An analysis of the intelligence level of children born in different time periods after iodized salt was supplied in regions with iodine deficiency in Liaoning province

Abstract

objecfive To know and compare the intelligence level of children born in different time periods in regions with iodine deficiency disorders(IDD)in Liaoning province.Methods All 7-14 year-old children from ten schools were chosen as the subjects respectively from six villages in each of the six counties and in regions with iodine deficiency,who were respectively born at the initialization of iodinated salt supplying period(1978-1980);non-iodinated salt supplying period(1981-1990);recovery of supplied iodized salt period(1991-1995);universal iodized salt period(1996-2000),respectively.Intelligence quotient(IQ)was measured by Combined Ravens Test in China(CRT-C)and Combined Ravens Test-the Rural,in China,2nd edition(CRT-RC2).Results IQ of children during the non-iodized salt period(91.9±14.3)was significantly lower than the initial supply of iodized salt period(95.8±14.6,q=8.60,P<0.01),recovery of supplied iodized salt period(99.7±14.7)was significantly higher than the initial supply of iodized salt period, non-iodized salt sales period(q = 9.53, 18.13, all P < 0.01 ),universal salt iodization( 104.3 ± 14.9) was significantly higher than the initial supply of iodized salt period, non-iodized salt sales period, recovery of supplied salt iodization(q = 20.00,28.00,10.46, all P < 0.01). Children's rate of mental retardation (IQ≤69) was higher in non-iodinated salt supplying period (6.7%, 88/1314 ) than the initial supply of iodized salt (4.4%, 21/471, χ2 = 3.85, P < 0.05), recovery of supplied iodized salt period(3.3%,48/1470) was significantly lower than non-iodinzed salt supplying period (χ2 = 15.37, P < 0.01), universal salt iodization period(2.7%, 36/1344) was lower than the initial supply of iodized salt period(χ2 = 4.41, P < 0.05) and non-iodinzed salt supplying period(χ2 = 26.34, P < 0.01 ). The IQ and intelligent retarded rates in children born during the initial years of iodinated salt supplying period were not different. The IQ of the children during ten years of non-iodized salt supplying period fluctuated in a "∪" curve, while the intelligent retardation rates in a "∩" curve.The children born during the period of recovery supplied iodized salt increased their IQ and lowered the retardation rates year after year. The IQ of the children in universal iodized salt period kept on increasing while intelligent retarded rates reduced to the lowest level. Conclusions The intelligence level of children born in regions with IDD during non-iodized salt supplying period is remarkably lower than that of the beginning years of iodinated salt supplying period. The intelligence level of children born after universal iodized salt period is remarkably higher than that of the initial iodinated salt supplying period and recovery of supplied iodized salt period, respectively. Key words: Iodine; Deficiency disease; Children; Intelligence