In order to solve the bottleneck problems of"zero balance displacement"and"large variation of breastmilk"in the study of iodine EAR of pregnant women, lactating women and infants, firstly, this study intends to clarify the rate of metabolism and distribution of iodine during pregnancy by 125I tracer, SPECT/CT in vivo small animal imaging and γ counting study. Then, the iodine balance study in rats was conducted to verify the degree of "zero balance value displacement"caused by the difference of iodine absorption and store in different organs and tissues under different iodine exposure levels, so as to determine the iodine selection conditions of subjects in the population experiment. To determine the EAR of pregnant women by optimizing the population iodine balance experiment. Secondly, we proposed to study the regulatory mechanism of NIS and Pendrin in the mammary gland of lactating rats under different iodine nutrition levels to clarify the range of breastmilk iodine compensation. Mammary cell experiments intend to clarify the mutual regulations of iodine nutrition, oestrogen, and NIS and Pendrin. Based on the results of animal and cellular experiments, and the effect of genetic, oestrogen and iodine status were considered, a cross-sectional study of lactating women was conducted to determine the normal reference range of breastmilk iodine after screening out the people with abnormal indicators. This study will solve the bottleneck problems and difficulties in the iodine RNI research for pregnant women, lactating women and infants, found the iodine nutritional compensatory mechanism under special physiology, and provide the scientific basis for obtaining the accurate EAR basic data and the revision of iodine DRIs.

In this study, the absorption, distribution, storage and excretion of 125I in rats were observed by small animal imaging technology in vivo, so as to clarify the characteristics of iodine metabolism under different iodine exposure, and provide a basis for optimizing the experimental cycle of iodine balance experiment. The iodine balance experiment of rats during pregnancy was carried out, the iodine storage in different organs was detected to explain the phenomenon of "zero point balance value shift", and the population with iodine nutrition background was determined as the experimental objects in the iodine balance experiment. The optimized iodine balance experiment was further verified in the population, and the iodine EAR of pregnant women was explored to provide reference data for formulating the recommended iodine intake of pregnant women in China in the future. The expression difference of NIS and Pendrin in lactating rats with different iodine nutritional status was used to determine the range of milk iodine compensation. To determine the synergistic and independent effects of iodine level and estrogen on the expression of NIS and Pendrin in lactating mammary gland cells cultured in primary culture. Through a cross-section study of lactating women, the correlation between milk iodine level and NIS, Pendrin gene mutation, iodine exposure level and estrogen was discussed, the phenomenon of "huge milk iodine variation" was explained, the normal reference range of milk iodine was defined, and the basis was laid for further determination of iodine AI and EAR of lactating mothers in 0-6 months. To clarify the steady-state mechanism of iodine metabolism in pregnancy-milk during special physiological periods with different iodine exposure levels, research ideas and related research results can also provide references for the determination of other nutrient requirements.

Inclusion Criteria:

Pregnant women:

• Aged 18-40, who have lived in the area for ≥5 year;
• Single pregnancy;
• Those who have no special dietary habits;

Lactating woman:

• Breastfeeding a child;
• Normal thyroid function during pregnancy;
• Term delivery (38-42 weeks of gestation);

Exclusion Criteria:

Pregnant women:

• Smoking or drinking;
• Iodized drugs or contrast agents have been used in the past year;
• A history of thyroid disease, autoimmune disease, endocrine disease, heart disease, chronic disease or family hereditary disease, etc

Lactating woman:

• A history of thyroid disease, autoimmune disease, endocrine disease, heart disease, chronic disease or family hereditary disease, etc;
• Iodized drugs or contrast agents have been used;

Women in the third trimester (18-40 years old), lactating women (38-42 weeks of gestation), all from Tianjin, Xinjiang and Gansu.