Prevalence of thyroid dysfunction in healthy adults according to the estimated iodine intake in 24-hour urine samples: The SALMEX cohort.

PURPOSE: The aim of this study was to evaluate the prevalence of thyroid dysfunction in a cohort of healthy individuals in Mexico City, as well as to investigate the potential associations of these results with their estimated iodine intake (EII) as reflected by their 24-hour urinary iodine excretion (24-h UIE).

METHODS

From the SALMEX cohort, 683 adults provided an appropriate 24-h urine sample. Thyroid function tests and thyroid antibody concentrations were determined in the participants' sera. We analyzed discrepancies between the commonly used urinary parameters to determine the iodine intake status and the performance of thyroglobulin (Tg) as a biomarker of its status in the adult population.

RESULTS

The prevalence of dysthyroidism was high, being similar to other studies. Subclinical hypothyroidism was detected in 5.0% of individuals, clinical hypothyroidism in 1.8% of individuals, and sub-clinical hyperthyroidism in 2.8% of individuals. The median EII was 285 μg/d (IQR 215.0-369.0); 94% of individuals had EII >150 µg/d recommended daily allowance (RDA) in adults. The urinary iodine concentration (UIC) and the UIE had relative biases in their averages of 34.4%. The Tg median was 7.21 ng/mL. The prevalence of increased Tg was 6.15%. There was no correlation between Tg and EII (r= 0.019, p= 0.606).

CONCLUSIONS

Thyroid dysfunction was highly prevalent in this population. Our cohort revealed a slight discrepancy between dysthyroidism manifestations and iodine intake markers; the latter represent a population with adequate iodine intake. Further studies are necessary to clearly define the prevalence of thyroid dysfunction as well as the iodine nutritional status in Mexico.