Salivary iodine concentrations can estimate iodine intake and diagnose abnormal thyroid function: a cross-sectional study in pregnant and lactating women in iodine-deficient areas

Salivary iodine concentrations (SIC) and urinary iodine concentrations are correlated. This study aimed to verify the use of SIC as a biomarker for estimating iodine intake in pregnant and lactating women and to diagnose abnormal thyroid function. A cross-sectional study was conducted in northern Xinjiang, China. Participants provided venous blood, random urine, saliva and milk samples. A total of 607 pregnant and 171 lactating women volunteered to participate in the study. The average daily iodine intake was calculated for each participant. Pregnant women were divided according to trimester. The median daily iodine intake was 436·41 μg/d in the first trimester, 425·83 μg/d in the second trimester and 430·56 μg/d in the third trimester. The average daily iodine intake in lactating women was 416·16 μg/d. Different indicators were used to diagnose excessive iodine intake (> 500 μg/d). Among pregnant women, SIC had an AUC of 0·62 (<i>P</i> < 0·01), sensitivity of 51·75 % and specificity of 65 %. Among lactating women, SIC had an AUC of 0·63 (<i>P</i> = 0·03), sensitivity of 43·52 % and specificity of 85 %. SIC was an effective biomarker for diagnosing abnormal thyroid function (<i>P</i> = 0·03). In conclusion, this study demonstrated that SIC is a reliable biomarker for evaluating both iodine nutrition status and abnormal thyroid function in pregnant and lactating women.