| Objective: At both ends of the spectrum,inadequacy or excess of iodine intake can lead to thyroid disorders.As a country suffering from mild to moderate iodine deficiency,China implemented Universal Salt Iodization(USI)legislation nationally in 1996,covering all 31 provincial regions of mainland China.The success of USI was honored by that 28 provinces had reached the goal of eliminating iodine deficient disorders(IDD)and the other 3 were close to this goal,according to the data collected by 2010.During the two decades of USI enactment,the Chinese population has been consecutively exposed to an iodine nutrition status of excessive iodine intake(EI;median UIC ?300 ?g/L)for 5 years(1996-2001),more than adequate iodine intake(MAI;median UIC 200-299 ?g/L)for 10 years(2002-2011),and adequate iodine intake(AI;median UIC 100-199 ?g/L)for 5 years(2012-2016).Twenty years after the commencement of USI,the present cross-sectional study at the national scale across China,conducted between 2015-2017,aims to re-evaluate the current situation of iodine nutrition and the prevalence of thyroid disorders,as well as the relationships between them.Thyroid hormone level is important in both growth and metabolism of human body.Several studies have shown that thyroid hormone levels are associated with blood glucose,blood pressure and blood lipids in adults.However,previous studies are mainly based on participants with abnormal thyroid function or dyslipidemia.Whether the increase of thyroid stimulating hormone(TSH)levels within the normal range could incrase the risk of metabolism syndrome(Met S)is still controversial.In addition,these epidemiological studies are limited to small sample size and subpopulations,and the relationship between TSH levels and Met S and related components has not been systematically reported.Therefore,the second part of this study aimed to investigate the epidemiological relationship between different TSH levels within the normal range and Met S and its components.In addition,with rapid economic development in the past three decades,the Chinese population has been experienced rapid lifestyle change.This change has resulted in the increased prevalence of overweight.The prevalence of diabetes in adults living in China increased from 0.67% using the World Health Organization(WHO)criteria in 1980 to 10.9% using the American Diabetes Association(ADA)criteria in 2013.Although different sampling methods and screening procedures were used from 1980 to 2013,these data documents a dramatic increase.According to International Diabetes Federat ion Diabetes Atlas,China has the largest number of the patients with diabetes in the world,and it is estimated that there are 113.9 million adults with diabetes living in China which accounts for 24% of global diabetes patients.China implemented health care reforms,from 2013.As a result,patients with noncommunicable diseases including diabetes,may have easier access to clinical resources and thereby improve their diabetes control.Some areas have carried out a whole population diabetes and other NCDs prevention,screening,diagnosis and management project.The priority of prevention and treatment of diabetes has shifted from large general hospitals to community health service centers,from simple clinical treatment to tertiary prevention of diabetes,and from simple control of blood glucose to control of weight,blood glucose,blood pressure and blood lipids.Our objective of the third part of this study was to perform this cross-sectional study on the prevalence of diabetes and prediabetes in mainland China,and to evaluate awareness,treatment and control of diabetes by geographical location and subpopulation.Commissioned by the original National Health and Family Planning Commission and the Chinese Medical Association,our research team led the implementation of Thyroid Disorders,Iodine Status and Diabetes: a National Epidemiological Survey(TIDE project)in 31 provinces,municipalities and autonomous regions across the country from 2015 to 2017.The data for this study comes from the TIDE project.Methods: We used a multistage,stratified sampling method to select a nationally representative sample of persons 18 years of age and older in the general population.The study was conducted through four stages of random sampling in urban and rural locations in parallel.For urban locations,at the first stage,one prefecture-level city was selected from each province in all 31 provinces of China.These 31 prefecture-level cities were classified as 10 developed,13 developing and 8 underdeveloped cities.At the second stage,one district was randomly selected from each city.At the third stage,two residential communities were randomly selected from the district.At the final stage,eligible individuals who met the inclusion criteria and were from the list of the local resident registration were randomly selected and stratified by age and sex.The age and sex composition of each community and urban-rural ratio were decided based on China's 2010 national census data.Parallel random sampling was performed in rural locations.The inclusion criteria of the adult respondents were: aged 18 years or older;living in the selected community for at least 5 years;non-pregnant women.If one minority was chosen from the autonomous region for ethnic minorities,then at least 1000 minority participants were recruited in this region.The content of the standard questionnaire included demographic characteristics,personal and family medical history of thyroid disorders,personal and family medical history of diabetes,current smoking status,family income,education levels and household salt consumption.From each participant,fasting blood and spot urine samples were collected.For participants who were not diagnosed with diabetes previously,2-hour plasma glucose(2hPG)levels after an oral 75 g glucose tolerance test(OGTT)was performed.All participants underwent thyroid ultrasonography by qualified observers using a portable instrument.Urinary iodine concentration(UIC)was determined using inductively coupled plasma mass spectrometry.Serum thyroid stimulating hormone(TSH),thyroid peroxidase antibodies(TPOAb)and thyroglobulin antibodies(TgAb)were measured,using an electrochemiluminescence immunoassay.Free thyroxine(FT4)and free triiodothyronine(FT3)levels were measured only if TSH was outside the reference range.TSH receptor antibodies(TRAb)were tested in subjects with TSH below 0.27mIU/L.HbA1 c was measured from venous blood samples using a high-performance liquid chromatography method.FPG,2hPG,serum total cholesterol,low-density lipoprotein cholesterol(LDL-C),high-density lipoprotein cholesterol(HDL-C),and triglycerides(Tg)were measured using an automatic biochemical analyzer.To account for the complex sampling design of this study,we used SUDAAN software to obtain estimates of prevalence and the standard errors on the basis of the Taylor series linearization method.Estimates were weighted to reflect age,sex,and urban/rural,province distribution of the adults living in China.Weighting coefficients were derived from the 2010 Chinese population census data and the sampling scheme of the current survey was to obtain a national estimate.Results: 80937 participants had completed the study.Among them,participants with missing information on sex,age or thyroid function tests,metabolism or diabetes related tests were excluded.Thus,78470 samples remained eligible for iodine and thyroid disorders analysis,60257 samples for TSH levels and Met S analysis and 75880 samples for diabetes analysis.The median UIC in school-age children was 199.75?g/L with a goiter prevalence of 3.50%.The median UIC in the adult population was 177.89?g/L and the prevalence of goiter was 1.17%.The weighted prevalence of thyroid disorders in adults were as follows: 0.78% of overt hyperthyroidism,0.44% of subclinical hyperthyroidism,0.53% of Graves' disease,1.02% of overt hypothyroidism,12.93% of subclinical hypothyroidism,14.19% of positive thyroid antibodies(Ab),10.19% of positive TPOAb,9.70% of positive TgAb,and 20.43% of thyroid nodules.Iodine excess was only associated with higher odds of overt hyperthyroidism and subclinical hypothyroidism,while iodine deficiency was significantly associated with higher odds of most thyroid disorders.In addition,increased iodine intake was significantly associated with elevated serum TSH levels,but was inversely associated with thyroid antibodies and thyroid nodule.Compared with the non-Met S group,TSH level in patients with low HDL was significantly increased(2.29mIU/L vs.2.21mIU/L,p<0.001),and TSH level was significantly decreased in patients with hyperglycemia(2.16mIU/L vs.2.21mIU/L,p<0.001).With the increase of TSH levels,the risk of Mets and the number of components increased significantly.After adjusting for other confounding factors,high TSH level within the normal range was associated with higher risk of high blood pressure(OR=1.10,95%CI,1.01-1.15,p<0.001),hypertriglyceridemia(OR=1.05,95%CI,1.00-1.11,p=0.039)and low HDL(OR=1.08,95%CI,1.03-1.14,p=0.002).The weighted prevalence of total diabetes,self-reported diabetes,newly diagnosed diabetes and prediabetes diagnosed by the ADA criteria were 12.8%,6.0%,6.8% and 35.2%,respectively,among adults living in China.The weighted prevalence of total diabetes was higher among 50 years and older and among men.The prevalence of total diabetes in 31 provinces ranged from 6.2% in Guizhou to 19.9% in Inner Mongolia.Han ethnicity had the highest prevalence of diabetes(12.8%),followed by Uygur ethnicity(11.5%),Zhuang ethnicity(11.4%),Tibetan ethnicity(6.5%)and Hui ethnicity(6.3%).The awareness,treatment and control rate of diabetes were 43.3%,49.0% and 49.4%,respectively.The weighted prevalence of total diabetes using the WHO criteria in this study was 11.2%.Conclusion: The long-term mandatory USI program with timely adjustments is successful in preventing iodine deficiency disorders and it appears to be safe.The benefits outweigh the risks in a population with a stable median iodine intake level of up to 300?g/L.Elevated TSH within the normal range is a metabolic risk marker associated with Met S,elevated blood pressure,hypertriglyceridemia and low HDL.The prevalence of diabetes has slightly increased from 2007 to 2017 among adults living in China.Our findings indicate that diabetes is an important health problem in China.Ongoing consecutive surveillance and effective control are needed to reduce the burden of diabetes. |
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