FULL-TEXT
Paper: The Relationship of a Low-Iodine and High-Fluoride
Environment to Subclinical Cretinism in Xinjiang
DIRECTORY: Health
/ Brain
/ Fluoride-Iodine Interactions
{See photocopy of original study)
IODINE DEFICIENCY DISORDER NEWSLETTER
August 1991 Vol. 7 No. 3, Pages 24-25
The Relationship of a Low-Iodine and High-Fluoride
Environment to Subclinical Cretinism in Xinjiang
Lin Fa-Fu, Aihaiti, Zhao Hong-Xin, Lin Jin, Jiang Ji-Yong,
Maimaiti, and Aiken.
Xinjiang Institute for Endemic Disease Control and Research;
Office of Leading Group for Endemic Disease Control of Hetian
Prefectural Committee of the Communist Party of China; and
County Health and Epidemic Prevention Station, Yutian, Xinjiang.
Cretinism in iodine-deficiency areas is well known, yet the
milder forms of somatic and psychomotor maldevelopment and
thyroid dysfunction caused by iodine deficiency may be more
difficult to detect. DeQuervain, in 1936, called this milder
form "semi-cretinism," while in 1980 Laggasse used
the term "cretinoidism." It was formally named "subclinical
endemic cretinism" at a symposium on subclinical cretinism
held in Xinzhou, Shanxi province in 1985.
Currently, attention is being focused on these disorders in
China and abroad. The Hetian prefecture in Xinjiang has reportedly
been one of the Asian areas most severely affected by iodine
deficiency disorders (IDD).
During the period 1987-1989, we made a systematic survey of
subclinical endemic cretinism in this district under a UNICEF
aid Project.
Materials and Methods
General conditions and selection of affected areas - The entire
region of Xinjiang in central Eurasia is affected by iodine
deficiency. The study area, located between the southern border
of Tarim basin and the northern slope of Kunlun Mountains,
is arid with sandy soil and an annual precipitation less than
50 mm. The cultivated alluvial plain extends from south to
north with a steepening gradient. The geographical distributions
of endemic goiter and endemic fluorosis are characterized
by marked vertical zones. The inhabitants are of lower socioeconomic
status, with an annual mean income of about 200 yuan (RMB)
per person.
Area with high fluoride and low iodine levels (Area A) - In
the township Xinyuan in the lower reaches of Kliya river in
the county of Yutian, north of the highway, we examined 250
schoolchildren, aged 7-14 years. The goiter prevalence was
91% and dental fluorosis 20.80%. The average level of iodine
in drinking water was 5.21 mg/l, and that of fluoride 0.88
mg/l.
Area with low iodine level (area B) - In the townships of
Langan and Jiayi in the alluvial plain before the mountains
and to the south of the highway, we examined 256 schoolchildren,
aged 7-14 years. The goiter prevalence was 82% and dental
fluorosis of 16.00%. The average water iodine level was 0.96
mg/l and that of fluoride 0.34 mg/l.
Control area with iodine supplementation (Area C) - In the
suburbs of Hetian where the nationalities, habits, customs,
and income were basically similar and where iodine supplementation
in the form of iodized salt or oil has been implemented since
1982, we examined 243 schoolchildren aged 7-14 years.
Methods of Examination
Intelligence test - We used the Combined Raven's Test for
Rural China (CRT-RC). It is culturally fair, non-linguistic,
and particularly suitable for intelligence screening in minorities.
According to the scale, an IQ of 50-69 means mild mental retardation.
Hearing was tested with different frequencies by electroaudiometry
with MST Audiometer (Nagashima Medical Instruments, Co., Ltd.).
Psychiatric-psychological function was tested by the reaction
time tester type XZ-I, knock tester type QJ-I and action stability
tester type WD-Z (Chengde Medical Apparatus and Instruments
Factory), with Ding Zhi-Min's normal values of psychomotilities
as references (2). Bone age was estimated from right palmar
carpal roentgenograms by the method of Li Guo-Zhen (3). Thyroid
131I uptake in 24 hours was determined using automatic scaler
type 126 and GM tube. Thyroid hormones were measured with
kits provided by the Beijing Institute of Atomic Energy.
Methods of epidemiological study - We randomly selected a
class of students in each affected area and examined for endemic
goiter, endemic fluorosis, body height, weight, and intelligence.
Using random stratified sampling method, we examined 10-12
students for hearing, the four psychomotilities, bone age,
thyroid I131 uptake and thyroid hormone. The data obtained
were analyzed by variance and multivariate stepwise regression
with IBM-XT electronic computer.
Results and Analyses
Somatic development of children aged 7-14 in iodine-deficient
areas - The values for weight/height X 100% of 295 children
from the iodine-deficient areas showed a retardation of 1
to 1.5 years compared to those of 1,632 iodine supplemented
children from suburb of Urumqi (p < 0.01). In area A, 29%
showed detectable bone retardation, compared with 13% in area
B and 6% in control area C.
Table 1 shows comparative data for the three areas. Both iodine
deficient areas (A and B) differed from the control area C
by having lower IQ's, higher hearing threshold, increased
131I uptake, higher TSH, and lower urinary iodine. Area A
(high fluoride, low iodine) differed from area B (normal fluoride,
low iodine) by having lower mean IQ, higher TSH, slightly
higher 131I uptake, and higher urinary iodine.
| |
AREA C: Control: Iodine
normal, Fluoride normal (presumed 0.34ppm) |
AREA B: Iodine low
(0.96mg; Fluoride normal (0.34ppm) |
AREA A: Iodine low
(5.21mg; Fluoride "high" (0.88ppm) |
| rT3 |
21ng/dl |
32ng/dl |
58ng/dl |
| rT3/T3 ratio |
N/A |
5.8 |
2.91 |
| Bone retardation |
6% |
13% |
29% |
| Mental retardation |
8% |
16% |
25% |
| Average auditory threshold (dB) |
16 |
20 |
24 |
| Average IQ |
96 |
77 |
71 |
| I131 Uptake(%) |
24 |
50 |
60 |
| TSH (mU/ml) |
6 |
11 |
21 |
Relationships between IQ of children in iodine-deficient areas and
parameters of somatic development, psychomotility and thyroid function
- The relationships of IQs of 130 patients with complete data to
15 factors were studied by correlation analysis and stepwise regression
analysis. Factors closely related to IQ were, in order, age, frequency
of knock, weight/height X 100% and TSH.
Abnormality rates of various parameters of feebleminded children,
aged 7-14 - In children with IQ in the range of 50-69, indices of
all parameters were beyond the normal range. The abnormality rates
of different parameters were, in turn, 74% for ratio of weight/height/age,
59% for TSH, 61% for thyroid I131 uptake, 60% for frequency of mistake,
47% for frequency of knock, and 35% for hearing. In terms of accessory
diagnostic conditions for subclinical cretinism (4), those who met
one item of the conditions accounted for 69% and those who met two
items made up 56%.
Discussion
One hundred and four children with mental retardation were detected
in all. Area A had 25%, area B 16%, and area C 8%. The significant
differences in IQ among these regions suggests that fluoride can
exacerbate central nervous lesions and somatic developmental disturbance
caused by iodine deficiency. This may be in keeping with fluoride's
known ability to cause degenerative changes in central nervous system
cells and to inhibit the activities of many enzymes, including choline
enzymes, causing disturbance of the nerve impulse (5). We found
significant differences among the three areas, indicating that lack
of iodine in children results in disturbance of the process of growth
and ossification and that high fluoride intake can further disturb
bone development (6,7). Also, the auditory threshold was significantly
different among the three areas, with severe loss of hearing in
high fluoride and low iodine areas. Severe iodine deficiency in
early fetal life has adverse effects on the development and differentiation
of the acoustic organ, and we suggest that high fluoride intake
may also promote hearing loss.
In this study, we found that 69% of the children with mental retardation
had elevated TSH levels. IQ and TSH were negatively correlated.
Many investigators regard an elevated TSH in the presence of normal
T4 and T3 levels as evidence for hypothyroidism that is subclinical
but that can still affect the development of brain and cerebral
function to some degree (6). Reverse T3 (rT3) is formed from T4
by 3-deiodination in peripheral tissue. The balance of active T3
and inactive rT3 in the serum reflects thyroid hormone economy.
In high fluoride and low iodine areas, the rT3 value was 58 ng/dl
(the normal value, 21 ng/dl), and the ratio of rT3/T3 was 2.91,
significantly low. In areas of low iodine the rT3 value was 32 ng/dl,
and the ratio of rT3/T3 was 5.8. It is possible that excess fluoride
ion affects normal deiodination.
We detected 104 cases with mental retardation among 769 schoolchildren,
aged 7-14, in different affected areas. Some 69% of our cases with
mental retardation had one or more items of the accessory conditions
recommended for the diagnosis of subclinical cretinism by the National
Conference on Subclinical Cretinism held in Xinzhou (4). According
to the cautious suggestion of Qian Qi-Dong that the diagnosis should
require two or more of the accessory conditions, 56% of our cases
could still be diagnosed as having subclinical cretinism.
Currently, in the vast remote areas of South Xinjiang the control
of IDD with iodized salt has not yet been generally implemented
and the prevalence of subclinical cretinism is still high. This
situation is a great obstacle to the child health, agricultural
development, and economic prosperity of minority nationalities in
South Xinjiang and necessitates prompt implementation of iodine
supplementation to control subclinical cretinism.
Summary
We studied a total of 769 schoolchildren of 7-14 years in three
areas, characterized by intakes of (A) low iodine, high fluoride;
(B) low iodine, normal fluoride; and (C) iodine supplemented, normal
fluoride. Results for the following parameters for areas A, B, and
C, respectively were: (a) average IQ: 71, 77, 96; (b) average auditory
threshold (in dB): 24, 20, 16; (c) bone age retardation (%): 28,
13, 4; (d) thyroid 131I uptake (%): 60, 50, 24; and (e) serum TSH
(mU/ml): 21, 11, 6. Statistically significant differences existed
between these areas, suggesting that a low iodine intake coupled
with high fluoride intake exacerbates the central nervous lesions
and the somatic developmental disturbance of iodine deficiency.
The detection rate of subclinical endemic cretinism in children
with mental retardation was 69%, and the total attack rate of subclinical
endemic cretinism 9%.
References
1.Ma Xin-Yuan, et al . 1987 The study of subclinical endemic cretinism
in Fujian province . Proceedings of the 3rd National Conference
on Endemic Goitre and Endemic Cretinism. Chinese Centre for Endemic
Disease Control and Research, pp 120-125.
2.Ding Zhi-Min. Use of psychomotility function test and exploration
of its normal values. Chinese J of Control of Endemic Diseases 1987;
3:18-20.
3.Li Guo-Zhen, et al . A study of the development of bone: II Percentage
estimation of bone age. Chinese J Rad 1979; 13:19-23.
4.Li Jian-Qun, et al . A Practical Handbook of Prophylaxis and Treatment
of Endemic Goitre and Endemic Cretinism . Chinese Environmental
Science Publishing House, 1987, 1st edition, pp 64-69.
5.Ren Da-Li. An investigation of intelligence development of children
aged 8-14 years in high-fluoride and low-iodine areas. Chinese J
of Control of Endemic Diseases 1989; 4:251.
6.Liu Cheng-Shan, et al. Studies on diagnostic criteria for subclinical
cretinism . Proceedings of the 3rd National Conference on Endemic
Goitre and Endemic Cretinism. Chinese Centre for Endemic Disease
Control and Research, 1987 pp 142-147.
7.Zhang Ying-Xiu. Effect of fluoride on the growth development of
children. Chinese J Endemiology 1989; 4:240.
8.Qian Qi-Dong. Subclinical endemic cretinism. Chinese J Endemiology
1987;6:4-9.
{See photocopy of original study)
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