The Effects of endemic fluoride poisoning caused by coal burning on the physical development and intelligence of children.

Abstract

Study originally in Chinese. Translated by Julian Brooke and published with the permission of the Journal of Applied Clinical Pediatrics 2005;20(9):897-9.
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Goal: To investigate the effects of endemic fluoride poisoning caused by coal burning on the physical development and intellectual ability of children.

Method: Using random sampling from the relevant population, 176 fluorosis sufferers aged 7–12 (the subjects) were drawn from a heavily fluoride poisoned area of Zhijin County, with 50 children without dental fluorosis (the control) selected from a less severely poisoned area. The children were subjected to tests to determine levels of urinary fluoride, physical development, and intellectual ability, followed by analysis of the various measurements.

Results: Compared to the control group, the fluorosis group showed retarded physical development, and the levels of urinary fluoride and intellectual ability were both lower than the control (P < 0.05 for both).

Conclusion: high fluoride burden has a definite effect on the intellectual and physical development of children.

FULL-TEXT (excluding Tables)

INTRODUCTION

Fluoride poisoning is endemic throughout the world. Its prevalence in many parts of China is undisputed, with Guizhou being one of the provinces most seriously affected by the pernicious effects of fluoride poisoning due to the burning of contaminated coal. Guizhou’s Zhijin County is classified as a severely affected, endemic area, and it has been shown that prolonged intake of excess fluoride can damage the central nervous system.1-3 Therefore, in October and November 2004, with the goal of investigating the relationship between high fluoride exposure and intellectual levels as well as physical development, we carried out a study of the physical development and intellectual ability of children from Zhijin County.

SUBJECTS AND METHODS

1. SUBJECTS:

From a zone with severe fluoride poisoning, children aged 7–12 were selected by random sampling, with 57 subjects (33 boys, 24 girls) suffering from skeletal fluorosis and 119 subjects (59 boys, 60 girls) suffering from dental fluorosis alone; 50 subjects (31 boys, 19 girls) were drawn from a zone with relatively low
fluoride. All the subjects were registered students, and both zones were free from iodine deficiency, with the basic conditions, including standard of living, level of medical treatment available, sanitation, and cultural development all essentially the same. Diagnosis of skeletal fluorosis was made according to the standards for
a skeletal fluorosis diagnoses by X-ray (WS192-1999) and child bone X-ray diagnoses.4

2. METHODS:

1. Dental fluorosis: The Dean index as well as the Chinese “3 types, 9 classifications” index was used to identify grade dental fluorosis.

2. X-ray: Two x-rays were taken, one of the pelvis and one of the right crus (when necessary, an x-ray of the tarsus was also taken).

3. Physical tests: Using standard measurement techniques, the height, chest measurement, weight, and abdominal skin thickness of subjects in each group were collected, with the readings accurate to the nearest 0.1 cm, 0.1 kg, and 0.5 mm, respectively. The skin thickness was determined using a Tixing brand skin
thickness meter, calibrated before use, manufactured by the Chinese Physical Culture Administration’s Scientific Research Department.

4. Intelligence testing: The collective testing of intellectual ability was conducted using the Chinese version of the Raven Standard Theoretical Intelligence Text developed by the Psychology Department of Beijing Normal University (the PTCS). For each group of 10 to 20, the test conditions and instructions were kept rigorously uniform as per the requirements of the test. See Table 1 for the criteria used to rank intelligence.

5. Physical development ranking: Based on Chinese reference standards for growth, age-independent height, weight, and chest measurements scores were calculated, and the subjects were classified into five developmental categories: 1) below mean–2SD (low); 2) between mean–2SD and mean–SD (below average);
3) mean±SD (average); 4) between mean+SD and mean+2SD (above average); and 5) above mean+2SD (high).

6. Quality control: The same forms, the same method of questioning, and the same recording system were used for testing, with the same training given to all testers prior to testing; an objective and professional attitude was maintained at all times. In order to be certain that results of the study were both correct and
complete, all results were promptly rechecked, and any problems quickly remedied.

3. STATISTICAL ANALYSIS:

Using the statistical software package SPSS 10.0, the measured data were subjected to a t-test, a variance analysis, and q-test pair-wise comparison, while the categorical data were subjected to a chi-square test and a single factor correlative analysis.
Table 1. Criteria for intelligence rankings Level IQ evaluation standard Rank

RESULTS

1. For the average fluoride level in the urine of Zhijin County children, see Table 2.

2. For the indicators of physical development for children of Zhijin County, see Table 3. The proportions of children in each group with below average height, weight, and chest measurement show no significant differences (P>0.05).

3. For the results of the abdominal skin thickness measuring, see Table 4. The results from the children within the endemic zone showed girls with a statistically significant thicker abdominal skin than boys (P<0.05). Comparing same sex subjects across the three groups, girls show no significant difference (P>0.05); however, the differences among the boys are significant (P<0.05). The two groups from the endemic zone showed no significant differences (P>0.05). The control group had thicker abdominal skin then both the dental fluorosis and skeletal fluorosis groups, and this result was significant (a variance analysis and q-test showed q = 3.46, P <0.05; q = 3.75 P <0.05). The subjects suffering from skeletal fluorosis had lower skin thickness than those with only dental fluorosis, but the difference was not significant (q = 0.23, P>0.05).

4. For the distribution of intelligence rankings for each group of subjects, see Table 5. On the basis of a chi-square test, the difference in IQ between the two zones was found to have statistical significance (chi-square = 23.46, P < 0.01); IQs in the high fluoride zone are clearly lower than the control. Among the 157 students in the endemic zone, three tests were invalid; in the control zone one test was invalid.

5. The relationship between IQs scores and urinary fluoride of children from both zones was investigated by subjecting the urine fluoride and IQ data to a single factor correlative analysis. The results indicate a negative correlation between fluoride in urine and intelligence (r = –0.494, P <0.01)

DISCUSSION

The children from the fluoride endemic areas showed poor development in the growth indicators used in this study, i.e., height, weight, and chest measurement, with height being particularly low. In each group, the percentage of children with below average height was more than 70%, and the children with skeletal fluorosis were on average the shortest. This could be related to the tendency of fluoride to collect in the bones and the resulting damage. Fluoride also seems to be harmful to the muscles, not only causing cells to lose their shape and muscle fibers to lose thickness, but also leading to a general drop in muscle energy metabolism.5 The abdominal skin thickness of the subjects was tested, with the results indicating that
fluoride poisoning has some effect on fat storage, with a corresponding effect on physical development. According to available research, a high body burden of fluoride can inhibit a wide range of enzymes,6 e.g., inhibition of enzymatic hydrolysis of lipids, leading to insufficient amounts of essential fatty acids (linoleic acid, linolenic acid, arachidonic acid, etc.). This could be the cause of the differences in abdominal skin thicknesses seen in this study, but this mechanism needs further research. The difference between the groups suffering from fluorosis and the control with regard to the various physical developmental indicators
(height, weight, chest measurement) seen in this study was not statistically significant; this could be due to the fact that the control group was also drawn from an area that showed some fluoride contamination; they might also have also been, to a certain extent, fluoride poisoned. These indicators also showed no significant differences between the two groups suffering from fluorosis; this indicates that more research into the exact influence of varying degrees of fluoride poisoning on physical development is required.

This study used the PTCS IQ scale to measure intellectual ability, a testing method that minimizes the interference from ethnic, cultural, and linguistic factors. Recent research has demonstrated that excess fluoride uptake can damage the central nervous system, and can pass through the placental and blood-brain
barriers to affect the synthesis and excretion of certain neurotransmitters and thus the various stages of child brain development, causing a retardation in the normal development of the nervous system and ultimately affecting the intellectual ability of the child.7-9 This study found that the children from the severely endemic zone had higher urine fluoride than those from the control zone,b and that urine fluoride and intelligence showed a clear negative correlation, results that are consistentwith the findings of Liu Shusen et al.10-11 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 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.

We also note that our investigation did not discover a clear difference between the intellectual abilities of the two fluorosis groups; this might be related to certain characteristics of brain cell development. These findings also suggest that, given the poisonous nature of fluoride regarding the central nervous system, studying the intellectual ability of children in fluoride endemic areas can better reflect the overall harm that fluoride poses to the heath of children. Of course, fluoride is only one of many factors that influence the physical development and intelligence of children.12,13 Genetics, environment, economics, nutrition, and exercise are also important.14 The region that was investigated in this study was underdeveloped in economic and cultural terms, and the children’s regular diet showed nutrition deficits, including insufficient intake of animal protein, fat, calcium, and vitamins, which could also be playing a role in the retarded physical development of the children. In addition to lowering fluoride intake, other steps such as improving nutrition and increasing physical exercise should be taken to improve the health of children in such areas.

REFERENCES

1 Guan Zhi, Wang Yanan, Gustav D. Changes in the formation of phospholipids inside SH2SY5Y nerve cells caused by fluoride poisoning. Journal of Guizhou Medical College 2004;29(6):471-4.

2 Li Junping, Wang Jundong, Liang Zhanxue, et al. The effects of high fluoride on the central nervous system. Chinese Journal of Veterinary Drugs 2004;38(9):38-47.

3 Xiang Quanyong, Wang Caisheng, Liang Youxin. The poisonous effect of fluoride on the nervous system. Chinese Journal of Endemiology 2005;24(1):114-6.

4 Chen Xuguang, Jiao Juan, Song Anxue, et al. Diagnosis of skeletal fluorosis by x-ray. Journal of Guizhou Medical College 1989;14(3):179-82.

5 Jiang Qingwu. Epidemiology. Beijing: Science Press; 2003. p. 156-8.

6 Zhang Aijun. The effects of fluoride on the endocrine system of organisms. Chinese Journal of Endemiology 1992;7(2):102.

7 Shen Xiuying. The effects of fluoride on the central nervous system. Chinese Journal of Endemiology 2001;16(6):348.

8 Li Yongping, Jin Xiangyi, Chen De, et al. The effects of endemic fluoride poisoning on the intellectual development of children in Baotou. Chinese Journal of Public Health Management 2003;19(4):337-8.

9 Chen Jun, Chen Xuemin. Research on damage to the DNA of brain cells in rats caused by fluoride and the antagonism of fluoride with selenium and zinc. Chinese Journal of Public Health Management 2002;18(7):774-5.

10 Liu Shusen, Lu Yan, Sun Zenrong, et al. Report on the intellectual ability of children living in high fluoride zones. Chinese Journal of Control of Endemic Diseases 2000;15(4):231-2.

11 Wang Sanxiang, Wang Zhenghui, Cheng Xiaotian, et al. Investigation and evaluation of the physical development and intellectual ability of children from areas with endemic arsenic and fluoride poisoning. Chinese Journal of Control of Endemic Diseases 2005;24(2):179-82.

12 Liu Weiming, Tang Jiulai, Wu De, et al. Research on the relationship between the IQ of urban schoolchildren and family background. Journal of Applied Clinical Pediatrics 2004;19(4):308-9.

13 Shi Yanli, Li Lingzheng, Zang Huifang. A longitudinal study of physical and intellectual development in children whose mothers had hypertension during pregnancy. Journal of Applied Clinical Pediatrics
2003;18(10):846-7.

14 Ye Guangjun. Child and Adolescent Health. 5th ed. Beijing: People’s Health Press; 2000. p. 212-4. Editorial comment: The data in Table 2 and in the summary in English in the paper as originally published appear to contradict this statement.

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