQ scores decreased from 97.77±18.91 for the normal fluoride group to 89.03±12.99 for the medium fluoride group and to 88.58±16.01 for the high fluoride group (P=0.001).

CONCLUSION: Children residing in areas with higher than normal water fluoride levels demonstrated more impaired development of intelligence. Thus, children’s intelligence may be affected by high water fluoride levels.

EXCERPTS:

Study population:

Two-hundred ninety-three participants (142 boys and 151 girls) out of 314 children (6-11 year olds) living in five villages in Makoo were recruited for the study. The five selected rural areas were similar in their general demographic and geographic characteristics with the inhabitants having a comparable level of socioeconomic status and similar occupations. As fluoride excess toxicity is increased by iodine deficiency [7], we measured the amount of iodine in their drinking water and made sure that all households received iodine enriched salts for cooking and eating purposes.The villages (Babur, Panjarlu, Dizaj, Small Donalau and Large Donalau) were classified into three groups based on the fluoride content of their water supplies (normal, medium and high). According to WHO guidelines, the standard range for water fluoride concentration is 0.5-1 mgL-1 and levels greater than that were classified as medium (3.1±0.9 ppm) and high (5.2±1.1 ppm) [1, 14, 21]. All participants were long-life residents of the villages under study, with their mothers having lived in the area during their pregnancies. The exclusion criteria included a history of genetic disease, systemic disorders or brain trauma in the family.

A written informed consent was obtained from the parents of all eligible subjects after explaining the nature and aim of the study. A detailed questionnaire was completed with the assistance of parents, including information about child’s and parents’ medical and residential history, their educational level and source of drinking water.

Dental examinations:

Following theoretical training for fluorosis, the examiner supervised by an experienced pedodontist examined 40 children who had been selected from the subjects previously. The examiner recorded the diagnosis about each child. If there was any doubt about the diagnosis, a decision was made after discussion. Four weeks later the examined subjects were reexamined in order to assess the intra-examiner reliability. The dental examinations were carried out by a dentist according to the WHO- recommended Dean’s index [1]. Following theoretical training for fluorosis, the examiner supervised by an experienced pedodontist examined 40 children who had been selected from the subjects previously. The examiner recorded the diagnosis about each child. If there was any doubt about the diagnosis,a decision was made after discussion. Four weeks later the examined subjects were reexamined in order to assess the intraexaminer reliability. All dental examinations were performed in the school’s medical room using a mirror and cotton rolls under day light.

IQ evaluation:

The intellectual ability of each child was calculated using Raven’s Color Progressive Matrices (RCPM). The RCPM is a non verbal multiple choice IQ test designed for 5 to 11- year-old children. The models were presented in the form of matrixes. In each test item, the child was asked to identify the missing part that completes the model. The test was administrated in a convenient school classroom under the supervision of a trained psychologist, a teacher and an assistant in a blind manner, following the procedures laid down in the manual of Raven’s Progressive Matrices [22]. The average time taken to complete the test was 30 minutes. The test comprised of 30 problems, beginning with easy problems and ending with difficult ones. Each question contained a matrix of geometric design with eight alternatives for one removed cell. Only one of the options fitted correctly. Each group consisted of 15 students, who worked independently. The children’s IQ scores were divided according to the Stanford-Binet classification in eight groups: Genius (164 and over), very superior (148-164), superior (132-148), above average (116-132), average (84-116), dullness (68-84), borderline (52-68) and mental deficiency (below 58)[23].

RESULT

The villages were classified as normal, medium and high fluoride content according to their water fluoride concentrations. The mean level of fluoride in medium and high groups was approximately 3 and 5 times higher than WHO standards, respectively [1]. A concentration of 0.08-0.1 mg/l for iodine and 0-0.5 mg/l for lead was found by the water content analysis. Two hundred and ninety three 6 to 11-year-old children 6 to 11 took part in this study. Kappa coefficient for intra- examiner reliability was acceptable (0.92). Dental examination revealed that all children in medium and high-fluoride groups demonstrated mild to severe fluorosis. In comparison, only 22% of the subjects in the normal group showed very mild and mild fluorosis and the remaining 78% were unaffected (Table 1). An increase in water fluoride content above the standard level was associated with the incidence of more severe dental fluorosis (P<0.001). IQ evaluation results from the three groups are shown in table 2. Although IQ scores for children with normal fluoride content were significantly higher than the medium and high fluoride level (P=0.001), there was no statistically significant difference between the IQ of children residing in medium and high fluoridated areas (P=0.995). Furthermore, we did not observe any significant difference between
the scores of girls and boys in any of the groups examined (P=0.07). IQ scores of children living in areas with various water fluoride content (normal, medium and high) have been demonstrated in table 3, exhibiting that nearly half of the children residing in the normal fluoride area showed normal IQ levels…

CONCLUSION

Within the limitation of this cross-sectional study, these conclusions may be drawn:

1. The IQ scores of children living in areas with above the standard water fluoride levels were lower compared to children living in normal fluoride level regions.

2. The proportion of children with above the normal intelligence in the group with the standard level of fluoride in their drinking water was greater than those with medium and high fluoride content.

3. Age, gender, child’s and parent’s educational level had no significant impact on the IQ scores.

REFERENCES

1- Fawell J, Baily K, Chilton J, Dahi E, Fewtrell L, Magara Y. Fluoride in drinking water. 1st ed. London: WHO; 2006. p. 1-95.

2- Chandra S, Thergaonkar VP, Sharma R. water quality and dental fluorosis. Indian J Public Health.1981 Jan Mar;25(1):47-51.

3- Neenan ME, Easley M, Ruiz M. Water Fluoridation. In: Harris NO, Garcia-Godoy F. Primary Preventive Dentistry. 6th Ed. New Jersey: Pearson Prentice Hall; 2004. p. 181-239.

4- McDonald RE, Avery D, Stookey GK, Chin JR, Kowolik JO. Dental caries in the child and adolescent. In: McDonald RE, Avery D, Dean J. Dentistry for the child and adolescent. 9th ed. Philadelphia: CV Mosby Co; 2011. p. 177- 204.

5- Susheela AK, Bhatnagar M, Vig K, Mondal NK. Excess fluoride ingestion and thyroid hormone derangements in children living in Dehli, India. Flouride. 2005;38:98-108.

6- Xu H, Jin XQ, Jing L, Li GS. Effect of sodium fluoride on the expression of bcl-2 family and osteopontin in rat renal tubular cells. Biol Trace Elem Res. 2006 Jan:109(1):55-60.

7- Yaming G, Hongmei N, Cuiping F, Hongwei W,Xiaoyan Y, Shaolin W et al. Apoptosis in brain cells of offspring rats exposed to high fluoride and low iodine. Fluoride. 2006:39:173-8.

8- Vani ML, Reddy KP. Effects of fluoride accumulation on some enzymes of brain and gastrocnemius muscle of mice. Flouride. 2000;33:17-26.

9- Mullenix PJ, Denbesten PK, Shunior A, Kernas WJ. Neurotoxicity of sodium fluoride in rats. Neurotoxicol Teratol. 1995 Mar-Apr;17(2):169-77.

10- Chirumari K, Reddy PK. Dose dependent effects of fluoride on neurochemical milieu in hypocampus and neocrtex of rat brain. Fluoride. 2007;40:101-10.

11- Niu R, Sun Z, Cheng Z, Liu H, Chen H, Wang J. Effects of fluoride and lead on nmethyle-d-aspartat receptor 1 expression in the hypocampus of offspring ratpups.Fluoride.2008;41:101-10.

12- Li Y, Jing X, Chen D, Lin L, Wang Z. Effects of endemic fluoride poisoning on the intellectual development of children in Baotou. Flouride. 2008;41:161-4.

13- Rocha-Amador D, Navarro ME, Carrizales L, Morales R, Calderon J. Decreased intelligence and exposure to fluoride and arsenic in drinking water. Cad Saude Publica. 2007;23 Suppl 4:S579-87.

14- Hong F, Cao Y, Yang D, Wang H. R search on effects of fluoride on child intellectual development under different environmental conditions. Flouride. 2008;41:156-60.

15- Meenkashi, Garg Vk, Kavita, Renuka, Malik A. Ground water quality in some villages of Hariyana, India: focus on fluoride and fluorosis. J Hazard Mater. 2004 Jan 2:106(1):55- 60.

16- Wang SX, Wang ZH, Cheng XT, Li J, Sang ZP, Zhang XD et al. Arsenic and fluoride exposure in drinking water: children’s IQ and growth in Shanyin county, Shanxi province, China. Environ Health Perspect. 2007

17- Li J, Yao L, Shao QL, Wu CY. Effects of high fluoride level on neonatal neurobehavioral development. Fluoride 2008;41:165-70.

18- Xiang Q, Liang Y, Chen L, Wang C, Chen B, Chen X, Zhou M. Effect of fluoride in drinking water on children’s intelligence. Fluoride. 2003;36:84-94.

19- Shivaprakash PK, Ohri K, Noorani H. Relation between dental fluorosis and intelligence quotient in school children of Bagalkot district. J Indian Soc Pedod Prev Dent. 2011; 29: 117-120.

20- Asghari Moghaddam A, Fijani E. Distribution of fluoride in ground water of Maku area,northwest of Iran. Environ Geol.2008;56:281-7.

21- please find it at: http://www.springer.com/article/10.1007/s00254- 007-1163-2 Briefing on fluoride in drinking
water WHO; Available at: http://www.who.int/oral_health/events/oral%20healtha.pdf. Accessed August 6, 2011.

22- Raven J, Raven JC, Court JH. Manual for Raven’s progressive matrices and vocabulary scales. Oxford, England: Psychologist press/san Antorio; 1998.

23- IQ reference chart. Available at : http://en.wikipedia.org/wiki/IQ_reference_chart. Accessed June 14, 2011.

24- Nowak A, Crall JJ. Prevention Of Dental Disease. In: Pinkham JR, Cassamassimo PS, Mctigue DJ, Fields HW. Pediatric Dentistry Infancy Through Adolescence. 5th ed. St Louis: Elsevier Saunders; 2005. p. 220-35.

25- Ding Y, Gao Y, Sun H, Han H, Wang W, Ji X et al. The relationship between low levels of urine fluoride on children’s intelligence, dental fluorosis in endemic fluorosis areas in Hulunbuir, Inner Mongolia, China. J Hazard Mater. 2011 Feb 28;186(2-3):1942-6.

26- Trivedi MH, Verma RJ, Chinoy NJ, Patel RS, Sathawara NG. Effect of high fluoride water on intelligence of school children in India. Fluoride. 2007;40(3):178-83.

27- Lim KK, Siti Rohana D, Zawiah A, Wan Nazaimoon WM. An evaluation of the effectiveness of water iodinator system to supply iodine to selected schools in Terengganu, Malaysia. Trop Biomed. 2006 Dec;23(2):172-8.

28- Evens E, Ruth A, Osnick J, Yves P. Human health risk assessment of lead in drinking water: a case study from Port-au-Prince, Haiti. Int J Environment Pollution. 2007;31:280-91.

29- Bloylock RL. Excitotoxicity: a possible central mechanism in flouride neurotoxicity. Flouride. 2004;37:301-14.

30-Raven J. The Raven’s progressive matrices: change and stability over culture and time. Cogn Psychol. 2000;41:1-48.

31- Hayashi M, Kato M, Igarashi K, Kashima H. Superior fluid intelligence in children with Asperger’s disorder. Brain Cogn. 2008 Apr;66(33):306-10.

32- Saw SM, Tan SB, Fung D, Chia KS, Koh D, Tan DT et al. IQ and the association with myopia in children. Invest Ophthalmol Vis Sci. 2004 Sep;45(9):2943-8.

33- Seraj B, Shahrabi M, Falahzade M, Falahzade F, Akhondi N. Effect of fluoride concentration in drinking water on children`s intelligence. Journal of dental medicine 2006;19:80-6.

34- Xiang Q, Liang Y. Blood lead of childrenin Wamiao-Xinhuai intelligence study. Fluoride. 2003;36:198-9.