Saliva iodine concentration is positively correlated with urinary iodine concentration and can serve as a good biomarker of recent iodine status in school-aged children, according to study results published in the Journal of Clinical Endocrinology & Metabolism.
While urinary iodine concentration is the most common method of assessing iodine status, it has several limitations, including the need for repeated urine samples and difficulties in collecting a 24-hour sample. Previous studies reported an association between saliva iodine concentration and iodine status, but the data are limited.
The goal of the current study was to investigate the association between saliva iodine concentration and iodine intake, urinary iodine concentration, and thyroid function.
The cross-sectional study included children aged 8 to 13 years in Shandong, China, during May 2019. The researchers excluded patients with a previous history of thyroid disease or use of iodine medication. All participants completed a 24-hour urine collection and both provided spot urine and saliva samples.
The study cohort included 423 children (223 boys, mean age 10.3±1.0 years). The median value of spot urinary iodine concentration was 124 µg/L, indicating adequate iodine status. The median saliva iodine concentration was 106 µg/L in boys (interquartile range [IQR]: 67.9-185 µg/L) and 106 µg/L in girls (IQR: 66.3-175 µg/L).
Statistical analysis showed a positive correlation between saliva iodine concentration and spot urinary iodine concentration (r = .27, P < .0001), 24-hour urinary iodine concentration (r = .37, P < .0001), and 24-hour urinary iodine excretion (r = .40, P < .0001). These data suggest that saliva iodine concentration is also valuable in evaluating the recent iodine status.
The optimal cut-off points of saliva iodine concentration for assessing iodine deficiency or iodine excess were <105 µg/L and >273 µg/L, respectively. The prevalence of insufficient estimated iodine intake and 24-hour urinary iodine concentration <100 µg/L were increased in children with saliva iodine concentration <105 µg/L (odds ratio [OR], 2.74; 95% CI, 1.77-4.24 and OR, 4.18; 95% CI, 2.67-6.56; respectively) than those with higher saliva iodine concentration values.
Similarly, the prevalence of excess iodine intake and 24-hour urinary iodine concentration >300 µg/L were increased in children with saliva iodine concentration >273 µg/L (OR, 9.42; 95% CI, 4.12-21.54 and OR, 18.56; 95% CI, 5.66-60.91; respectively). In addition, the risk for thyroid nodules was greater in children with saliva iodine concentration >273 µg/L (OR, 2.70; 95% CI, 1.38-5.26), compared with those with lower saliva iodine concentration values.
There were no significant correlations between saliva iodine concentration with serum iodine and thyroid function indicators.
The study had several limitations, including the small sample size and the inclusion of only a few children with excessive iodine status.
“Given the sanitary nature and convenience of saliva iodine collection, [saliva iodine concentration] is highly recommended as a good biomarker of school-aged children’s recent iodine status,” the researchers concluded.
Guo W, Pan Z, Zhang Y, et al. Saliva iodine concentration in children and its association with iodine status and thyroid function. Published online July 20, 2020. J Clin Endocrinol Metab. doi: 2020;105(9):dgaa471.