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Estimation of total body iodine content in normal young men
1Nuclear Medicine Service, VA Palo Alto Health Care System and Department of Radiology, Stanford University School of Medicine, California 94306, USA. mhays19@home.com
Insights
This study estimated total body iodine in men using iodine-125 (125I) balance studies. Results indicate an average total body iodine content of 14.6 mg, crucial for understanding iodine metabolism.
Area of Science:
- Biochemistry
- Human Physiology
- Nuclear Medicine
Background:
- Accurate estimation of total body iodine is essential for understanding iodine kinetics and nutritional status.
- Previous methods for determining body iodine content have limitations in precision and scope.
Purpose of the Study:
- To estimate total body iodine content in normal young men.
- To determine the extrathyroidal to total iodine ratio using iodine-125 (125I) balance studies.
Main Methods:
- Six healthy men underwent daily 125I administration for 64-92 days.
- Total body retention of 125I was calculated by subtracting urinary and fecal excretion from administered amounts.
- Extrathyroidal 125I was determined as the difference between total and thyroidal 125I.
Main Results:
- The asymptotic extrathyroidal/total 125I ratio was estimated to be 0.34 (range, 0.19-0.63).
- The time to achieve 125I/127I equilibration was predicted to be approximately 10 months.
- Assuming 90% measurement accuracy of iodine loss and 10 mg thyroid iodine, the mean total body iodine was 14.6 mg (range, 12.1-25.3 mg).
Conclusions:
- The study provides an estimate for total body iodine content in normal adult males.
- Findings contribute to a better understanding of iodine distribution and kinetics within the human body.
- The methodology offers a basis for further research into iodine balance and requirements.
Abstract:
Total body iodine content was estimated in six normal young men, who underwent 125I balance studies during 64-92 days of daily 125I administration. Total body retention of 125I was measured as the difference between total administered 125I and that collected in the urine and feces. Extrathyroidal 125I was the difference between total and thyroidal 125I content. The time-activity data for the ratio of extrathyroidal to total retained 125I were fitted to a growth (inverse exponential) function. Fits of this growth function to the individual data sets yielded asymptotes, the equilibrium extrathyroidal/total 125I ratios. The slopes of this function predicted the time that would have been required to achieve 125I/127I equilibration (approximately 10 months). Geometric mean for the asymptotic extrathyroidal/total 125I ratio was 0.34 (range, 0.19-0.63), if it was assumed that measured urine and feces represented all of the 125I lost to the body. If 90% measurement of 125I loss was assumed, the geometric mean ratio was 0.32 (range, 0.17-0.60). Assuming that 90% of total loss is reflected in measured excreta and that total iodine content of the thyroid gland is 10 mg, geometric mean for total body iodine in these subjects was 14.6 mg (range, 12.1-25.3 mg).
