J Nutr Health.  2022 Apr;55(2):250-262. 10.4163/jnh.2022.55.2.250.

Effect of iodine restriction on short-term changes in thyroid function in patients with subclinical hypothyroidism

• Kwon O
• Shin DY
• Lee EJ

• KMID: 2529469
• DOI: http://doi.org/10.4163/jnh.2022.55.2.250

Abstract

Purpose
Elevated iodine intake is related to a higher prevalence of subclinical hypothyroidism (SCH). We investigated the short-term effect of dietary iodine restriction on thyroid function in patients with SCH with high iodine intakes.
Methods
The iodine levels in 64 SCH patients with serum TSH levels from 4.0 to 10.0 mIU/L and normal serum fT4 levels (n = 64) were assessed using 24-hour urine iodine test results and iodine intake levels calculated using a semi-quantitative food frequency questionnaire. Dietary iodine restriction was not recommended for patients with an iodine intake in the normal range (group A, n = 13), but seaweed restriction was recommended for patients with high iodine intakes (group B, n = 33). Thyroid functions and iodine levels were rechecked after three months. Another eighteen patients were prescribed thyroid hormone replacement therapy according to clinical criteria.
Results
Median baseline iodine intake for the 64 patients was 290.61 μg/day, and median 24-hour urine iodine was 33.65 μmol/g of creatinine. The major source of dietary iodine was seaweed, which accounted for 72.2% of median baseline intake. Urine iodine and calculated iodine intake levels were positively correlated with serum TSH levels (p < 0.001 and p = 0.027, respectively), and calculated iodine intakes were significantly correlated with urine iodine levels (p = 0.001). In group B, iodine restriction significantly decreased urine iodine (p = 0.042) and TSH levels (p = 0.004), and conversion to euthyroid status was achieved in 16 of the 33 patients (48.5%).
Conclusion
Iodine intake and urine iodine levels are correlated with thyroid function in SCH patients, and dietary iodine restriction can aid functional thyroid recovery in patients with elevated iodine intakes.

Keyword

subclinical hypothyroidism; iodine; thyroid gland