Follow-up Of 30 Years To Observe The Impact Of Prevention And Treatment Of Iodine Fortification Strategy On Intellectual Development Of Children—Corrected By Flynn Effect

objectiveIodine is a essential element for the synthesis of thyroid hormones and plays an important role in children brain development.Iodine deficiency iodine can cause neurodevelopmental retardation among children and impair their intellectual development.Historically,Baicheng,a county in Aksu Prefecture of Xinjiang has been a serious prevalence of iodine deficiency disorders(IDD).In around 1960,the survey and iodine additive(e.g.salt iodization,intramuscular iodized oil),was implemented.However,Baicheng has rich mines of rock salt.Local residents preferred soil slat anywhere.The coverage of household iodized salt(C-IS)is below the national standards(95%)for a long time.For this reason,the local IDD staff have attempted alternative methods,such as injection or oral iodized oil which might result in iodine excess and infection,and iodized water of soil salt with a special release device which needed to monitor iodine concentration in device and was replaced immediately.Some surveys showed the median urinary iodine concentration(MUIC)among children was below 100ug/L,and the total goiter rate(GR)was above 5%,which did not reached at the international or national standards of control IDD.The results of surveys meant the children still exposed at the risk of iodine deficiency and there was prevalence of IDD.It was not until 2008,with the more stringent mandatory iodized salt policy,including the government’s granting of free iodized salt to poor families,combined with oral iodized oil capsules for special groups such as pregnant and childbearing women,and breastfeeding women,the strategies of control iodine deficiency becomes more effective.Since 2010,C-IS and qualified iodized salt consumption rate has continued to meet the national elimination standards.In 2013,GR achieved the national standards,which mean the control IDD of Baicheng has realized sutainable IDD elimination.We observed the intelligence of schoolchildren of the same age group evaluated by same test(CRT)five times from 1989 to 2018,about 30 years.For observation of iodine fortification on the development of children intelligence,we have to considerthe effects of social,economic,culture,education,and so on.The Flynn effect(FE)referred to those effects between generations,which can be calculated because we have the three norms sample of CRT for rural of the version of 1989,1996 and 2006.On compared with IQ of children before and after 2008,and corrected by FE,the effect of iodine supplementation on children’s intellectual development can be evaluated for more scientificial and accurate the role of iodine supplementation on control IDD.MethodsThe intelligence gain of rural children aged 7-14 years and 8-10 years in different years was calculated by using CRT-RC in 1987,1996 and 2006.From 1989 to 2018,the intellectual development of Uyghur school children aged8-10 in Wushi County,Aksu Prefecture,Xinjiang was observed five times.A total of660 children were selected,including 72 in 1989,94 in 2002,167 in 2006,60 in 2012,and 267 in 2018.CRt-RC was used for intelligence tests,and CRT-RC 1987 edition and rural norm of the same age were used for children’s IQ.Children’s growth period of iodine deficiency exposure(IDG)from the calculation of the fixed number of year for pregnancy to 10 years old,local do multiple iodized salt coverage(C-IS),the average of the children’s goiter rate(GR),and the results of multiple children urinary iodine median(MUIC),according to the "standard of IDD elimination"(GB 16006-2008)and the WHO recommendation,exposing IDG defined as iodine deficiency,not exposed,half exposed three categories.SPSS 24.0 software was used for statistical analysis.One-way ANOVA or T-test(homogeneity of variance)/Welch ANOVA or Mann-Whitney U test(heterogeneity of variance)were used for data conforming to normal distribution,and LSD-t test(homogeneity of variance)/Games-Howell test(heterogeneity of variance)was used for pairwise comparison.Kruskal-allis H test or Mann-Whitney U test were used for data that did not conform to the normal distribution,and Bonferroni method was used to compare the corrected significance level in pairs.P<0.05 was considered statistically significant differrence.Results1.The Flynn effect.FE in children aged 7-14 years was 0.90 points/year in1987-1996 and 0.56 points/year in 1996-2006,with no gender difference(P>0.05).2.5 CRT results in children.In 1989,2002,2006,2012 and 2018,the average IQ of children in baytown area was 81.67,83.26,89.68,98.50 and 103.23 respectively.Except for the difference between 1989 and 2002 and 2012 and 2018,the difference between the other groups was statistically significant(P<0.05).There were statistically significant differences in the low intelligence rate among the groups(P<0.05).Pap comparison showed that there were statistically significant differences between 1989,2006,2012 and 2018,2002,2012 and 2018(P<0.05),and 2006 and2018(P<0.05).Correlation analysis found that IQ was positively correlated with C-IS,but not with MUIC and GR.3.From 1989 to 2006,the intellectual development of children who received non-continuous iodine supplementation increased slowly.After removing the gain from the Flynn effect,IQ did not increase,but decreased.IQ scores for 1989-2006were-9.57 and-6.11,respectively,after FE adjustment,compared with 1989 IQ scores.Between 2006 and 2018,children who received iodized salt supplements showed an increase in IQ after removing the gain from the Flynn effect.The difference between the two tests was 4.38 and 4.67 points compared with the 2006 results.Conclusion1.The Flynn effect about intelligence has been founded exists among Chinese rural children living in areas with adequate iodine nutrition.There was no gender statistic difference in the Flynn effect(P>0.05)besides few 9 to 11 years old groups,and the Flynn effect in children of younger groups were higher than that in children of elderly groups with the significant difference(P<0.05).The Flynn effect value among 7-14 yrs children of CRT-RC in the version of 1987 and 1996,or 1996 and2006,is 0.9 or 0.74.2.In IDD areas,the intellectual development of children was not stable because iodine deficiency among them can not be improved due to intermittent iodine supplementation during their whole growing period.Therefore,the intelligence of children was not improved after collected by the Flynn effect.Moreover,theintelligence among children with adequate iodine supplementation during the most of growth period was significantly improved,and IQ has increase of 4.67 points.3.The results of this study might stress on that the high coverage of adequate iodized salt which can save IQ played a critical role on the improvement of children cognition,the whole growing period of children in IDD areas.