Longitudinal trends in thyroid function in relation to iodine intake: ongoing changes of thyroid function despite...

Area of Science:

• Endocrinology
• Thyroid Research
• Nutritional Science

Background:

• Iodine deficiency historically impacts thyroid function.
• Cross-sectional studies show varied TSH-age associations based on iodine status.
• The long-term effects of past iodine insufficiency on thyroid function require longitudinal investigation.

Purpose of the Study:

• To investigate the longitudinal relationship between age and thyroid function in a population with a history of borderline iodine status.
• To determine if observed age-related thyroid function changes reflect current or past iodine status.

Main Methods:

• Longitudinal study of 980 participants from the Nijmegen Biomedical Study.
• Measurement of serum TSH, FT₄, T₃, thyroid peroxidase antibodies, and urinary iodine/creatinine.
• Follow-up assessment 4 years after initial thyroid function survey.

Main Results:

• TSH levels decreased by 5.4% and FT₄ increased by 3.7% over 4 years.
• Median urinary iodine concentration was 130 μg/L, indicating adequate iodine status.
• Lower iodine intake was weakly associated with higher FT₄ levels.

Conclusions:

• A longitudinal decrease in TSH and increase in FT₄ was observed in a previously iodine-insufficient population.
• These findings suggest that early-life iodine insufficiency may lead to persistent thyroid autonomy.
• Thyroid autonomy may manifest as a tendency towards hyperthyroidism, persisting despite adequate iodine intake in adulthood.