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Variations in urinary iodine excretion and thyroid function. A 1-year study in healthy men
S Andersen1, K M Pedersen, I B Pedersen
1Department of Endocrinology and Medicine, Aalborg Hospital, Reberbansgade, DK-9000 Aalborg, Denmark. stiga@dadlnet.dk
European Journal of Endocrinology
|May 2, 2001
Summary
Urinary iodine levels can fluctuate daily, potentially misrepresenting iodine deficiency. Using 24-hour urinary iodine excretion estimates reduces variability and provides a more accurate population assessment.
Area of Science:
- Endocrinology
- Nutritional Science
- Public Health
Background:
- Assessing population iodine intake relies on cross-sectional studies.
- Urinary iodine concentration (UIC) is a common biomarker.
- Daily variations in urinary iodine can lead to misinterpretation of iodine deficiency.
Purpose of the Study:
- To evaluate the impact of daily fluctuations on iodine status assessment.
- To compare the accuracy of single spot urine samples versus 24-hour collections.
- To investigate the relationship between iodine intake and thyroid function markers.
Main Methods:
- A longitudinal study involving 16 healthy men in an iodine-deficient area.
- Monthly measurements of urinary iodine and creatinine.
- Analysis of serum thyroid-stimulating hormone (TSH), thyroxine (T4), and tri-iodothyronine (T3) over one year.
Main Results:
- Average urinary iodine excretion was 57.0 µg/l (49.1 µg/24h).
- Individual samples showed significant variation (10-260 µg/l), with 6.7% below 25 µg/l.
- Estimated 24-hour urinary iodine excretion reduced variability by 24% compared to UIC.
- Correlation between iodine excretion and TSH differed based on deficiency severity.
Conclusions:
- A small fraction of individual samples may falsely indicate severe iodine deficiency.
- Estimated 24-hour urinary iodine excretion is a more reliable measure than spot UIC.
- Moderate iodine deficiency (25-50 µg/24h) impacts thyroid hormone synthesis, unlike mild deficiency (50-100 µg/24h).