Study On The Effects Of Different Iodine Intake On People's Thyroid And Lipid And The Iodine Safe Intake Level

Objective 1. To understand the subjects'iodine nutrition status and resource.2. To explore the Chinese iodine Lowest Observed Adverse Effect Level (LOAEL) in the range of 0～400μg/d based on the protophase work so as to provide data to amend Chinese iodine tolerable Upper Intake Level (UL), prevent the iodine excess and adjust the iodine concertration in salt.3. To research the hazard of iodine excess to healthy Chinese thyroid and lipid in the range of 0～400μg I/d.Methods 1. Recruit and screen the Volunteers:recruit 114 volunteers (men 58, women 56) in Tianjin Medical University through the way of register, and then detect their height, weight, thyroid hormone (FT3, FT4), sTSH, TGAb and TMAb. Reject the individual with abnormal FT3, FT4, sTSH TGAb or TMAb and get 95 healthy volunteers (men 55, women 40).2. Group and iodine intervention:95 volunteers were divided into 5 groups according to gender and age, and then they were given 0μg/d (control group), 100μg/d,200μg/d,300μg/d,400μg/d iodine supplement separately for 4 weeks.3. Collect and detect the indexes:collect urina sanguinis, fasting blood and detect thyroid volume at 0 week, the end of 2 week and 4 week respectivly. Collect the sample of water, salt and food. Detect serum FT3, FT4 and sTSH with Chemiluminescence; TGAb and TMAb with Radioimmunoassay; HDL, CHO and TG with Biochemistry. Detect urine and water iodine concertration with Arsenic-cerium contact chromatometry; salt iodine concertration with Direct titration; salt in food with Electric potential titration. Follow-up parts of volunteers and sampled their fasting blood to detect FT3, FT4, sTSH after 3 months and 9 months of completing the intervention. Detect volunteers'thyroid volume in 200～400μg/d groups after 9 months.4. Dietary survey:survey all of volunteers with a 7-day 24-hour dietary recording method. The iodine contents of food sold in Tianjin got from previous database.Result 1. The intake of nutrients, energy and protein reached 80% RNIs except vitamin B1, vitamin B2, calcium and vitamin A (only women). The intake of fat was excessive. The iodine intake from the food (including salt) was 346.60±25.32μg/d, and 68.18% iodine came from iodization salt.2. The Median Urinary Iodine (MUI) was 300.30～381.30μg/L before supplying iodine. It significantly increased to 438.50～671.50μg/L in iodine supplement groups 4 weeks later (P<0.05).3. Compared with 0 week, FT4,sTSH increased significantly at the end of 4 week (P<0.05) in each group, but their level was not beyond the references. It appeared one subclinical hypothyroidism adividual respectively in group with 300μg I/d and 400μg I/d. The incidence was 5.26%. The volunteers were followed-up after 3 months of completing the intervention and the adividual in group with 300μg I/d self-cured. After 9 months, the adividual's sTSH in group with 300μg I/d decreased to cut off.4. Compared with 0 week, TGAb and TMAb in serum had no significant change at the end of 4 week (P>0.05).5. The volunteers' thyroid volume had an increasing tendency in all iodine supplement groups and the groups with 200μg I/d and 300μg I/d increased significantly at the end of 4 week (P<0.05), but the average in each group was still in the range of normal. There was no goiter. After 9 month, parts of volunteers' thyroid volume had no significant change compared with 0 week in groups with 200～400μg I/d (P>0.05).6. Compared with 0 week, HDL, CHO and LDL decreased significantly in group with 100μg I/d,200μg I/d and 300μg I/d at the end of 4 week (P<0.05), but their averages were still normal. There was no lipid disorder adividual.Conclusion 1. Tianjin was iodine deficiency area. The residents had to intake iodized salt to ensure the need. But the iodine content in the salt was a little high for the residents in Tianjin and their iodine status was excess.2. There was no impact to most health people (95%) living in non-iodine deficiency area on thyroid function if the iodine intake was 771.62μg/d (400μg/d iodine supplement+371.62μg/d dietary iodine) and less than that dose. The risk of eliciting AITD, thyroid paramorphia and lipid disorder was low. To parts of people, it was easy to cause subclinical hypothyroidism. So it suggested that the iodine UL is lower than 800μg/d to Chinese. 3. It was important to subclinical hypothyroidism patients to stop intaking excessive iodine in order to prevent and control the disease. We suggested subclinical hypothyroidism patients should stop contacting more iodine.